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INTRODUCTION 


TO 


CHEMICAL   PHYSICS, 


DESIGNED  FOR  THE  USE  OF 


ACADEMIES,  HIGH  SCHOOLS,  AND  COLLEGES. 


ILLUSTRATED   WITII   NUMEROUS   ENGRAVINGS, 
AND   CONTAINING  COPIOUS  LISTS  OF  EXPERIMENTS  WITH  DIRECTIONS  FOR  PREPARING  THEM. 


BY 

THOMAS  RUGGLES  PYNCHON,  M.  A., 

SCOVIIX   PROFESSOR   OF    CHEMISTRY    AND    THE    NATURAL   SCIENCES, 
TRIMTY    COLLEGE,    HARTFORD. 

M  B  i»  A  :l 

NEW  EDITION,  REVISED  A&D  iSKlkAo^  I  4  S  I 

*          >  I  *      *      | 


CALIFORNIA. 

—  •     .- 


NEW    YORK: 

D.  VAN  NOSTRAND,  23  MURRAY  &  27  WARREN  STREET. 

1873. 


Entered  according  to  Act  of  Congress,  in  the  year  1872,  by 

THOMAS  RUGGLES  PYNCHON, 
In  the  Office  of  the  Librarian  of  Congress,  at  Washington. 


T  O  T  II  E     MEMORY 
OF 

Dtt.    JOSEPH    BLACK, 

DUUING     A    LONG     LIFE,     PliOFESSOU     OF    CllB.MZi.TKr 

IN     THE     UNIVERSITIES     OF    GLASGOW     AND     OF     EDINBURGH, 

THE   FRIEND   AND    ADVISER   OF 

JAMES    W A  T  T  , 

AND  THE  DISCOVERER  OF  THOSE  LAWS  OF  LATKXT  HKAT 

WHICH   LEO   TO    THE    WONDERFUL   IMPROVEMENTS   IN    TIIR    STKAK    EXO 

THIS  VOLUME,  DEVOTED  CHIEPLV  TO  THE  EUJCIDATtOW 

OF  THE  SAME  AND  KINDRED  SUBJECTS, 

IS   RESPECTFULLY  INSCRIBED 

BY 

AN  ARDENT  ADMIRER  OF 
HIS  GENIUS 


PREFACE. 


THIS  Treatise  has  been  prepared  for  the  use  of  the  general 
reader,  as  well  as  for  that  of  Students  in  Academies,  Colleges, 
and  Medical  Schools,  and  is  designed  to  embody  the  most  im- 
portant facts  and  principles  of  the  Physical  Forces, —  Heat, 
Light,  and  Electricity,  that  have  any  connection  with  the  pro- 
duction of  Chemical  phenomena,  and  to  form  an  introduction  to 
the  study  of  the  science  of  Chemistry.  With  that  science 
these  subjects  are  so  closely  associated  that  they  may  be  sail 
to  constitute  a  part  of  it,  and  a  thorough  knowledge  of  them  is 
absolutely  indispensable  to  its  satisfactory  study.  They  are 
also  possessed  of  great  intrinsic  interest,  and  are  intimately 
connected  with  all  the  mo  t  important  scientific  inventions  of 
the  Age, — the  Steam  Engine,  Photography,  the  Electric  Tele- 
graph, and  others,  as  well  as  with  many  of  the  great  processes 
of  Nature,  in  constant  operation  around  us,  and  these  cannot 
be  understood  without  a  thorough  knowledge  of  their  element- 
a  y  Principles. 

At  the  same  time  they  are  among  the  most  difficult  portions 
of  Physical  Science,  and  for  their  thorough  understanding 
a  considerable  amount  of  minute  explanation  and  illustration 
is  required.  The  author  has,  therefore,  treated  them  with  some 
copiousness  of  detail,  and  has  endeavored  to  avoid  that  meagre- 
ness  of  statement  which  aims  to  present  only  the  bare  facts  of 


VI  PREFACE. 

science ;  while  at  the  same  time  he  has  sought  not  to  exceed 
the  limit  beyond  which  his  readers  would  be  unable  to  follow 
him  without  the  aid  of  Mathematics.  All  matters  of  which  a 
knowledge  could  equally  well  be  obtained  from  any  good  treat- 
ise on  Natural  Philosophy  have  been  omitted;  and  those 
points  have  been  elucidated  with  special  care,  which  a  some- 
what extended  experience  as  an  Instructor  has  shown  to  be 
peculiarly  difficult  of  comprehension  by  the  student. 

The  subjects  which  have  been  most  carefully  elaborated,  are 
Heat ;  R'idiant  Heat ;  the  transmission  of  Heat  through  me- 
dia ;  Latent  Heat ;  the  Steam  Engine  ;  the  Chemical  Influence 
of  Light;  Photography;  Spectrum  Analysis;  the  Galvanic 
Battery,  and  its  heating,  illuminating,  chemical  and  magnetic 
effects ;  the  Electric  Telegraph  ;  the  Atlantic  Telegraph ;  Elec- 
tro-Magnetic Engines  ;  the  Fire-Alarm  of  Cities  ;  the  Induction 
Coils  of  Page  and  Rahmkorff;  the  Mag  ^to-Electric  Machines 
of  Saxton,  Page,  Holmes,  Wilde,  and  Ladd,  and  their  various 
applications  to  Electro-Plating  and  Gilding,  to  the  illumination 
of  Light- Houses,  and  to  Medicine.  Much  attention  has  been 
paid  to  the  modern  Theory  of  the  Correlation,  Convertibility  and 
Equivalency  of  the  Physical  Forces.  Great  pains  has  also  been 
taken  to  trace  the  history  of  the  various  scientific  discoveries 
described,  and  to  give  to  their  Authors  the  merit  which  is 
justly  their  due.  And  at  the  end  of  every  Section  copious 
Lists  of  Experiments  have  been  introduced,  with  minute  direc- 
tions for  their  preparation  and  performance,  arranged  with 
reference  to  the  convenience  of  teachers  as  well  as  of  students. 
It  is  believed  that  these  Lists  are  much  more  complete  than 
any  heretofore  published. 

An  attempt  has  been  made,  both  in  the  arrangement  of  para- 


PREFACE.  Vii 

r 

grnphs,  and  in  their  printing,  to  place  the  subject  before  the 
student  in  a  distinct  light,  and  in  a  clear  and  systematic  man- 
ner. Besides  a  full  catalogue  of  subjects  at  the  beginning,  for 
general  use,  a  running  title  has  been  put  at  the  top  of  each 
page,  and  every  paragraph  provided  with  a  heading  printed  in 
heavy  type,  for  the  purpose  of  furnishing  a  continuous  Table 
of  Contents,  subject  by  subject,  and  also  of  enabling  the  teachei 
to  select  those  portions  which  he  may  deem  the  best  adapted  to 
the  wants  of  the  student,  whenever,  for  any  reason,  it  is  thought 
expedient  not  to  attempt  the  study  of  the  whole. 

As  the  merit  of  an  elementary  treatise  like  the  present,  must 
consist  rather  in  the  judgment  shown  in  the  selection  and  ar- 
rangement of  materials  than  in  the  originality  of  its  contents, 
the  Author  has  not  scrupled  to  avail  himself  of  aid  from  every 
quarter.  The  works  most  frequently  consulted  have  been  Ga- 
not's  Traite  de  Physique,  Pouillet's  Elements  de  Physique,  and 
Miller's  Chemical  Physics.  The  illustrations,  where  not  origi- 
nal, have  been  drawn  from  sources  equally  varied. 

Should  this  volume  meet  with  public  favor,  it  will  be  followed 
by  a  second  on  the  same  plan,  upon  Inorganic  and  Organic  Chem- 
is'ry.  The  Author  takes  this  opportunity  of  expressing  his  ac- 
knowledgements, for  many  important  suggestions,  to  several 
valued  friend 3,  and  particularly  to  Mr.  S.  H.  Clark,  of  Hart- 
ford, for  the  great  pains  which  he  has  bestowed  upon  the  en- 
gravings, and  for  the  fidelity  and  skill  with  which  he  has  exe- 
cuted them. 

T.  B..P. 
HAUTFOBD,  September  1st,  1869. 


TABLE  OF 


CHAPTER  I. 

INTRODUCTION. 

SUBJECT    MATTER    OF    CHEMISTRY;    ITSES ;    HISTORY.      THE    CHEMICAL 

AGENTS. 

PARAGRAPH.  PAGE. 

1.  ORIGIN  of  name,    --           -           -           •           .  •! 

2.  Chemistry  investigates  the  composition  of  Matter,  1 

3.  What  is  Matter  ?    -  ...      2 

4.  Matter  inert,  but  affected  by  external  forces,  2 

5.  The  three  states  of  Matter,  Solid,  Liquid  and  Gaseous,     •  3 

6.  The  properties  of  Solids,                                                             .  4 

7.  The  properties  of  Liquids,  -            •            •            •            .  -4 

8.  The  properties  of  Gases,           .....  5 

9.  The  Atmosphere  a  type  of  Gases.     Its  properties,             -  5 

10.  The  properties  of  Matter  treated  of  by  Natural  Philosophy,  -  7 

11.  The  properties  of  Matter  treated  of  by  Chemistry,  •      7 

12.  The  study  of  Matter  also  forms  the  subject  of  Mineralogy,  Botany 

and  Zoology,       -                        -            -  8 

13.  The  difference  between  Natural  Philosophy  and  Chemistry  illus- 

trated,     --*.-.            .  .      8 

14.  Chemistry  is  a  science  of  Experiment,             ...  9 

15.  What  is  a  Chemical  Experiment  ?-            -            -            -  -9 

16.  Chemistry  is  connected  with  many  processes  in  the  Arts,       •  10 

17.  Chemistry  explains  the  nature  of  Medicines,         •            -  -10 

18.  Chemistry  explains  Respiration,                        -            -            -  H 

19.  Chemistry  connected  with  Agriculture,       -            -            •  -    11 

20.  Chemistry  explains  the  extraction  of  Metals,  12 

21.  Chemistry  connected  with  the  manufacture  of  Gas,           ,  -    12 

22.  Chemistry  explains  Combustion,                       -            •            .  12 

23.  Importance  of  Chemistry,  -                                                  .  .    13 

24.  Chemistry  exhibits  striking  proofs  of  Design,           •            •  13 


TABLE    OF    CONTENTS. 


25.  The  history  of  Chemistry,  -  .     13 

26.  Chemistry  depends  upon  the  Balance,               -            -  -           14 

27.  Apparatus  required  in  Chemistry,  -            -            -            -  -     15 

28.  The  Fundamental  Principles  of  this  Science,  -            -  -           15 

29.  Simple  and  Compound  substances  distinguished,  -            -  -     16 
50.  The  term  Element  deh'ned,        •            -            -            .  .            16 

31.  The  number  of  the  Elements,          <            -            .            .  -     17 

32.  The  constitution  of  some  of  the  most  important  Chemical  com- 

pounds stated,      -            -            -            -            -            .  -17 

33.  Chemical  Affinity  defined,         -            -            -            -  -           is 

34.  The  active  Agents  of  Chemistry,    -                                      -  -     19 

35.  The  Chemical  Agents,  —  Heat,  Light,  Electricity,  why  called  Im- 

ponderables, -  20 

36.  The  study  of  Chemistry  begins  with  the  Chemical  Agents,  -    21 

CHAPTER  II. 

THE   FIRST    CHEMICAL    AGENT,    HEAT. 

DIFFUSION    OF    HF.AT,  —  EXPANSION;    LIQUEFACTION;    EBULLITION; 

EVAPORATION;  SPECIFIC  HEAT;  SOURCES  OF 

HEAT;  NATURE  OF  HEAT. 

§  I.  Diffusion  of  Heat. 

37.  The  Nature  of  Heat,                       -  -    22 

38.  Heat  exists  in  two  states,          .....  22 

39.  Heat  present  in  all  bodies,  -  -    23 

40.  Heat  and  Cold  relative  terms,  -                         -  23 

41.  Heat,  the  repulsive  principle  of  Matter,     -  -    24 

42.  Heat  tends  to  an  Equilibrium,  -  24 

43.  Three  modes  in  which  Heat  seeks  an  Equilibrium,            •  -25 

44.  First  mode.  —  Conduction,         -  26 

45.  46.  Bodies  differ  in  conducting  power,                   »            -  .26 

47.  Density  favorable  to  Conduction,  27 

48.  49.  Relative  conducting  power  of  the  Metals,        -           -  -    27 

50.  Porous  bodies  bad  conductors,  28 

51.  Illustrations  of  Conduction,            -             -            -             -  -    30 

52.  53.  Applications  in  the  Arts,   -                         -  31 

54.  Animals  and  Plants  protected  by  non-conducting  coverings,  -    32 

55.  Liquids  poor  conductors,  33 

56.  The  Gases  poor  conductors,                                                   -  -    34 

57.  The  conducting  power  of  different  Gases  different,  •          36 


TABLE    OF    CONTENTS.  XI 

PAR.  PAGE. 

58.'  The  second  mode  of  diffusion, — Convection,          -  -    37 

59.  Convection  in  Liquids,                                         •  37 

60.  Convection  in  Gases,  -            -    S3 

61.  Illustrations  of  Convection,      -  33 

62.  What  makes  heated  Water  and  Air  ascend,  -    40 

63.  The  ascension  of  heated  Liquids  and  Gases  illustrated,  41 

64.  The  third  mode  of  diffusion, — Radiation,  -    42 

65.  Radiant  Heat  follows  the  same  laws  as  Radiant  Light,  43 

66.  Nature  of  surface  affects  the  rate  of  Radiation,      -  -            -    43 

67.  Other  circumstances  affecting  the  rate  of  Radiation,  -  45 

68.  Radiation  takes  place  from  points  beneath  the  surface,  -            -    46 

69.  Practical  applications,  -  46 

70.  The  radiation  of  the  Earth,  -    47 

71.  The  theory  of  Radiation,                                    -  48 

72.  The  reflection  of  Radiant  Heat,      -  -    48 

73.  The  Law  of  the  reflection  of  Heat,       -  48 

74.  Concave  Mirrors,     -  -    49 

75.  Experiments  with  two  Concave  Mirrors,          -  50 

76.  The  different  reflecting  powers  of  different  substances,  -                 52 

77.  The  apparent  radiation  and  reflection  of  Cold,  53 

78.  The  material  of  Mirrors  affects  their  reflection,     -  -     53 

79.  Practical  applications,  -  54 

80.  The  reflection  of  Heat  by  Fire-places,        -  -     55 

81.  The  absorption  of  Radiant  Heat,         -  56 

82.  The  absorption  of  Hsat  affected  by  Color,  -            -     57 

83.  Transmission  of  Radiant  Heat,  57 

84.  Transmission  of  Heat  depends  upon  the  source  from  which  it 

proceeds,       ....                         -  -           58 

85.  Transmission  of  Heat  from  different  sources  of  equal  intensity, 

different  for  the  same  substance,      -  59 

86.  Transmission  of  Radiant  Heat  from  the  same  source,  different 

for  ditfcrent  substances — Diathermancy,      -            -  -           61 

87.  Diathermancy  not  proportioned  to  Transparency,  -    62 

88.  Melloni's  experiments  on  diathermancy  of  Solids,      -  62 

89.  The  diathermancy  of  Liquids,        -  -     64 

90.  The  diathermancy  of  Gases,    -                         -  65 

91.  Diathermancy  explained  on  the  supposition  that  there  are  differ- 

ent kinds  of  Heat,    -  66 

92.  The  existence  of  different  kinds  of  Heat  proved,  -  -    66 

93.  The  different  kinds  of  Heat  separated  from  each  other,  69 

94.  Different  kinds  of  Heat  emitted  by  different  sources  of  Heat,       -     70 


Xll  TABLE    OF    CONTENTS. 


'  95.  Unequal  diathermancy  of  Heat  from  different  sources,due  to  the 

different  kinds  of  Heat  emitted,                                                    -  72 

96.  Unequal  diathermancy  of  Heat  from  the  same  source,  owing  to  a 

property  in  bodies  caMcd  Thermo  chrosis,          -  -72 

97.  The  refrangibility  of  rays  of  heat  may  be  altered  by  re  radia- 

tion, —  Calorescence,        -                                                               -  74 

98.  The  double  refraction  and  polarization  of  Heat,        -  75 

99.  The  different  processes  through  which  Heat  may  pass  in  seeking 

an  Equilibrium,        -                                      ...  76 

EXPERIMENTS   ON   DIFFUSION   OF   HEAT,  —  76,  77,  78,  79. 
§  II.  Effects  of  Heat,  -Expansion. 

100.  Expansion  produced  by  Heat,       -            -            -            -            -  79 

101.  Expansion  of  Solids  proved,  -----  80 

102.  The  expansion  of  Solids  unequal,            -            -            -            -  80 

103.  The  expansion  of  Metals,                                 ...  81 

104.  The  force  of  Expansion,  -         -  »  .                 •  ••»'           .            .  81 

105.  Illustrations  of  Expansion,  •:*•••*.':       .*           v  '       -V           .  83 

106.  The  force  of  Contraction  equal  to  that  of  Expansion,     -            -  83 

107.  Applications  in  the  Arts,        -         .r.            .        '  •  i-           ..  ••  85 

108.  Injurious  effects  of  Expansion,     -            -           "•>-•••  '••    »'r'        .  86 

109.  Glass  fractured  by  Expansion,            ....  86 

110.  Fracture  produced  by  sudden  cooling,      -            -            -            -  87 

111.  Metallic  instruments  injured  by  Expansion,  88 

112.  Harrison's  Compensation  Pendulum,        -            -            -            -  88 

113.  Other  Compensation  Pendulums,      -                         -  89 

114.  The  Compensation  Balance,                       -                                      -  90 

115.  The  expansion  of  Liquids,      ...  .91 

116.  The  expansion  of  different  Liquids  unequal,       -                         -  91 

117.  The  expansion  of  the  Liquids  produced  by  the  condensation  of 

the  Gases,                                                                                         -  92 

118    The  expansion  of  Gases,        -  92 

119.  The  expansion  of  Air,      -                         -                                      -  92 

120.  The  expansion  of  Air  the  cause  of  the  draught  of  chimneys,  93 

121.  Exception  to  the  general  law  of  expansion  by  heat;  —  Water  at 

certain  temperatures  contracts  from  Heat  and  expands  from 

Cold,       -                                                                                         -  95 

122.  Important  effects  of  this  exception,    -  96 

123.  This  peculiar  constitution  of  water  proved  by  experiment,         -  97 


TABLE    OF    CONTENTS.  Xlll 


PAR. 

124.  Water  expands  in  freezing,  •  •  -98 

125.  Illustrations  of-  this  Force  in  Nature,  99 

126.  Other  substances  also  expand  in  Solidifying,     -                          -  100 

127.  The  Thermometer,    -  100 

128.  The  Air  Thermometer,  -                                                                -  101 

129.  The  Differential  Thermometer,         -  102 

130.  The  Mercurial  Thermome  er,      -                                                   -  103 

131.  Construction  of  the  Thermometer,   -  104 

132.  Fahrenheit's  Scale,                                                                              -  105 

133.  Other  Thermometric  Scales,  106 

134.  Different  forms  of  the  Thermometer,      -                                      -  108 

135.  Register  Thermometers,        -  108 

136.  Metallic  Thermometers,  -                                                                  -  109 

137.  Pyrometer.,,  -  110 

EXPERIMENTS;  EFFECTS  OF  HEAT,—  EXPANSION,—  110,  111,  112. 
§  III.  Effects  of  Heat,—  Liquefaction. 

138.  Heat  of  Composition,      -                                                             -  112 

139.  Liquefaction  produced  by  Heat,  —  melting  point,      -  113 

140.  Disappearance  of  a  large  amount  of  Heat  during  Liquefaction,  113 

141.  The  amount  of  Heat  absorbed  during  the  melting  of  Ice,  -  114 

142.  The  amount  of  Heat  thus  absorbed,  shown  by  experiment,       -  115 

143.  The  Heat  of  Fluidity,  115 

144.  Solids  cannot  be  heated  above  their  point  of  fusion,  until  the  . 

whole  of  the  solid  is  melted,  116 

145.  The  Heat  absorbed  in  Liquefaction  is  given  out  in  solidification,  117 

146.  Liquefaction  always  produces  a  reduction  of  Temperature,  118 

147.  Freezing  Mixtures,                                                                           .  119 

148.  Salts  and  Acids  dissolved  in  Water  lower  the  freezing  point,  120 

149.  Two  substances  mixed,  often  melt  at  a  lower  temperature  than 

either  separately,  —  Fluxes,              -  121 

150.  Refractory  Substances,     -            -            -            -                         -  121 

151.  Facility  of  Liquefaction  proportioned  to  the  quantity  of  Latent 

Heat  required,  -                                                                             -  122 

152.  Important  results  in  Nature  of  the  absorption  of  Heat  in  Lique- 

faction, and  its  evolution  in  Solidification,       -                         -  123 

153.  The  beneficial  effects  of  this  Constitution,  -  124 
J54.  Dr.  Black,  the  discoverer  of  the  Laws  of  Latent  Heat,  -            -  124 


XIV  TADLE    OF    CONTENTS. 

PAR.  PAQK. 

EXPERIMENTS  J   EFFECTS    OF    HEAT, — LIQUEFACTION,— 125,  126 
§  IV.  Effects  of  Hsat,— Ebullition. 

155.  Vaporization,       -  -  126 

156.  The  physical  properties  of  Vaj  ors,  -  127 

157.  Difference  between  Evaporation  and  Ebullition,  -  127 

158.  Ebullition,     -  127 

159.  Absorption  of  Heat  in  Ebullition,  -  128 

160.  The  heat  absorbed  in  Vaporization  given  out  again  in  Condensa- 

tion,      -  -  -  129 

161.  The  amount  of  Heat  absorbed  not  the  same  for  all  Vapors,  130 

162.  The  Boiling  point  variable, — influenced  by  atmospheric  pressure,  131 

163.  Wollaston's  Hypsometer,      -  133 

164.  Influence  of  adhesion  on  the  boiling  point,         -  -  -  133 

165.  Air  dissolved  in  Water  favors  Ebullition,    -  134 

166.  Solids  dissolved  in  a  Liquid  elevate  its  boiling  point,     -  -  134 

167.  Increase  of  pressure  elevates   the   boiling  point,— Diminished 

pressure  lowers  it,  -     135 

168.  Elevation  of  the  boiling  point  indicates  increase  of  pressure,         135 

169.  The  culinary  paradox, — Water  made  to  boil  by  the  application 

of  Cold,      -  137 

170.  The  amount  of  expansion  of  Liquids  in  Vaporization,  especially 

Water,  in  producing  Steam,  138 

171.  The  Condensation  of  Steam  by  decrease  of  Temperature,        -  139 

172.  Wollaston's  Steam  Bulb,      -  140 

173.  The  Steam  Engine,          -  -  140 

174.  The  two  forms  of  the  Steam  Engine,  142 

175.  The  Condensing  and  Non-condensing  Engine,   -  -  142 

176.  The  Steam  Engine  in  its  most  complete  form,         -  143 

177.  Latent  Heat  of  the  Condensing  Engine,  -  145 

178.  The  Boiler,    -  1-^ 

179.  The  Boiler  is  an  apparatus  for  forming  and  compressing  Steam,  147 

180.  Law  of  the  propagation  of  pressure  through  Fluids,  149 

181.  Mode  in  which  pressure  is  transmit  led  from  the  Boiler  to  the 

Cylinder,    -  1™ 

182.  Explosion  of  Boilers,      -  -     150 

183.  The  Boilers  of  Locomotives,  152 

184.  The  alternating  movement  of  the  Piston,  how  produced.     The 

Valves,        -  153 

185.  Steam  may  be  used  expansively,  -     155 

186.  The  expansive  power  of  Steam  increases  with  its  Temperature,    155 


TABLE    OF    CONTENTS.  XV 

PAR.'  PAGE. 

187.  No  economy  of  fuel  in  boiling  "Water  at  a  low  Temperature,    -     156 

188.  No  economy  in  using  Liquids  which  boil  at  a  lower  Temperature 

than  Water,       -  -     153 

189.  Super-heated  Steam,  153 

190.  Papin's  Digester,                                                    -  -     159 

191.  The  Spheroidal  state,  -  160 

192.  The  Spheroidal  state  explains  the  explosions  of  Boilers,  -     1G2 

193.  Distillation,   -  1G4 

194.  Uses  of  Distillation,         -  -     1GG 

195.  The  separation  of  two  Liquids  by  Distillation,  -  -           166 

EXPERIMENTS;    EFFECTS  OF  HEAT, — EBULLITION, — 167,168,169. 
§  V.  Effects  of  Heat,— Evaporation. 

196.  Evaporation,        -  -     169 

197.  Evaporation  takes  place  at  ordinary  Temperatures.     Heat,  its 

cause,     -  -     169 

198.  The  amount  of  Vapor  formed,  and  its  elasticity  proportioned  to 

Temperature,    -  ...     170 

199.  These  truths  illustrated  by  Experiment,      -  -  171 

200.  The  rapidity  of  Evaporation  varies  with  the  pressure.     In  a 

vacuum  it  is  instantaneous,  -  172 

201.  The  amount  of  Evaporation  of  different  Liquids  in  a  vacuum  at 

the  same  Temperature,  is  unequal,  1 73 

202.  The  elastic  force  of  Vapor  in  a  confined  space  does  not  vary  with 

pressure,  but  with  Temperature,    -  174 

203.  The  elastic  force  of  Vapor  in  two  connecting  vessels  cannot  rise 

above  the  elastic  force  proper  to  the  colder  vessel,  177 

204.  The  rate  of  Evaporation  of  different  Liquids  in  Air  is  unequal,     179 

205.  The  presence  of  Vapor  in  Air  affects  its  bulk  and  density,  ISO 

206.  The  circumstances  which  influence  Evaporation,  -     181 

207.  Absorption  of  Heat,— diminution  of  Temperature  produced  by 

Evaporation,      -  -     181 

208.  Removal  of  Atmospheric  Pressure  hastens  Evaporation,  and  in- 

creases Cold,      -  -     183 

209.  Cause  of  the  Cold  produced  by  Evaporation,  18 1 

210.  The  Cryophorus,  -     184 

211.  The  Pulse  Glass,       -  186 

212.  The  cold  of  Fountains  and  Earthcrn  water  jars,  -     186 

213.  Effect  of  Evaporation  on  Animal  life,  18G 

214.  Effect  of  Evaporation  on  Climate,           -  -            -            -     187 


XV111  TABLE    OF    CONTENTS. 

PAR.  PAGE. 

264.  The  convertibility  of  the  Forces,  and  their  indestructibility,    -    244 
264*.  There  is  an  analogy  between  Heat,  Light,  and  Sound,      -          245 

CHAPTER   III. 

THE    SECOND    CHEMICAL    AGENT, LIGHT. 

THE  NATURK  OF  LIGHT  ;  SOURCES  ;  REFLECTION  J  REFRACTION  ;  SOLAR 
SPECTRUM;     SPECTRUM    ANALYSIS;     EFFECT    OF    LIGHT    ON 
PLANTS  ;   CHEMICAL  EFFECT  OF    LIGHT  ;   PHOTOGRA- 
PHY J       RELATIONS      OF       LIGHT      AND     HEAT. 

265.  The  nature  of  Light,       ...  -    246 

266.  The  sources  of  Light, — Solar  Light,            -                         -  247 

267.  The  ignition  of  Solids  a  source  of  Light,           -  -    247 

268.  Electricity  a  source  of  Light,  248 

269.  Exposure  to  the  Sun's  rays  and  to  Electricity  a  source  of  Light,  249 

270.  Decaying  Animal  and  Vegetable  matter  a  source  of  Light,  249 

271.  Luminous  animals  a  source  of  Light,     -  -    249 

272.  Crystallization  a  source  of  Light,     -                         -  249 
270.  The  reflection  of  Light,  "-  -    25!) 

274.  The  refraction  of  Light,        -"  251 

275.  The  double  refraction  and  polarization  of  Light,  .  -    252 

276.  The  compound  nature  of  Solar  Light.     The  illuminating  rays,     253 

277.  The  number  of  vibrations  required  to  produce  the  different  col- 

ors of  the  Solar  Spectrum,  256 

278.  The  Heat  rays  of  the  Solar  beam,  -    256 

279.  The  Chemical  rays  of  the  Solar  beam,  -                                     258 

280.  The  range  of  the  Chemical  rays  in  the  Solar  Spectrum, — Fluor- 


escence, 


259 


281 .  The  triple  character  of  Solar  Light, 

282.  The  spectra  produced  by  Artificial  light  and  colored  flames,  262 

283.  The  Solar  Spectrum  not  continuous,  but  crossed  by  fixed  dark 

lines,— Fraunhofer's  Lines, 

284.  Spectra  produced  by  the  light  of  the  Nebulae,  and  by  Artificial 

light,  crossed  by  bright,  instead  of  dark,  lines,      - 

285.  Spectrum  Analysis, 

286.  The  Spectroscope,      - 

287.  The  new  metals  discovered  by  Spectrum  Analysis, 

288.  The  dark  lines  of  the  Solar  Spectrum  exactly  coincident  with 

the  bright  lines  of  spectra  produced  by  the  metals,      -  -     -71 


TABLE    OF    CONTENTS.  XIX 

PAR.  PAGE. 

289.  The  dark  lines  of  the  Solar  Spectrum  explained,  -    272 
289*.  The  Solar  Specturm  sometimes  crossed  by  bright  lines,  -          273 
290*.  Spectra  of  the  Moon  and  Planets.     291*.  Of  the  Stars,  275 
292*.  Spectra  of  the  Nebulae.     293*.  Spectra  of  Comets,  -           276 
294*.  Spectra  of  the  Aurora  Borealis,  and  of  Lightning,     -  276 

290.  Effects  of  Light  on  Vegetation.     291.  Summary  of  these,     277,  278 

292.  The  effects  of  Solar  Light  on  Chemical  compounds,     -  -     279 

293.  The  Daguerreotype  process.     294.  The  Photograph,          -  280,  281 

283.  The  Photographic  Camera,  283 

284.  Photographs  are  produced  solely  by  the  Chemical  rays.  -     284 

297.  Practical  importance  of  distinguishing  between  the  Illuminating 

and  Chemical  rays  of  Light,     -  -    2^5 

298.  All  surfaces  are  affected  by  the  Sun's  light,  286 

299.  The  relations  of  the  rays  of  Heat,  Light  and  Chemical  effect,  in 

the  Solar  Spectrum,      -  -    287 

EXPERIMENTS  ON    LIGHT, — 287,  288,  289. 

CHAPTER  IV. 

THE    THIRD    CHEMICAL    AGENT, ELECTRICITY. 

STATICAL   ELECTRICITY;    GALVANIC   ELECTRICITY;  ELECTRO-MAGNET- 
ISM ;     MAGNETO-ELECTRICITY  J      THERMO-ELECTRICITY  ;     ANIMAL 
ELECTRICITY  J    THE  RELATIONS  OF  THE    CHEMICAL  AGENTS. 

§  I.  Statical  Electricity. 

300.  Electricity,  .  ...  289 

301.  The  nature  of  Electricity,     -  290 

302.  The  fundamental  facts  of  Statical  Electricity,     -  290 

303.  The  sources  of  Electricity,    -  291 

304.  Electrical  attraction  and  repulsion,          ....  292 

305.  Two  bodies  similarly  electrified  repel  each  other,     -  -  293 

306.  Two  bodies  differently  electrified  attract  each  other.     Two  kinds 

of  Electricity, — Vitreous  and  Resinous,    -  293 

307.  The  Electroscope,  -    293 
303.  Conductors  and  Non-conductors, — Insulation,          -            -  294 

309.  Vitreous  electricity  cannot  be  produced  without  a  corresponding 

amount  of  Resinous  electricity,  and  vice  versa,      -  -  295 

310.  Induction  of  Electricity,  ...    296 

311.  The  intervention  of  solid  matter  no  obstacle  to  Induction,  -  297 


XX  TA3LE    OF    CONTENTS. 


PAB. 


PAGS. 


312.  The  theory  of  Induction,  -  ....  ^98 

313.  Electricity  confined  to  the  external  surface  of  bodies,          -  299 

314.  Theories  of  Electricity,   -  -  ...  390 

315.  Development  of  large  quantities,— The  Electrical  Machine,  301 

316.  The  Ley  den  Jar,  .....  302 

317.  Mode  of  charging  the  Leyden  Jar,  ....  304 

318.  The  theory  of  the  Leyden  Jar,   -  ....  304 

319.  The  Electrophorus,    -  -  .  305. 

320.  The  Hydro-Electric  Machine,     -  -  -  -  306 

321.  The  effects  of  Electricity,    -  -  -  .  .  307 

EXPERIMENTS   ON    STATICAL    ELECTRICITY,— 296,  297. 
II.  Galvanic  Electricity.  .    . 

322.  Galvanic  Electricity,        -                                      -           *"  •      "•    311 

323.  Discovery  of  Galvanic  Electricity,    -            -            .  .  „.„ 

324.  Galvani's  theory,              -            -            -            .            .  "312 

325.  Correction  of  Galvani's  theory,  by  Volta,    -  -  313 

326.  The  Voltaic  Pile,          ;-  ?            -                                      .  .    gu 

327.  True  theory  of  the  Pile,       -                      >*•-..-•••  .  315 

328.  Chemical  constitution  of  the  substances  used  to  produce  Voltaic 

Electricity,  -  316 

329.  Proof  that  Chemical  decomposition  is  the  source  of  Galvanic 

Electricity,  -  -  317 

330.  The  decomposing  plate  is  the  point  of  departure  of  the  Electrical 

current,       ....  -  318 

331.  Mode  of  transfer  of  the  Hydrogen,         -  -  -  319 

332.  The  part  played  by  the  Copper  plate,  -  320 

333.  The  polarization  and  transfer  of  the  elements  of  the  Liquid,  and 

the  polarization  of  the  Solid  particles  of  the  circuit,  necessary 
for  the  electric  force  to  circulate,  -     321 

334.  Proof  that  a  state  of  electrical  Tension  exists  in  the  plates  before 

the  actual  passage  of  the  current,        -  -     323 

335.  The  energy  of  the  current  proportionate  to  the  Chemical  activity,  324 

336.  The  direction  of  the  current  dependent  upon  the  direction  of  the 

Chemical  action,      -  325 

337.  Direct  metallic  connection  between  the  generating  and  conduct- 

ing plate,  not  necessary,     -  326 

338.  Effect  of  the  discharge  of  Hydrogen  on  the  conducting  plate,  -  326 

339.  The  Gas  Batterv,      -  327 

340.  The  Galvanic  Battery,    -  «  -  -  »  -  329 


TABLE    OF    CONTENTS.  XXI 


PAR. 

341.  Batteries  of  Intensity,  and  Batteries  of  Quantity,         •  -    330 

342.  Improved  Batteries,  -  -  331 

343.  The  Sulphate  of  Copper  Buttery,  -    332 

344.  Daniell's  Battery,      -  333 

345.  Grove's  Battery,  -  -  .  .    335 

346.  Bunsen's  Battery,      -  336  j 

347.  Smce's  Battery,    -  -  -     337 

348.  Management  ol  Batteries.     -  -  337  I 
349    De  Luc's  Pile,—  the  dry  Pile,      -                                                   -     339 

350.  'Proof  of  the  similarity  of  the  electricity  of  the  Battery  and  that 

of  the  Electrical  Machine,  -  340 

351.  The  difference  between  Galvanic  and  Statical  Electricity,          -     3^1 

352.  Galvanic  Batteries  of  Historic  note,  341 

353.  Heating  effects  of  the  Galvanic  current,  -     343 

354.  Ignition  produced,     -  -  343 

355.  Luminous  effects,  ...  .  344 

356.  Duboscq's  Electric  Lamp,     -  -  345 

357.  Discovery  of  the  Electric  Light,  -     346 

358.  The  Electric  Light  not  the  result  of  Combustion,   -  346 

359.  The  properties  and  intensity  of  the  Electric  Light,        -  -     347 

360.  Connection  between  the  heat  of  the  battery  and  the  Mechanical 

equivalent  of  Heat,       -  -  347 

361.  Heating  effects  are  best  produced  by  batteries  of  Quantity,  343 

362.  The   Chemical   effects  of  the   Galvanic  current,  —  decomposing 

power,         -  -  348 

363.  The  constitution  of  Water,          -  -     348 

364.  The  decomposition  of  Water  by  the  Battery,  349 

365.  The  decomposition  of    Water  is    effected  by  the   polarization 

and  transfer  of  its  component  elements,     -  350 

366.  The  decomposition  of  other  compound  Liquids,  -     352 

367.  The  decomposition  of  Metallic  Oxides  in  .solution,  352 

368.  The  decomposition  of  Metallic  Salts  in  solution,  -     353 

369.  The  decomposing  Tube,        -  -  353 

370.  The  Glass  Cup  with  porous  diaphragm,  •     354 

371.  Secondary  decomposition,     -  -  355 

372.  The  experiment  of  three  cups  connected  by  Syphons,    -  -     357 

373.  Sir  H.  Davy's  experiment  in  which  the  Acids  and  Alkalies,  under 

the  influence  of  the  current,  seem  to  lose  their  ordinary  affinity,  358 

374.  Exception  in  the  case  of  the  production  of  insoluble  compounds,  358 

375.  The  successive  action  of  the  same  current  on  different  vessels  of 

Water,        .......  359 


XXII  TABLE    OF    CONTENTS. 

PAR.  PAGE. 

376.  The  successive  action  of  the  same  current  on  vessels  containing 

different  compound  Liquids.     -  -    360 

377.  Electro-Negative  bodies,        -  361 

378.  Electro-Positive  bodies,   -  -    361 

379.  The  Law  of  Chemical  decomposition  by  the  electrical  current,    361 

380.  The  amount  of  Zinc  dissolved  from  the  generating  plate,  is  pro- 

portioned to  the  amount  of  Chemical  decomposition  produced, 
and  vice  versa,    -  -    362 

381.  The  Voltameter,        -  362 

382.  Electro-plating  and  gilding,         -  -    36'J 

383.  Electrotyping,  364 

384.  The  protection  of  the  Copper  sheathing  of  ships,  -    366 

§  III.  Electro-Magnetism. 

3S5.  Magnetic  effects  of  the  current,  -  -    3671 

386.  What  is  a  Magnet  ?   -  369 

387.  The  poles  of  the  Magnet,  -    369 

388.  The  mutual  actions  of  the  Poles,      -  369 
289.  The  directive  action  of  the  Earth  upon  the  Magnet,  -            -    370 

390.  The  Astatic  Needle,  -  371 

391.  The  induction  of  Magnetism,      -  -    372 

392.  All  substances  are  either  attracted  or  repelled  by  the  Magnet, — 

Magnetic  and  Dia-magnetic  bodies,      -  -    372 

393.  The  dia-magnetism  of  Gases,  373 

394.  Oxvgen,  a  magnetic  substance,   -            -  -    374 

395.  Magnetic  and  Dia-magnetic  bodies,  -  375 

396.  Reason  why  a  magnetic  needle  assumes  a  position  at  right  an- 

gles to  the  conducting  wire,  375 

397.  The  Galvanic  current  produces  magnetism, — Electro-magnets,      376 

398.  Molecular  movements  during  the  magnetization  of  bars,     -  378 

399.  The  Galvanometer,          -  -378 

400.  The  Astatic  Galvanometer,  -  379 

401.  The  Liquid  part  of  the  Voltaic  circuit  acts  upon  the  magnetic 

needle,  -                                                 -  -    380 

402.  The  Laws  of  Electro-magnetism,      -  -     381 

403.  Ampere's  Theory  of  magnetism,  -     381 

404.  The  magnetic  effect  of  the  wire  carrying  the  current  accounted 

for  by  Ampere's  theory,  -     383 

405.  The  most  powerful  form  of  Electro-magnets,— the  Horse  Shoe 

Magnet,  -     386 

406.  The  Magnetic  Telegraph,     -  387 

407.  Morse's  Electro-magnetic  Indicator,        -  •  -    390 


TABLE    OF    CONTEXTS.  Xxiii 

PAR.  PAGE. 

408.  The  Telegraphic  manipulator,  and  Morse's  alphabet,    -         -  391 

409.  The  Relay.     409*.  M  ssages  sent  by  breaking  the  circuit,  393,  394 

410.  The  transmission  of  messages,    -                                                     -  395 

411.  Telegraphic  Batteries,  396 

412.  Caillaud's  Battery,                                                                               -  397 

413.  The  Sand  Battery,    -  398 

414.  The  Earth  as  a  part  of  the  Telegraphic  circuit,                           -  398 

415.  The  velocity  of  the  telegraphic  current,        -                         -  401 

416.  The  Submarine  Telegraph,          -                                                     -  401 

417.  The  Atlantic  Telegraph  Cable,          -  403 

418.  Thomson's  Reflecting  Galvanometer,      -                                      -  405 

419.  The  actual  arrangement  of  the  Cable,                                    •  406 
4"20.  The  Rate  of  transmission,                                                              -  407 

421.  History  of  the  Atlantic  Telegraph,  -  40S 

422.  Application  of  Electro-magnetism  to  th3  production  of  Motion,  409 

423.  The  Electro-motor  of  M.  Fromcnt,  -  410 

424.  The  Electromotor  of  M.  Jacoby,                         -                         -  412 

425.  Electro  magnetic  Locomotives,         -            -                         -  412 

426.  Page's  Electro-magnetic  Locomotive,      -             -                          -  412 

427.  Stewart's  Electro-motor,       -  414 

428.  The  expense  of  Electro-magnetism  compared  with  Steam,        -  414 

429.  Electro  magnetic  Clocks,       -  41  *i 

430.  The  Electric  Fire-alarm,  -                                                   -            -  417 

431.  Electric  Gas-lighting,                           -                                       -  420 

432.  Progress  of  discovery  in  Electro  magnetism,      -            -  421 

§  IV.  Galvanic  Induced  Electricity. 

433.  Volta-electric  Induction,                           ....  403 

434.  Faraday's  Experiments,         -                                                  -  4^5 

435.  The  inductive  effect  of  the  Primary  current  often  takes  place 

through  a  considerable  distance,     -  427 

436.  Induction  of  a  momentary  Secondary  current  by  the  approach 

and  removal  of  the  primary  current,          -            -  429 

437.  The  conditions  of  Induction,  and  properties  of  induced  currents,  431 

438.  Induction  of  a  current  on  itself     The  extra  current,          -  431 

439.  Induction  of  a  Secondary  current  in  the  primary  wire  itself,  433 

440.  Induced  Tertiary  currents.     Henry's  Coils,        -                          -  436 

441.  History  of  the  discovery  of  Volta-electric  Induction,          -  438 

§  V.  Magneto-Electricity. 

442    Magneto  electric  Induction,         -                                      -            -  439 

443.  Electricity  induced  by  induced  magnetism,               -            -  44U 


TABLE    OF    CONTENTS. 

PAR.  PAGE. 

444.  History  of  the  discovery  of  Magneto-electricity,  •  •    442 

445.  Volta-Magneto-electric  Induction,     ....  443 

446.  History  of  the  discovery  of  the  Induction  of  Electricity  by  Elec- 

tro-magnetism,       -  -  444 

447.  Arago's  Rotations,          ...  .     443 

448.  The  magnetism  of  the  Earth  induces  secondary  currents  of  EJec- 

tricity  in  metallic  bodies  in  motion,     -  -  448 

449.  Magneto-electric  Induction  confirms  Ampere's  Theory,       -  449 

450.  Volta-Magneto-electric  Coils  for  inducing  secondary  currents,  •  449 

451.  Page's  Separable  helices,       ....  459 

452.  The  Circuit-breaker,        -  -  *  452 

453.  Ruhmkorff's  Coil  for  inducing  secondarv  electrical  currents,  454 
453*.  The  Condenser.    454.  Ruhrnkorff 's  Coil  complete,    -        456,  458 

455.  Ritchie's  improved  Ruhmkorffs  Coil,        ...  459 

456.  The  management  of  Ruhmkorff's  Coil,  -  -    462 

457.  The  mechanical  effects  of  Ruhmkorff's  Coil,           -            -  464 

458.  The  Physiological  effects,  -     464 

459.  The  Heating  effects,  -                                      -            -            -  464 

460.  The  Luminous  effects,    -            -            -            -            -  -466 

461.  The  Light  intermittent,  and  affected  by  the  Magnet,           -  470 

462.  Application  of  Geissler's  Tubes  to  medical  purposes,  and  to  the 

illumination  of  Mines,       -  -  472 

463.  Application  of  Ruhmkorff's  Coil  to  Spectrum  Analysis,  -  473 

464.  Chemical  effects,        -  474 

465.  Conversion  of  Carbon  into  the  Diamond  by  the  long  continued 

action  of  the  Coil,  -  -  -  »•  -  477 

466.  Magneto-electric  Machines.     The  principles  on  which  they  de- 

pend, .......  477 

467.  Saxton's  Magneto-electric  Machine,        -  -  480 

468.  Page's  Magneto-electric  Machine,     -  483 

469.  Magneto  electricity  used  in  the  Arts  in  place  of  Voltaic  electric- 

ity, especially  for  the  illumination  of  Light-houses,  485 

470.  Holmes'   Magneto-electric    Machine,   for    illuminating    Light- 

houses,       ...  -  -  488 

471.  Wilde's  Magneto-electric  Machine.     469*.  Improvements  of,  4 ; 9,  495 
470*.  Siemens'  and  Wheatstones  Machines,  -  -     496 
471*.  Ladd's  first  Machine.     472*.  Ladd's  second  Machine,      -  497,  498 

473.  Difference  between  the  electricity  of  the  machine  and  battery,      500 

474.  Points  of  resemblance  between  the  electricity  of  the  Machine 

and  the  secondary  electrical  currents  induced  by  the  primary 
current,  and  by  Magnets,  •  •    502 


TABLE    OF    CONTENTS.  XXV 

PAH.  PAGE. 

475.  The  quantity  of  electricity  produced  by  the  Battery  immense, 

and  its  magnetic  effect  far  superior  to  that  of  the  Machine,         £02 
47G.  The  action  of  electricity  and  magnetism  on  Light,        -  -     504 

477.  Progress  of  discovery  in  the  induction  of  electricity,  and  the 

construction  of  Induction  Coils  and  Magneto-electric  Machines,  508 

§  VI.  Thermo-Electricity. 

478.  Heat  produces  Electricity,           -  -  -     510 

479.  Thermo-electric  Battery,       -                          -  512 

480.  Thermo-electric  Battery  of  Nobili,          -            -  -  ~    513 

481.  Thermo-multiplier  of  Melloni,          ...  514 

482.  Farmer's  Thermo-electric  Battery,          -            -  -  .515 

§  VII.  Animal  Electricity. 

483.  Animal  life  produces  Electricity,      -  -  -  .  517 

484.  Physiological  effects  of  the  Galvanic  current,     -  -  -     519 

485.  Various  sources  of  Electricity,  and  its  relations  to  the  other  two 

Chemical  Agents,  Heat  and  Light,      -  -     522 

§  VIII.  Conclusion  of  the  Chemical  Forces. 

486.  The  relations  subsisting  between  the  three  Chemical  Forces, 

Heat,  Light  and  Electricity.     They  are  convertible,  and  prob- 
ably due  to  the  motion  of  the  molecules  of  bodies,      -  -    523 

487.  In  every  case  of  the  convertibility  of  the  Chemical  Forces,  there 

is  an  expenditure  of  the  original  Force,  and  a  reduction  of  its 
strength  exactly  equivalent  to  that  of  the  new  Force  produced,  525 

488.  The   convertibility  and   equivalency  of  Forces  true  of  all  the 

Forces  which  act  on  Matter,  528 

489.  The  Indestructibility  and  Conservation  of  Force.     The  Correla- 

tion of  The  Forces,  528 

490.  Heat  and  Electricity  the  chief  agents  used  by  the  Chemist  in  his 

investigations.     The  Lamp  and  the  Galvanic  Battery  his  chief 
instruments,       -  .  •     529 

491.  The  Conclusion  of  the  Chemical  Forces,     -  530 

EXPERIMENTS  ON  GALVANIC  ELECTRICITY;  ELECTRO-MAGNETISM; 
MAGNETO-KLECTRICITY  ;  RUIIMKORFF's  COILJ  THERMO-ELECTRICITY, 
AND  ANIMAL  ELECTRICITY, — 

531,  532,  533,  534,    535,    536,  537,   538,    539,    540,541,  542,  543. 


I/I   JS 

U  N  1  V  K  1  -I  S  IT  V    O  K 

CALIFORNIA. 


THE 


CHEMICAL    FORCES 


HEAT— LIGHT— ELECTRICITY. 


CHAPTER  I. 

SUBJECT-MATTER     OF     CHEMISTRY  :     USES  I     HISTORY  :     THE 
CHEMICAL,   AGENTS. 

1.  Origin  cf  the  name  Chemistry.     The  name  Chemistry, 
is  said  to  be  derived  from  the  Arabic  word  Kimia,  something 
hidden  or  concealed,  and  from  this,  to  have  been  converted  inlo 
Xi]fielut  a  word  first  used  by  the  Greeks  about  the  eleventh 
century,  and  meaning  the  art  of  making  gold  arid  silver.     Be- 
tween the  fifth  century  and  the  taking  of  Constantinople  in  the 
fifteenth  century,  says  Dr.  Thomson,  in  his  History  of  Chemis- 
try, the  Greeks  believed  in  the  possibility  of  making  gold  and 
silver  artificially;  and  the  art  which  professed  to  teach  these 
processes  was  called  by  them,  Chemistry.     This  idea,  however, 
has  long  since  been  thoroughly  discarded,  and  is  now  no  longer 
heard  of. 

2.  The  nature  of  Chemistry.    It  explains  the  composition 
of  Matter.     Chemistry  is  now   a  science  of   well-established 
laws  and  principles,  the  object  of  which  is  the  study  of  the 
composition  of  Matter.     It  informs  us  of  what  the  various  sub- 

1    What  is  the  derivation  of  the  name  Chemistry  ?    What  was  the  meaning  of  the 
•word  among  the  Greeks?    Is  it  any  longer  regarded  as  the  art  of  making  gold  and  sil- 
ver ? — 2    How  is  it  now  regarded  ?    Enumerate  its  objects. 
1 


2  PROPERTIES    OF    MATTER. 

stances  in  nature,  the  rocks,  the  soil,  the  water,  the  air,  the 
trees,  the  plants,  the  animals,  and  all  the  various,  solids  and 
liquids  of  the  earth  are  made.  It  teaches  us,  also,  the  number 
and  properties  of  these  elementary  substances,  and  the  action 
which  they  exert  upon  each  other  when  mingled.  It  studies  the 
laws  which  regulate  their  union,  ascertains  the  proportions  in 
which  they  combine,  devises  means  for  separating  them  when 
combined,  and  seeks  to  apply  such  knowledge  to  the  explanation 
of  the  phenomena  of  Nature,  and  the  improvement  of  the  va- 
rious Arts. 

3.  Matter,  what  it  is,      Chemistry,  it  will  be  seen,  treats  of 
the  subject  of  Matter.     The   question  therefore  arises,  What  is 
Matter?     The  name  Matter  may  be  given  to  any  substance 
which  is  cognizable  by  any  one  or  all  of  the  senses.     Every 
thing  not  cognizable  by  the  senses,  passes  under  tne  name  Im- 
material.    All  matter  possesses  the  four  properties  of  Extension, 
Impenetrability,  Inertia,  and  Weight.     We  know  that  a  body 
possesses  Extension,  froin  its  occupying  a  portion  of  space ;  we 
know  that  it  possesses  Impenetrability,  from  its  not  allowing 
another  body  to  occupy  this  space  at  the  same  time  with  itself; 
we  know  that  it  possesses   Inertia,  from  its  want  of  power  to 
change  its  state,  to  move  if  at  rest,  to  cease  to  move  if  in  mo- 
tion ;  we  know  that  it  possesses  Weight,  from  its  effect  upon  the 
balance,  and  from  the  fact  that  it  falls  to  the  ground  if  its  sup- 
port be  withdrawn. 

4.  Matter,  though  Inert,  capable  of  being-  affected  by  Ex- 
ternal Forces.     Matter  is  in  itself  inert,  but  it  is  subject  to  the 
control  of  certain  forces, — 1st.    Cohesion,     This  force  binds  to- 
gether particles  of  matter  of  the  same  kind,  with  more  or  less 
strength,  producing  solid  bodies  of  different  sizes,  and  various 
degrees  of  hardness  and  toughnessl     It  acts  only  at  insensible 
distances,  the  closest  proximity  of  the  particles  being  required  in 
order  to  admit  of  its  exercise.     When  this  proximity  has  once 
been  destroyed,  its  restoration  is  a  matter  of  great  difficulty. — 
2d.  Adhesion.     This  is  the  force  which  unites  unlike  particles 
of  matter,  when  brought  near  to  each  other.     Thus,  if  a  rod  of 
glass  be  dipped  in  water  or  oil,  particles  of  the  liquid  will  adhere 
to  its  surface.     In  common  language,  the  rod  is  said  to  have  be- 
come wetted ;  in  the  language  of  science,  adhesion  has  taken 
place  between  the  particles  of  glass  and  those  of  the  liquid  with 

3  Give  the  meaning  of  the  word  Maoter?  What  four  properties  does  it  possess? 
What  is  meant  by  Extension?  by  Impenetrability  ?  by  Inertia?  by  Weight? — 4. 
What  four  Forces  is  Matter  subject  to  ?  Define  Cohesion.  Define  Adhesion. 


STATES    OF    MATTER.  p 

which  it  has  been  brought  in  contact.  By  the  same  force, 
liquids  are  raised  in  fine  tubes,  provided  there  be  adhesion 
between  them  and  the  matter  of  which  the  tubes  are  made  ;  in 
such  cases,  it  constitutes  a  force  which  is  called  Capillary  At- 
traction. In  other  cases  it  is  the  force  which  operates  in  the 
use  of  cements  and  glue.  It  is  unlike  cohesion,  in  tending  to 
unite  particles  of  different  kinds,  and  in  not  requiring  such  close 
proximity  for  its  action. — 3d.  Repulsion.  This  is  the  force 
which  pi-events  particles  of  the  same  body  from  coming  into 
actual  c-mtact,  and  from  being  so  tightly  bound  together  by  the 
force  of  cohesion  as  to  be  incapable  of  separation.  It  is 
supposed  to  be  due  to  the  presence  of  heat  in  bodies,  and  is 
always  the  antagonist  of  cohesion.  The  state  of  a  body  as  to 
softness  and  hardness,  depends  upon  the  relative  proportion  exist- 
ing b  tween  these  two  forces.  When  repulsion  predominates,  the 
substan  -e  will  be  very  soft ;  but  when  cohesion  is  superior,  it  will 
become  proportijnally  hard  and  tough.  We  possess  the  means 
of  .increasing  an  1  diminishing  the  force  of  repulsion  in  any  sub- 
stance, aid,  co  is 3quently,  of  affecting  many  of  its  physical  prop- 
erties, by  elevating  or  depressing  its  temperature. — 4th.  Gravity. 
This  fbi-ci  operates  upon  particles  of  matter,  whether  like  or 
unlike,  and  tends  to  draw  them  toward  each  other.  It  does  not 
require  close  proximity  for  its  action,  though  its  power  is  in- 
creased as  the  square  of  the  distance  diminishes.  This  is  the 
force  which  tends  to  draw  masses  of  matter  towards  the  centre 
of  the  earth,  and  to  attract  the  earth  itself,  with  all  the  planets, 
to  the  sun.  It  is  not  confined,  however,  to  such  large  masses 
of  matter  as  these.  A  pendulum,  in  vibration,  will  be  sensibly 
affected  by  the  presence  of  a  mountain  in  its  neighborhood ;  and 
even  smaller  masses  of  matter,  if  susceptible  of  motion,  tend  to 
approach  each  other  under  its  influence. 

5.  The  Three  Principal  States  of  Matter :  Solid,  Liquid, 
and  Gaseous.  Matter  exists  in  three  principal  states,  the  Solid, 
the  Liquid,  and  the  Gaseous.  When  the  particles  of  a  body 
are  in  close  proximity,  and  so  firmly  united  as  to  be  incapable 
of  any  considerable  change  of  place  in  reference  to  each  other, 
the  body  is  said  to  be  a  Solid.  When  the  particles  are  far 
enough  apart  to  admit  of  a  very  appreciable  degree  of  motion, 
they  form  a  Liquid ;  and  when  they  are  separated  so  far 
as  to  cease  to  be  drawn  towards  each  other  at  all,  they  con- 
stitute a  Gas,  like  the  atmosphere,  or  a  Vapor,  like  steam. 

4.  Define  Repulsion.     Define  Gravity  —5.  State  the  three  principal  forms  of  Matter. 
State  the  difference  between  So.ids,  Liquids,  and  Gases. 


4  PROPERTIES    OF    SOLIDS    AND    LIQUIDS. 

The  difference  between  gases  and  vapors,  is  that  the  former  are 
permanently  aeriform  at  all  ordinary  temperatures,  the  latter 
are  the  aeriform  fluids,  that  are  formed,  by  the  addition  of  heat, 
from  various  liquids,  such  as  alcohol,  ether,  water,  and  mercury, 
and  they  remain  in  the  aeriform  state  only  so  long  as  their  tem- 
perature is  maintained  above  a  certain  point ;  when  their  tem- 
perature is  reduced  below  this  point,  they  immediately  return 
to  the  liquid  state  from  which  they  sprung. 

The  existence  of  matter  in  one  of  these  states  in  preference 
to  the  others,  is  chiefly  due  to  the  relative  strength  of  the  forces 
of  cohesion  and  repulsion.  When  Cohesion  predominates,  the 
body  is  in  the  solid  state :  when  the  two  forces  are  in  equilib- 
rium, the  body  is  in  the  liquid  state ;  and  when  Repulsion  pre- 
ponderates, the  body  assumes  the  gaseous  state.  As  we  have 
the  means  of  varying  the  force  of  repulsion  by  the  addition  or 
abstraction  of  heat,  oftentimes  the  same  portion  of  matter  may 
be  made  to  pass  from  the  first  of  these  states,  through  the  second, 
into  the  third,  and  then  to  return  to  its  original  condition.  Thus, 
ice,  by  the  application  of  heat,  may  be  converted  into  water ;  this 
water,  by  the  further  addition  of  heat,  into  steam  ;  and  when  this 
heat  is  withdrawn,  the  steam  will  return  first  into  the  state  of 
water,  and  then  into  that  of  ice.  In  the  same  way,  many  of  the 
permanent  gases,  by  the  combined  influence  of  the  abstraction 
of  heat,  and  mechanical  pressure,  may  be  reduced  to  the  liquid, 
and  finally  to~  the  solid  state. 

6.  The  Peculiar  Properties  of  Solids.     Solids  possess,  to  a 
marked  degree,  the   distinctive  properties  of  matter,   such  as 
Opacity,  Transparency,  Softness,  Hardness,  Elasticity  or  the  re- 
verse,  Color,  and  Density.      Their  particles  are  also  nearly 
immovable,  and  pressure  operating  upon  them  is  propagated 
through  them  in  right  lines,  or  in  a  right  line  which  passes  through 
their  centres  of  gravity. 

7.  The  Peculiar  Properties  of  Liquids.    Liquids  exhibit  the 
characteristic  properties  of  matter  with  less  positiveness  than 
Solids.     They  are  all,  with  the  exception  of  mercury,  more  or 
less  transparent.     They  are  compressible  only  to  a  very  lim- 
ited extent,  and,  therefore,  very  slightly  elastic.     They  differ 
from  solids,  in  propagating  pressure,  made  at  any  one  point,  equal- 
ly in  all  directions ;  consequently,  a  pressure  of  one  pound  to 
the  square  inch,  upon  the  side  or  bottom  or  any  part  of  a  liquid, 

5.  To  whit  is  this  difference  owing?  Show  the  effect  of  increasing  and  diminishing 
the  force  of  repulsion  in  the  case  ot  Ice. — 6.  State  the  peculiar  properties  of  Solids. 
How  is  pressure  propagated  through  them  1 — 7.  State  the  peculiar  properties  of 
Liquids.  Show  how  pressure  is  propagated  through  them. 


PROPERTIES    OF    GASES.  5 

will  be  propagated  in  such  a  way  that  the  same  pressure  of  one 
pound  will  be  experienced  by  every  other  square  inch  throughout 
the  liquid,  and  by  every  square  inch  or  the  vessel  containing  it. 
The  weight  of  a  solid  immersed  in  a  liquid  is  diminished  by 
the  weight  of  the  mass  of  liquid  which  it  displaces.  All  liquids 
therefore  have  a  certain  buoyant  power.  Water  is  taken  as  the 
type  of  liquids,  because  it  possesses  their  marked  characteristics 
in  an  eminent  degree. 

8.  The  Peculiar  Properties  of  Gases.     Gases  possess  the 
distinguishing  properties  of  matter  to  a  much  less  extent  than 
either  Solids  or  Liquid-;.     They  are  all  transparent,  and  many 
of  them  colorless ;  their  particles  are  capable  of  an  unlimited 
degree  of  motion ;  they  are  very  compressible,  and  highly  elas- 
tic, and  tend,  when  compressed,  to  return  with  great  force  to 
their  original  dimensions.     As  they  are  in  a  state  of  constant 
compression,  in  consequence  of   the  atmospheric   pressure  to 
which  they  are  always  subjected,  they  are  never  in  a  state  of 
permanent  equilibrium,  but  are  continually  striving  to  increase 
in  volume,  and  tending  powerfully  to  expand.     This  is  their 
principal   characteristic.     They  are  greatly  dilated   by    heat; 
pressure  is  propagated  through  them,  as  through  liquids,  equally 
in  all  directions ;  some  of  them,  by  pressure  and  the  abstraction 
of  heat,  can  be  reduced  to  the  liquid,  and  even  to  the  solid 
state ;  but  the  greater  part  of  them,  like  the  atmosphere,  resist 
every  attempt  at  solidification,  and  remain  permanently  gaseous 
at  all  temperatures.     They  also,  like  liquids,  diminish  the  weight 
of  all  solid  bodies  immersed  in  them,  by  the  weight  of  a  bulk 
of  the  gas  equal  to  that  of  the  body  immersed.     They  conse- 
quently possess  also  a  certain  buoyant  power,  and  all  bodies 
therefore  weigh  less  in  air  or  other  gases  than  they  do  in  a 
vacuum. 

9.  The  Atmosphere  a  Type  of  all  Gases.    Its  Properties. 
The  Atmosphere  possesses  the  properties  of  the  Gases  in  the 
most  marked  manner.    It  is  perfectly  clear  and  transparent.    It 
is  very  compressible,  and  by  pressure  may  be  made  to  occupy 
much  less  space  than  it  ordinarily  does.     It  is  highly  elastic,  and 
tends,  when  compressed,  to  return  to  its  original  volume.     The 

'space  which  it  occupies,  depends  upon  the  pressure  to  which  it 
is  subjected :  if  the  pressure  be  doubled,  its  volume  is  dimin- 
ished one-half ;  if  the  pressure  be  diminished  one-half,  the  space 

7.  What  is  the  type  of  all  Liquids?— 8.  State  the  peculiar  properties  of  Cases. 
Show  how  pressure  is  propagated  through  them. — 9  State  the  principal  properties  of 
the  Ak.  What  Ls  the  effect  of  pressure  upon  the  space  which  it  occupies  ? 


6  PROPERTIES  OF  THE  ATMOSPHERE. 

occupied  is  doubled.  The  atmosphere  possesses  weight,  and 
presses  with  an  average  force  of  about  fifteen  pounds  upon 
every  square  inch  of  the  earth's  suriace.  This  pressure  is  the 
weight  of  a  column  of  air  resting  upon  a  base  whose  area  is  one 
square  inch,  and  extending  from  the  lowest  to  the  highest  limit 
of  the  Atmosphere.  By  the  pressure  of  one  atmosphere  is 
always  meant,  a  pressure  of  fifteen  pounds  to  the  square  inch. 
The  weight  of  the  atmosphere  varies  continually,  and  this  va- 
riation is  measured  by  the  rise  and  fall  of  the  mercury  in  the 
tube  of  the  barometer.  When  the  air  is  heavier,  a  longer  column 
of  mercury  will  be  supported;  when  lighter,  a  shorter  column 
onbr  can  be  sustained.  When  the  pressure  is  exactly  equal  to 
fifteen  oounds,  it  will  sustain  a  column  of  mercury  thirty  inches 
higl  ,  the  weight  of  a  column  of  mercury  of  that  height,  and  with 
a  base  one  square  inch  in  area,  being  exactly  fifteen  pounds. 
One  hundred  cubic  inches  of  air,  at  30  inches  of  the  barometer, 
and  60°  Fahrenheit's  thermometer,  weigh  30.829  grains.  The 
body  of  a  man  of  medium  size,  exposes  a  surface  of  about  fif- 
teen square  feet,  and  he  must  consequently  sustain  a  pressure 
of  more  than  30,000  pounds,  or  about  fifteen  tons.  This  vast 
weight  is  carried  without  effort,  because,  in  consequence  of  the 
propagation  of  pressure  by  the  air,  equally  in  all  directions,  the 
external  pressure  is  counterbalanced  by  an  equal  pressure  ex- 
erted from  within,  through  the  medium  of  the  air  which  pene- 
trates into  the  interior  of  the  body.  As  there  is  the  same 
amount  of  pressure  upward,  as  there  is  downward,  the  air,  in 
fact,  exerts  a  certain  buoyant  power,  which  tends  to  support  his 
body  and  render  his  movements  even  more  free  and  easy  than 
they  would  be  in  a  vacuum.  As  we  ascend  in  the  atmosphere, 
its  weight  and  pressure  diminish;  and  at  2.7  miles  its  pressure 
is  but  seven  and  a  half  pounds  to  the  square  inch,  and  the  ba- 
rometer stands  at  only  fifteen  inches.  The  height  of  the  mer- 
cury in  the  tube  of  the  barometer,  is  therefore  an  excellent 
measure  of  altitude.  On  the  contrary,  as  we  descend  below 
the  level  of  the  sea,  the  atmospheric  pressure  increases,  and  the 
mercury  in  the  tube  of  the  barometer  has  been  known  to  rise  to 
forty-five  inches.  The  extreme  range  of  the  barometer  between 
the  highest  altitudes  reached  in  balloons,  and  the  greatest  depth 
.  beneath  the  level  of  the  sea,  is  from  thirty-three  to  thirty- 

9.  What  is  the  pressure  of  the  Atmosphere  to  the  square  inch  ?  By  what  instru- 
ment is  the  atmospheric  pressure  measured  ?  What  is  the  amount  of  this  pressure  upon 
the  bo-lv  of  a  man  ?  What  change  takes  place  in  the  atmospheric  pressure  as  we  ascend 
into  the  air  ?  What  is  the  ran»e  of  the  barometer  ?  What  is  the  variation  of  pressure 
upon  the  body  of  a  man  within  these  limits  ? 


PROVINCE    OF    NATURAL    PHILOSOPHY.  7 

four  inches;  and  as  the  variation  of  one  inch  produces  a  change 
of  pressure  upon  the  body  of  a  man,  of  1,000  pounds,  the  vari- 
ation of  pressure  experienced  in  these  cases  amounts  to  thirty- 
three  or  thirty-four  thousand  pounds.  The  distance  to  which 
the  atmosphere  extends  above  the  earth  cannot  be  very  accu- 
rately determined,  but  is  estimated  at  about  forty-five  miles. 

10.  The  General  Properties  of  Matter,  as  Solid,  L'quid  and 
Gaseous,  ars  treated  of  by  Natural  Philosophy.     These  gen- 
eral properties  are  essential  to  Matter,  and  must  be  taken  into 
view  in  forming  a  correct  idea  of  it.     They  constitute  the  sub- 
ject of  Natural  Philosophy,  and  it  is  to  that  science  that  we 
mast  resort  for  a  detailed  and  systematic  description  of  the  gen- 
eral properties  of  the  matter  of  the  universe,  as  it  exists  in  the 
three  different  states,  solid,  liquid,  and  gaseous.     But  partic- 
ular kinds  of  matter,  forming  the  various  special  substances  that 
surround  u-;,  possess  additional  properties  which  it  is  the  pecul- 
iar province  of  chemistry  to  investigate.     The  general  proper- 
ties of  matter  must,  however,  first  be  understood;  and  therefore 
an  acquaintance  with  the  first  principles  of  natural  philosophy 
is  a  necessary  preliminary  to  the  study  of  chemistry ;  while,  on 
the  other  hand,  a  knowledge   of  chemistry  is  a  necessary  sup- 
plement to  natural  philosophy,  if  it  be  wished  to  have  a  com- 
plete understanding  of  the  true  nature  of  the  various  forms  of 
matter  which  surround  us. 

11.  Chemistry  treats  of  the  same  Properties  of  Matter  as 
Natural  Philosophy,  and  of  others  bo  >ido.     The  properties  of 
Matter  treated  of  by  natural  philosophy  are  very  different  from 
those  investigated   by  chemistry.     Natural  philosophy  makes 
no  other  distinction  in  bodies  than  that  of  solids,  liquids,  and 
gases.     In  her  view  all  solids  are  alike,  all  liquids,  and  all  gases, 
because  they  all  possess  the  same  general  properties.     Chem- 
istry, on  the  other  hand,  treats  of  every  particular  solid,  liquid, 
and  gas,  and  shows  in  what  respects  each  differs  from  every 
other.     Natural  philosophy  takes  notice  only  of  the  external  and 
obvious  properties  of  bodies,  such  as  Color,  Weight,  Density, 
Elasticity,  and  those  which  belong  to  all  matter  in  the  mass, 
whether  solid,   liquid,   or  gaseous.      Chemistry,  on  the   other 
hand,  deals  with  the  internal  constitution  of  Matter,  seeks  to 
take  it  to  pieces,  to  resolve  it  into  its  elements,  to  ascertain  of 

9.  What  is  the  height  of  the  Atmosphere  ?— 10  What  science  takes  note  of  the 
general  properties  of  solids,  liquids,  and  gases  ?  What  science  treats  of  special  kinds 
of  Matter? — 11.  What  is  the  difference  between  natural  philosophy  and  chemistry? 
Why  is  chemistry  a  science  of  analysis  ? 


8  PROVINCE    OF    CHEMISTRY. 

what  simple  substances  every  variety  of  it  consists,  and  to  study 
the  properties  and  relations  of  each.  It  is  essentially  a  science 
of  analysis,  and  its  great  object  is  to  find  out  what  all  sub- 
stances are  made  of,  and  what  action  they  exert  on  each  other 
when  brought  into  contact;  to  study  the  nature  of  the  compounds 
which  they  form,  and  to  ascertain  the  character  of  the  force 
which  produces  their  union. 

12.  The  Study  of  Matter  forms  the  Subject  of  other  Sci- 
ences besides  Natural  Philosophy  and  Chemistry,  viz.,  Min- 
eralogy, Botany,  and  Zoology.     If  we  regard  material  objects 
in  reference  to  their  external  form,  the  different  arrangement  of 
their  parts,  their  power  of  growth,  of  motion,  and  of  reproducing 
other  objects  like  themselves,  in  short,  if  we  regard  Matter  as 
entering  into  the  structure  of  minerals,  plants,  and  animals,  and 
classify  these  according  to  the  degree  of  resemblance  found  in 
their  internal  and  external  organization,  we  are  led  to  the  three 
descriptive  sciences  which  constitute  Natural  History,  viz.,  Min- 
eralogy, or  the  description  and  history  of  minerals,  Botany,  or 
the  description  and  history  of  plants,  and  Zoology,  or  the  de- 
scription and  history  of  animals.     If,  on  the  other  hand,  we 
regard  material  objects  entirely  apart  from  their  form  and  or- 
ganization, and  only  as  composed  of  matter  in  general,  we  are 
confined  to  the  sciences  of  natural  philosophy  and  chemistry. 

13.  Difference  between  Natural  Philosophy  and  Chemistry 
illustrated  by  an  Example.     Take  a  piece  of  marble,  for  in- 
stance :  it  possesses  weight,  and  is  influenced  by  the  force  of 
gravity;  it  has  color,  density,  opacity;  it  is  composed  of  small 
particles  bound   together  by  the  force  of  cohesion,  and  the,-e 
particles,  however  minute,  are  yet,  each  of  them,  as  truly  marble 
as  any  portion  of  the  mass,  however  large.     These  are  the  only 
properties  of  the  marble  which  are  noticed  by  natural  philos- 
ophy ;  but  there  are  others,  besides.     Each  little  particle  of  the 
marble,  however  small,  is  a  compound  substance,  made  up  of 
three  elements,  very  different  from  marble,  and  very  different 
from  each  other  in  all  their  properties,  viz. :  a  metal  named  Cal- 
cium, common  charcoal  or  Carbon,  and  a  gas  named  Oxygen. 
These  three  substances,  when   brought   into  close  proximity, 
exert  a  certain  action  upon  each  other :  they  are  drawn  toward 

12.  What  other  sciences  does  the  study  of  matter  include  ?  What  is  Mineralogy  ? 
What  is  Botany?  What  is  Zoology  ?— 13.  Illustrate  the  difference  between  natural 
philosophy  and  chemistry  by  a  piece  of  marble.  What  force  unites  the  particles  of  mar- 
ble of  which  a  mass  of  marble  consists  ?  To  what  science  does  the  consideration  cf  the 
force  of  cohesion  belong  ?  '  What  are  the  three  substances  of  which  each  particle  of 
marble  is  composed  ? 


CHEMICAL    EXPERIMENTS. 


9 


each  other,  and  tend  to  unite  to  form  a  fourth  substance  entirely 
distinct  in  all  its  properties  from  those  of  the  elements  that  enter 
into  it.  There  are  more  than  sixty  such  elementary  substances, 
all  of  which  tend  to  act  upon  each  other,  and  to  unite  so  as  to  form 
new  substances,  whenever  they  are  brought  into  contact.  It  is 
the  properties  possessed  by  these  elements,  and  by  the  compound  .j 
which  they  form,  the  force  which  unites  them  together,  and  the 
character  of  the  action  which  they  exert  upon  each  other,  that 
constitute  the  subjects  of  which  chemistry  takes  cognizance. 

14.  Chemistry  is  a  Science  of  Experiment.    With  many  va- 
rieties of  Chemical  Action  we  are  familiar.     Sugar  dissolves  in 
water  ;  bright  iron  rusts  in  the  air,  and  when  heated  in  the  fire, 
becomes  covered  with  black  scales;  wood  and  coal  burn,  and  are 
converted  into  invisible  gases  ;  illuminating  gas  gives  forth  light 
and  heat,  and  then  disappears  ;  soda  powders,  when  mingled  in 
water,  produce  a  large  quantity  of  gas,  which  escapes  in  foam  ; 
charcoal,  when  inflamed,  gives  forth  an  invisible  gas  which  puts 
out  lighted  candles,  and  destroys  life.     With  these,  and  many 
other  instances  of  the  action  of  different  kinds  of  matter  on  each 
other,  we  are  already  familiar,  for  they  fall  under  our  notice 
every  day  ;  but  it  is  chemistry  which  investigates  and  explains 
them.     Where  this  explanation  is  not  easy,  experiments  are 
invented  for  the  purpose  of  ascertaining  the  truth.     Chemistry, 
consequently,  is  a  science  of  experiment. 

15.  A  Chemical  Experiment:  what 
it  is.     A   Chemical    Experiment  is    a 
process  devised  for  the  purpose  of  elicit- 
ing or  illustrating  some  important  chem- 
ical truth.     Suppose  we  wish  to  ascer- 
tain of  what  common  Salt  is  made  :  we 
pour  some  common  sulphuric  acid  or  oil 
of  vitriol,  which  may  be  procured  at 
any  druggist's,  upon  a  little  table  salt  in 
a  glass  llask  provided  with  a  cork  and 
a  piece  of  bent  tube  like  that  in  Ftg.  1. 
Sulphuric  acid  is  a  compound  of  sulphur 
and  oxygen  gas,  and  is  a  thick  and  oily 
liquid.     As  soon  as  it  touches  the  salt, 
an    effervescence    is    produced,    and  a 

white,  pungent  vapor  formed,  which  es-     A  comical  E'.perim*»t. 


13.  How  many  elementary  substances  are  there?  Mention  the  subjects  of  which 
chemistry  takes  cognizance.  —  11.  Mention  some  instances  of  chemical  action.  —  15.  If 
we  wish  to  know  of  what  common  sa.Ltii  conaposuJ.  what  do  we  do  ?  What  ig  sulpliuri* 


10  USES    OF    CHEMISTRt. 

capes  into  the  air.  If  now  the  end  of  the  tube  discharging  the 
vapor  be  dipped  into  a  wine-glass  partly  filled  with  absolution 
of  purple  cabbage,  the  purple  color  is  immediately  turned  to 
red ;  if  dipped  into  water,  the  water  becomes  acid.  We  con- 
clude, therefore,  that  common  salt  contains  a  substance,  which, 
when  driven  out  by  sulphuric  acid,  has  a  most  pungent  and 
irritating  odor,  an  acid  taste,  and  the  property  of  turning  veg- 
etable blue  colors  red.  We  say,  therefore,  that  salt,  when 
treated  in  this  way,  gives  forth  an  acid.  This  is  what  is  called 
a  Chemical  Experiment;  and  the  science  which  devises  pro- 
cesses like  this,  and  traces  their  results,  is  called  the  science  of 
chemistry. 

16.  Chemistry  is  connected  with  many  Curious  Processes 
in  the  Arts.     If  into  the  flask  used  in  the  experiment  just  de- 
scribed, still  containing   oil  of  vitriol  and  salt,  we  put  a  little 
Oxide  of  manganese,  and  apply  heat,  the  white  vapor  disap- 
pears, and  is  replaced  by  a  gas  of  a  green  color ;  and  what  is 
very  singular,  if  this  green  gas  be  made  to  pass  into  a  wine-glass 
containing  a  solution  of  purple  cabbage,  or  some  of  the  liquid 
turned  red  in  our  last  experiment,  these  liquids  almost  at  once 
become  colorless,  and   we  observe,  as  the  bubbles  of  gas  es- 
cape, that  they  diffuse  a  very  disagreeable  odor.     Here  we  have 
another  experiment  illustrative  of  a  Chemical  process  of  a  very 
curious  and  important  character,  one  which  is  daily  performed 
upon  an  immense  scale,  in  the  arts,  for  the  purpose  of  bleaching 
the  cotton  and  linen  fabrics  which  we  wear,  and  of  making  th« 
rags  from  which  writing  and  printing  pnpers  are  manufactured, 
fair  and  white.     The  green  gas  in  this  experiment  is  called 
Chlorine,  and  it  is  contained  in  common  salt,  united  with  a 
bright  and  shining  metal  named  Sodium.     Common  salt  is  com- 
posed exclusively  of  these  two  elements,  and  takes  from  them 
its  chemical  name,  Chloride  of  Sodium. 

17.  Chemistry  explains  the  nature  of  Medicines.  If,  again, 
into  this  green  Chlorine  gas,  we  dip  a  little  hot  Mercury,  the 
metal  immediately  begins  to  burn,  and  to  emit  a  white  cloud, 
producing  a  substance  known  in  medicine  as  Corrosive  Subli- 
mate, a  virulent  poison  composed  of  chlorine  and  metallic  mer- 
cury.    The  medicine  Calomel  is  also  composed  of  chlorine  arid 

15.  What  takes  place  when  sulphuric  acid  is  poured  on  the  salt  ?  What  effect  has 
the  substance  driven  out  of  the  salt,  on  vegetable  blues  ? — Ifi.  What  process  in  the 
Arts  is  explained  by  chemistry  ?  What  is  the  green  pas  named  that  is  driven  out  of  the 
Halt  ?  What  other  substance  besides  chlorine  is  contained  in  salt  ? — 17.  What  is  the 
effect  of  putting  hot  mercury  into  chlorine?  What  is  the  difference  between  corrosive 
gublimate  and  calomel  ? 


USES    OF    CHEMISTRY.  11 

mercury,  but  it  has  double  the  quantity  of  mercury  in  it  that 
corrosive  sublimate  has.  Calomel  may  therefore  be  made  by 
adding  an  additional  quantity  of  mercury  to  corrosive  sublimate. 
Here  we  have  another  chemical  process  of  great  importance  in 
the  preparation  and  administration  of  medicines. 

18.  Chemistry  explains  the  change  which  Respiration  pro- 
duces in  the  Air.     IF,  through  a  piece  of  glass  tube,  we  breathe 
air  from  the  mouth  into  a  tall  wine-glass  containing  lime-water, 
the  water  will  immediately  acquire  a  white  color  and  become 
turbid ;  and  if,  after  breathing  some  minutes,  we  gently  lower 
a  lighted  taper  almost  to  the  surface  of  the  water,  it  will  be  at 
once  extinguished.     A  small  insect,  introduced   in   the   same 
manner,  will  soon  die.     From  this  experiment  it  is  evident  that 
there  issues  from  our  mouths  in  breathing,  an  invisible  substance 
which  has  the  power  of  turning  lime-water  white,  extinguishing 
lights,  and  destroying  animal  life ;  and  this  explains  why  it  is, 
that  if  a  number  of  persons  are  confined  in  a  small  closed  room, 
unprovided  with  means  for  ventilation,  they  are  soon  suffocated. 
This  invisible  gas  is  called  Carbonic  Acid,  and  is  a  compound 
of  Charcoal  and  Oxygen.     It  is  produced  by  the  burning  of 
charcoal,  and  gas,  and  oil,  as  well  as  by  the  breathing  of  animals, 
and  this  accounts  for  the  "fact  that  death  is  so  often  caused  by 
the  burning  of  these  sub-tances  in  closed  apartments,  and  shows 
the  necessity  of  free  ventilation.     Here  we  have  a  great  danger, 
the  real  nature  of  which  is  made  known  to  us,  as  well  as  the 
importance  of  guarding  against  it,  by  the  science  of  which  we 
propose  to  treat. 

19.  Chemistry  is  connected  with  Agriculture.    The  farmer, 
as  is  well  known,  if  he  wishes  to  increase  the  amount  of  his 
crops,  plentifully  manures  his  fields.     Chemistry  teaches  us  that 
one  of  the  most  important  constituents  of  all  animal  manures  is 
the  gas  Ammonia,  and  shows  how  its  escape  into  the  air,  be- 
fore the  manure  is  worked  into  the  soil,  can  be  prevented.     It 
teaches  us  that  ammonia  is  itself  composed  of  two  other  distinct 
gnses,  Nitrogen  and  Hydrogen,  in  the  proportion  of  one  atom  of 
the  former  to  three  of  the  latter,  and  that  it  is  the  substance 
which  gives  to  commoa  hartshorn  its  pungent  odor  and  other 

IT.  Of  what  use  is  chemistry  in  the  manufacture  of  medicines  ? — 18.  What  takes 
place  when  breath  is  forced  from  the  lungs  through  lime-water?  What  happens  to  ;\ 
lighted  taper  introduced  into  the  wine-glass  ?  To  an  insect?  What  change  Is  produced 
in  the  air  by  respiration?  By  the  burning  of  gas  and  oil?  Why  is  ventilation  neces- 
sary?— 19  Wlv.t  ?al nable  substance  does  chemistry  disclose  in  manure?  What  is  am- 
paonia  ?  What  has  it  to  do  with  guano  ? 


12  USES    OF    CHEMISTRY. 

characteristic  properties.  Chemistry  shows  us  how  we  can  ap- 
ply it  to  plants  in  other  forms  than  that  of  barn-yard  manure, 
especially  in  the  state  of  guano,  points  out  the  special  manures 
that  different  plants  require,  and  teaches  us  how  to  manufacture 
them.  It  is  to  chemistry  that  we  arc  indebted  for  our  knowl- 
edge that  Phosphorus  is  valuable  as  a  fertilizer,  particularly  in 
the  culture  of  wheat  and  other  grains,  that  it  is  a  simple  sub- 
stance contained  in  bones,  and  that  bone-dust  and  the  phosphates 
of  Lime,  which  arc  made  from  bones,  are  of  great  value  for 
enriching  the  soil.  That  plants  require  ample  supplies  of  proper 
food  in  order  to  thrive,  and  that  without  it  they  must  languish 
and  die,  is  another  truth  of  the  greatest  importance,  for  which 
we  arc  chiefly  indebted  to  this  science. 

20.  Chemistry  treat*  of  the  Extraction  of  Metals  from  their 
Ores.     It  is  Chemistry  that  shows  us  how  to  extract  iron  and 
other  metals  from  the  stony  ores  in  which  they  are  found  in  the 
earth,  and  explains  how,  by  heating  these,  after  they  have  been 
ground  and  mixed  with  charcoal  and  lime,  the  pure  metals  are 
left  behind,  and  the  impurities  with  which  they  were  mingled  are 
scj>arated  from  them.     It  is  therefore  to  chemistry  that  we  are 
indebted  for  the  iron  employed  in  the  construction  of  railroads, 
steamboats,  and  every  kind  of  machinery,  as  well  as  for  the  other 
metals  which  arc  used  so  abundantly  in  the  various  arts.     It  is 
chemistry  also,  by  teaching  how  to  extract   phosphorus  from 
hones  thai  enables  us  to  manufacture  the  common  friction  match 
abundantly  and  cheaply. 

21.  Chemistry  is  connected  with  the  Manufacture  of  Gas, 
and  with  most  of  the  Useful  Arts.     The  printing  of  calico,  and 
nllproce-<e«.  for  dyeing  cloth,  the  preparation  of  illuminating  pis 
from  coal  and  oil,  the  making  of  soap  and   candles,  the  distilla- 
tion of  perfumery,  the  r:ii>ing  of  bread,  the.  manufacture  of  M>«!U 
water,  and  innumerable  arts  of  a  similar  kind,  all  depend   upon 
chemical  principles. 

22.  Chemistry  explains  the  Great  Natural  Processes  of 
Respiration  and  Combustion.     Finally,  it   is   Chemistry  that 
explains  why  atmospheric  air  is  essential  to  the  lite  of  animals 

I'.V  What  nutabuic*.  valuable  a*  a  fertilizer,  is  foun.l  in  bones  ?     What   pnvit  agricul- 
tuval  truth  is  taught  by  chemistry  ?—  20.  What  *n<>).  «  tn  n  <  t  n  <  t- 

o  Is  from  their  ore  *  ?  To  what  science  are  \ve  indebted  for  the  chc.-ip  and  abundant 
supply  of  iron  '  Of  phosphorus  and  friction  matolu  1  ^  .1  other  art* 

pendent  Upon  chemistry  tor  M»CI.  ntiou'— 22    What   light   .1. 

throw  upou  revpiration  and  combustion?  Han  it  am  thing  to  do  with  tin-  life  of  animaN 
and  plants,  or  with  the  lighting  of  fires,  the  generation  of  steam,  or  the  movement  <>f 
machinery  t 


HISTORY    OF    CHEMISTRY.  13 

and  plant?,  and  that  it  is  by  the  rapid  combination  of  the  Car- 
bon and  Hydrogen  of  wood  and  c  ):il  with  the  Oxygen  of  the 
air,  that  combustion  is  produced.  Thus  Chemistry  teaches  u> 
what  it  is  that  keeps  vegetable  and  animal  life  in  existence,  ami 
what  it  is  that  furnishes  the  heat  required  in  most  of  the  art-, 
in  cooking,  in  warming  houses,  in  generating  steam,  and  setting 
in  motion  steam  engines,  steamships,  and  all  the  rest  of  our 
varied  and  complicated  machinery. 

23:  The  Importance  of  Chemistry.  Thus  we  see  very  plainly 
how  important  a  knowledge  of  its  principles  must  be  to  every 
manufacturer  of  cotton  and  paper,  to  every  physician,  farmer, 
and  worker  in  metals;  to  all  makers  of  locomotives  and  steam 
engines  ;  to  all  manufacturers  of  gas,  and  indeed  to  all  persons, 
whatever  their  occupations,  since  it  enables  them  to  carry  on 
their  various  pursuits  successfully,  and  to  preserve  their  health, 
while,  at  the  same  time,  it  gives  them  an  intelligent  apprecia- 
tion of  the  great  operations  of  Nanire  which  are  continually 
going  on  around  them.  The  phenomena  of  combustion,  of  res- 
piration, of  artificial  illumination,  and  of  the  action  of  the  a:- 
mo>j)here  on  the  soil,  are  all  explained  by  it,  and  a  knowledge 
of  its  principles  should  be  possessed  by  every  intelligent  man. 

24.  Chemistry  furnishes  Striking-  Proofs  of  Design*.      ^  ' 
Science  furnishes  more  striking  instances  of  Design  in  CYeation, 
more  convincing  proofs  of  the  existence  of  (Jod,  or  more  sat- 
isfactory  illustrations  of  His    Power,   Wisdom,   and  (Joodness. 
It  teaches  more  forcibly  than  any  oilier  Science,  our  entire  de- 
pendence from  moment  to  moment,  for  life  and  breath,  upon  a 
Being  higher   than  ourselves,  and  that  it  is  not  in  man,  whose 
breath  is  in  his  nostrils,  to  direct  his  own  steps;   shows  how  im- 
po-sible  it  is  to  violate  any  even  of  the    Physical    Laws  of  the 
Almighty  with  impunity,  and  conduces  powerfully  therefore  to 
the  promotion  of  principles  of  Ilumilitv,  Devotion,  and   Obe- 
dience. 

25.  The  History  of  Chemistry.     The  History  of  Chemistry 
corn-indices  with  the  first  ettorts  of  man   to  appropriate  the  nat- 
ural world  to  his  use.  and  to  fabricate  out  of  rude  matter,  articles 
of  luxury  iwid  necessity.      A  practical  knowledge  of  the  chem- 
ical properties  of  common  substances  must  have  been  po-se-  rd 
from  the  earliest  ages,  by  all  persons  engaged   in  the  extraction 

23.  To  what  tri'les  :\n>l  professions  is  a  knowledge  of  its  principles  essential  '  \Vliv 
should  all  persons  desire  to  know  M>met  mi'/  of  tiiis  science.' — 24.  \Vii:it  lii:  it  does  it 
tliro\v  upon  the  relations  of  M.m  to  his  Creator.'  \VUat  does  it  show  iu  regard  to  the 
cUonicter  of  God  ?— 25.  Trace  the  History  of  Cucumtrv. 


14  USE    OF    THE    BALANCE. 

of  metals  from  their  ores,  and  in  the  manufacture  of  soaps,  dyes, 
and  glass.  The  art  of  making  leavened  bread  required  a  knowl- 
edge^ practical  chemistry.  The  lighting  of  a  common  fire  is 
one  of  the  most  beautiful  and  striking  of  all  chemical  processes ; 
and  the  earliest  chemist,  beyond  all  question,  was  the  man  who 
first  struck  a  spark  from  the  fiint,  in  order  to  produce  flame. 
Experience  daily  added  to  the  stock  of  chemical  knowledge. 
In  the  course  of  time  this  knowledge  was  greatly  increased  by 
the  invention  of  ingenious  experiments,  and  by  the  researches 
of  the  Alchemists.  These  singular  men  prolessed  the  art  of 
converting  the  baser  metals  into  gold :  this  they  believed  could 
be  effected  by  means  of  the  Philosopher's  Stone,  which  they 
described  as  being  a  red  powder  having  a  very  peculiar  smell. 
They  also  entertained  the  opinion  that  there  was  a  great  similar- 
ity between  the  mode  of  purifying  gold  and  curing,  disease, 
and  that  the  Philosopher's  Stone  was  also  an  Elixir  of  Life, 
by  the  use  of  which  the  existence  of  man  could  be  indefinitely 
prolonged.  But  it  was  not  until  about  the  year  1774  that  Chem- 
istry became  fairly  entitled  to  rank  among  the  Sciences,  when, 
in  the  hands  of  the  illustrious  Lavoisier,  the  Balance  was  called 
in,  for  the  purpose  of  applying  its  rigorous  test  to  the  results  of 
all  chemical  experiments.  Since  that  time  its  progress  has 
been  rapid  and  brilliant;  and  hardly  any  names  shine  more 
brightly  on  the  rolls  of  fame,  than  those  of  the  Philosophers 
who  have  devoted  themselves  to  this  Science.  Priestley,  Caven- 
dish, Watt,  Lavoisier,  Davy,  Faraday,  and  Liebig,  possess  a  rep- 
utation limited  to  no  age  or  country. 

26.  Weight  and  Proportion  of  Great  Importance.  Modern 
Chemistry  depends  upon  the  Use  of  the  Balance.  As  Chem- 
istry undertakes  to  teach  the  composition  of  matter,  it  not  only 
requires  that  the  different  substances  entering  into  a  compound 
should  be  pointed  out,  but  also  the  proportions  in  which  they 
combine.  This  demands  the  constant  use  of  the  Balance,  and 
renders  the  subject  of  weight  one  of  the  greatest  importance  to 
the  chemist.  Nearly  all  the  great  chemical  truths  have  been 
rigorously  examined  and  tested  by  this  instrument,  and  it  is 
therefore  of  as  much  importance  to  the  chemist  as  the  telescope 
is  to  the  Astronomer.  It  is  constructed  with  the  greatest  accu- 
racy, and  so  much  importance  is  attached  to  its  indications,  that 
the  general  division  of  substances  into  Ponderable  and  Impon- 

25.  Who  were  the  Alchemists  ? — 2".  How  is  the  subject  of  proportion  connected  with 
chemistry?    Why  is  the  Balance  necessary  ?    How  should  it  be  constructed? 


FUNDAMENTAL    PRINCIPLE    OF    CHEMISTRY.  lo 

derable  is  founded  upon  them,  the  former  class  embracing  ev- 
erything that  has,  the  latter,  everything  that  has  not  any  appre- 
ciable weight. 

27.  Other  Apparatus  required  in  the  Study  of  Chemistry. 
Besides  the  balance,  the  most  important  apparatus  required  in 
chemistry  is  an  air  pump,  an  electrical  machine,  a  powerful 
gas  lamp,  alcohol  lamps,  a  platinum  crucible,  a  small  galvanic 
battery,  a  pneumatic  cistern,  bell  glasses  for  the  collection  of 
gases,  graduated  jars  for  their  measurement,  precipitate  glasses, 
flasks,  retorts,  glass  tubes  of  various  sizes,  India  rubber  bags 
and  tubing,  all  of  which  may  be  obtained  at  no  great  expense ; 
and  there  is  no  one  who  may  not  very  easily  attain  such  a 
knowledge  of  the  science  as  to  be  able  to  add  something  to  the 
stock  of  chemical  knowledge. 

23.  The  Fundamental  Principle  of  Chemistry  is  the  Inde- 
structibility of  Matter.  The  most  striking  of  all  Chemical 
phenomena  is  the  indestructibility  of  Matter,  a  truth  verified 
only  by  the  constant  use  of  the  balance.  Whatever  changes 
may  be  made  in  the  appearance  and  form  of  matter  by  any 
chemical  process,  none  of  it  is  destroyed.  The  sum  of  all  the 
results  of  every  chemical  process  weighs  exactly  the  same  as 
the  sum  total  of  the  weight  of  all  the  matter  that  entered  into 
the  process.  This  is  true  of  the  combustion  of  wood  and  coal 
in  air.  If  the  coal  be  weighed  on  the  one  hand,  and  on  the 
other,  the  air  which  surrounds  it,  and  which  serves  to  produce 
the  combustion,  it  can  be  proved  with  perfect  exactness  that 
the  sum  of  the  ashes  left,  and  of  the  water  and  gas  that  are 
formed,  is  equal  in  weight  to  the  sum  of  the  weights  of  the 
coal  and  of  the  air  which  has  been  consumed.  When  mer- 
cury is  heated  in  a  vessel  of  confined  air,  it  is  eventually  con- 
verted into  a  mass  of  red  scales,  by  uniting  with  one  of  the 
elements  contained  in  the  air,  and  the  volume  of  the  air 
within  the  vessel  is  at  the  same  time  considerably  diminished. 
If  the  red  scales  be  now  weighed,  they  will  be  found  exactly 
equal  in  weight  to  the  sum  of  the  weights  of  the  mercury  and 
of  the  air,  which  have  disappeared ;  in  other  words,  the  weight 
of  the  compound  produced  is  exactly  equal  to  the  weight  of  the 
elements  which  have  combined  in  order  to  form  it.  All  chem- 
ical processes  may  therefore  be  expressed  in  the  form  of  an 

26  Whit  is  the  difference  between  Ponderable  and  Imponderable  substances  ?  27. 
What  other  apparatus  is  required  besides  the  balance?  ]s  it  within  the  power  of  all 
persons  to  acquire  a  knowledge  of  this  science? — 28.  What  ia  the  fundamental  princi- 
ple of  chemistry  ? 


16  SIMPLE    AND    COMPOUND    SUBSTANCES. 

equation.  On  one  side  should  be  placed  all  the  substances  that 
enter  into  the  process ;  on  the  other,  all  the  results,  solid,  liquid, 
and  gaseous;  in  every  case,  these  are  exactly  equal  to  each  other. 
The  principle  laid  down  by  Lavoisier,  and  established  by  the  use 
of  the  balance,  is,  THAT  IN  NATURE  NOTHING  is  LOST,  AND' 
NOTHING  CREATED.  Substances  may  be  combined,  or  sepa- 
rated from  each  other;  but  whether  combined  or  separated, 
they  exactly  preserve  their  weight.  The  end,  therefore,  which 
chemistry  seeks  to  attain,  is  the  thorough  study  of  all  the  pon- 
derable matter  of  which  the  earth  consists,  whether  organic  or 
inorganic,  animal  or  vegetable,  mineral  or  metallic,  liquid  or 
gaseous.  Since  Lavoisier  conceived  the  happy  idea  of  introdu- 
cing the  balance  into  the  study  of  chemical  phenomena,  this 
science  has  advanced  with  steady  progress,  determining  the 
composition  and  ascertaining  the  mutual  relations  of  all  the  dif- 
ferent kinds  of  matter,  showing  that  they  are  composed  of  a 
comparatively  small  number  of  elementary  or  simple  substances, 
united  in  regular  proportions,  and  proving  that  the  great  chem- 
ical processes  unceasingly  going  on  in  Nature,  result  from  the 
action  of  these  simple  and  compound  substances  upon  each  other. 

29.  Simple  and  Compound  Substances,  what  they  are.     A 
compound  substance  is  one  which  can  be  taken  to  pieces  and 
separated  into  two  or  more  distinct  substances  having  different 
properties :  thus,  Water  is  a  compound  substance,  and  may  be 
separated  into  two  gases,  Hydrogen  and  Oxygen,  one  of  which, 
Hydrogen,  is  inflammable,  and  much   lighter   than   the   air; 
the  other,  Oxygen,  not  itself  inflammable,  makes  combustible 
bodies  burn  with  great  fury  and  brilliancy,  and  is  heavier  than 
the  air.     Neither  Oxygen  nor  Hydrogen,  however,  can  be  sep- 
arated into  other  substances,  nor  can  any  other  substance  be 
extracted  from  them;  consequently  they  are  called  Simple  sub- 
stances, or  Elements. 

30.  The  Meaning-  of  the  Word,   Element.      When  it  is 
said  that  a  chemical  substance  is  an  Element,  it  is  only  meant 
that  so  far  as  we  at  present  know,  it  is  incapable  of  decompo- 
sition.    Future  researches  may  show  that  many  of  those  now 
regarded  as  simple  substances  are  really  compound,  and  that 

28  How  may  all  chemical  processes  be  expressed  in  the  form  of  an  Algebraic  Equa- 
tion ?  What  great  principle  was  laid  down  by  Lavoisier?  What  has  been  discovered  in 
reirard  to  the  simple  and  compound  substances  of  which  matter  is  composed  ?— 29. 
What  is  a  compound  substance ?  What  is  a  simple  substance?  Illustrate  this  differ- 
ence in  the  case  of  water.  Is  oxypren  simple  or  compound?  Why  is  it  called  a  simple 
substance  ?— 30.  What  is  an  element?  Are  we  absolutely  sure  that  any  substance  is  an 
element  ? 


THE    ELEMENTS.  17 

some  of  those  now  considered  compound  are  really  simple. 
Chlorine  was  for  a  long  time  considered  a  compound  of  Oxygen 
and  Muriatic  acid ;  but  Davy  showed  that  it  is  truly  a  simple 
substance.  Potash,  on  the  other  hand,  was  universally  regarded 
as  a  simple  substance,  until  the  same  philosopher  proved  that  it 
was  composed  of  the  metal  Potassium,  and  Oxygen. 

31.  The  Number  of  the  Elements.     The  number  of  the  El- 
ements is  not  as  great  as  might  be  supposed.     Chemists  have  as 
yet  discovered  only  sixty-five.     Of  these,  fifteen  are  called  met- 
alloids, the  remainder  are  metals.      The  metalloids  are  very 
extensively  diffused,  but  the  greater  part  of  the  metals  are  quite 
rare ;  not  more  than  one-third  are  used  in  the  arts,  and  some  of 
them  are  found  in  such  small  quantities  as  to  have  been  detected 
only  by  the  most  refined  analysis.     The  list  of  the  elements  13 
steadily  increasing ;  four  new  metals,  Caesium,  Rubidium,  Thalli- 
um, and  Indium,  have  been  discovered  within  the  last  four  years. 

32.  Th3  Constitution  of  some  of  the  most  Important  Chem- 
ical Compounds.     By  the  steady  prosecution  of  chemical  re- 
search, the  composition  of  nearly  all  the  different  forms  of  mat- 
ter upon  the  earth  has  been  determined.     The  metals  are  all 
simple  substances,  and  therefore  incapable  of  decomposition ;  so 
also  are  sulphur,  carbon,  phosphorus,  iodine,  bromine,  and  the 
gases,  oxygen,  hydrogen,  nitrogen,  and  chlorine.     Water  is  com- 
posed of  eight  parts  by  weight  of  oxygen,  and  one  part  by 
weight  of  hydrogen ;  air,  of  four-fifths  by  volume,  nitrogen,  and 
one-fifth  oxygen ;  sulphuric  acid,  of  sulphur  and  oxygen ;  sul- 
phurous acid,  also,  of  sulphur  and  oxygen,  but  less  oxygen  than 
the  preceding;  nitric  acid,  of  nitrogen  and  oxygen;  nitrous  acid, 
of  nitrogen  and  oxygen,  but  less  oxygen  than  the  preceding; 
chloro-hydric  acid,  of  chlorine  and  hydrogen,  and  is  sometimes 
called  muriatic  acid ;  carbonic  acid,  of  carbon  and  oxygen,  and 
is  an  invisible  gas,  like  the  atmosphere ;  illuminating  gas  is  a 
compound  of  carbon  and  hydrogen;  ammonia,  of  nitrogen  and 
hydrogen.     Potash  is  an  oxide  of  pota-sium,  and  is  composed 
of  oxygen  and  the  metal  potassium;  soda  is  the  oxide  of  sodium, 
and  is  composed  of  the  metal  sodium  and  oxygen;  lime  is  the 
oxide  of  calcium,  and  is  composed  of  the  metal  calcium  and 

31  How  was  chlorine  formerly  regarded?  How  is  it  now  regarded?  How  is  potash 
reg-irJeJ  .' — 31  What  is  the  i  umber  of  the  elements  ?  How  many  of  them  are  non- 
metallic  ?  How  many  are  used  in  tlie  arts  ?  What  is  snid  in  regard  to  thoir  abundance  ? 
Il.ive  any  new  elements  been  recently  discovered?  What  are  they?  32.  AVhnt  is  the 
composition  of  water  ?  of  air  ?  sulphuric  acid?  carbonic  acid?  sulphurous  ncid  ?  nitric- 
acid  ?  nitrous  acid?  chloro-hydric  acid .'  muriatic  acid ?  carbonic  acid?  potash?  soda? 


16'  CHEMICAL    AFFINITY. 

oxygen.  The  compounds  of  oxygen  and  the  different  metals 
are  called  oxides:  thus,  there  is  the  oxide  of  mercury,  of 
iron,  of  lead,  of  tin ;  the  compounds  of  chlorine  and  the  metals 
are  called  chlorides,  as  the  chloride  of  sodium,  or  common  ?alt, 
the  chloride  of  mercury,  or  corrosive  sublimate,  the  chloride  of 
ammonia,  or  sal  ammoniac;  the  compounds  of  iodine  with  the 
metals  are  called  iodides,  as  the  iodide  of  mercury,  the  iodide 
of  potassium.  The  compounds  of  sulphuric  acid  with  the  differ- 
ent metallic  oxides  are  called  sulphates,  as  the  sulphate  of  iron, 
composed  of  sulphuric  acid  and  oxide  of  iron;  sulphate  of  lime, 
of  sulphuric  acid  and  lime,  or  the  oxide  of  calcium;  sulphate  of 
soda,  of  sulphuric  acid  and  soda,  or  the  oxide  of  sodium;  sul- 
phate of  potash,  of  sulphuric  acid  and  potash,  or  the  oxide  of 
potassium.  The  compounds  of  nitric  acid  and  the  metallic  ox- 
ides are  called  nitrates,  as  the  nitrate  of  lead,  composed  of  nitric 
acid  and  oxide  of  lead ;  nitrate  of  iron,  of  nitric  acid  and  oxide 
of  iron.  The  compounds  of  chloro-hydric  acid  and  the  me- 
tallic oxides  are  called  chloro-hydrates,  as  the  chloro-hydrate  of 
iron,  composed  of  chloro-hydric  acid  and  oxide  of  iion;  chloio- 
hydrate  of  lime,  of  chloro-hydric  acid  and  lime,  or  the  oxide  of 
calcium.  The  compounds  of  carbonic  acid  and  the  metallic  ox- 
ides are  called  carbonates,  as  carbonate  of  potash,  composed  of 
carbonic  acid  and  potash ;  carbonate  of  soda,  of  carbonic  acid 
and  soda;  carbonate  of  lime,  of  caibonic  acid  and  lime,  &c. 

33.  Chemical  Affinity,  or  the  Force  by  which  the  Elements 
are  united.  The  force  by  which  the  elements  are  united  into 
the  different  compounds  of  which  matter  chiefly  consists,  is  the 
force  of  Chemical  Attraction  or  Affinity.  There  is  no  element 
which  has  not  a  powerful  tendency  to  unite  writh  others,  and 
this  is  the  reason  why  simple  substances  are  so  seldom  found 
uncombined  in  Nature.  This  tendency  is  not  possessed  by  them 
all  in  an  equal  degree,  and  hence  some  are  found  in  a  free  state 
much  more  frequently  than  others.  This  force  of  Affinity  differs 
both  from  Cohesion  and  from  Gravity.  It  differs  from  gravity, 
in  that  it  acts  at  insensible  distances.  It  differs  from  cohesion, 
in  that  it  tends  to  unite  only  particles  of  different  kinds,  while 
cohesion  tends  to  unite  particles  of  the  same  kind.  Thus, 
a  piece  of  marble  is  a  collection  of  small  particles  attached  to 

32.  What  is  the  composition  of  oxide  of  mercury  ?  oxide  of  iron?  chloride  of  podium  ? 
sal  ammoniac?  chloride  of  mercury?  iodide  of  mercury  ?  sulphate  of  iron?  sulphate 
of  lime?  nitrate  of  lead?  nitrate  of  ammonia7  carbonate  of  potash?  carlnuite  of 
lime?— 33.  What  is  the  force  by  which  the  elements  a; e  united?  Describe  this  forre. 
HO-.T  does  it  differ  from  cohesion  ?  How  does  it  differ  from  gravity  ?  Illustrate  the  na- 
ture of  affinity  in  the  case  of  a  piece  of  marble. 


ACTIVE    AGENTS    OF    CHEMISTRY.  19 

each  other  by  cohesion?  these  are  called  integrant  particles, 
and  each  of  them,  however  minute,  is  as  perfect  marble  as  the 
mass  itself.  Each  of  these  integrant  particles,  however,  con- 
sists of  three  distinct  substances,  calcium,  carbon  and  oxygen, 
which  are  different  from  one  another,  as  well  as  from  marble, 
and  are  united  by  Affinity :  these  are  the  constituent  particles 
of  marble,  and  it  is  of  these  that  Affinity  has  the  exclusive  con- 
trol. The  study  of  this  force  is  essential  to  the  chemist,  and, 
indeed,  chemistry  may  be  defined,  the  science  whose  object  is, 
to  examine  the  relations  that  Affinity  establishes  between  bodies, 
ascertain  with  precision  the  nature  and  constitution  of  the  com- 
pounds it  produces,  and  determine  the  laws  by  which  its  action 
is  regulated. 

34.  Ths  Active  Agrents  of  Chemistry,  But,  while  Affinity 
is  the  force  by  which  the  Elements  are  united,  it  is  itself  con- 
trolled and  modified  by  the  three  great  agents,  Heat,  Light,  and 
Electricity.  Thus,  the  electricity  produced  by  a  small  galvanic 
battery  can  effect  the  decomposition  of  water,  a  firm  and  stable 
chemical  compound;  and  this  decomposing  action  of  the  battery 
is  not  limited  to  water,  but  extends  to  a  very  large  number  of 
compound  substances.  In  like  manner,  heat  will  decompose 
limestone,  or  the  carbonate  of  lime,  and  drive  off  the  carbonic 
acid;  it  will  also  decompose  chlorate  of  potash,  oxide  of  mer- 
cury, oxide  of  manganese,  nitrate  of  potash,  and,  in  fact,  the 
larger  part  of  all  chemical  compounds.  Light,  though  acting 
with  less  intensity  than  the  two  preceding  agents,  nevertheless 
produces  analogous  effects,  and  decomposes  many  compound 
substances.  This  is  shown  in  a  striking  manner  in  its  destruc- 
tion of  the  colors  of  various  bodies,  and  especially  in  the  power 
which  it  gives  to  the  leaves  of  plants  of  decomposing  carbonic 
acid.  On  the  other  hand,  these  agents  will  often  effect  the 
union  of  substances  which  under  ordinary  circumstances  refuse 
to  combine.  Thus,  oxygen  and  hydrogen  will  remain  uncom- 
bined  for  years,  though  mingled  in  the  same  vessel  in  proper 
combining  proportions;  but  if  the  smallest  particle  of  any  sub- 
stance in  active  inflammation  be  applied  to  the  mixture,  they 
will  unite  instantaneously  with  a  violent  detonation,  at  the  same 
time  forming  a  small  quantity  of  pure  water.  The  same  is  true 
of  carbon  and  oxygen,  which  will  remain  uncombined  for  ages, 
/  though  in  the  closest  proximity ;  but  if  the  smallest  particle  of 

34      By  what   is   Affinity  controlled?     What  are   the   Active   Agents  of  Chemistry? 
Give  some  instances  of  decomposition  produced  by  them  :  of  combination. 


20  THE    IMPONDERABLES. 

the  carbon  be  headed  red-hot,  combination  will  immediately  en- 
sue and  proceed  with  the  greatest  intensity.  In  like  manner, 
electricity,  if  made  to  pass  through  a  mixture  of  oxygen  and 
hydrogen,  will  cause  them  to  unite  with  a  violent  explosion ;  and 
if  a  succession  of  electric  sparks  be  transmitted  through  a  mix- 
ture of  oxygen  and  nitrogen,  we  shall  find  that  they  have  been 
made  to  combine  and  form  nitric  acid.  In  the  same  manner,  a 
beam  of  bright  sunlight,  allowed  to  fall  upon  a  mixture  of  equal 
volumes  of  chlorine  and  hydrogen,  will  cause  them  to  combine 
with  a  violent  explosion,  and  form  chloro-hydric  acid.  It  is  evi- 
dent, therefore,  that  the  force  of  Affinity  is  to  a  great  extent 
under  the  control  of  these  agents,  and  it  is  in  their  application 
for  the  purpose  of  modifying  this  force,  that  the  chemical 
arts  chiefly  consist.  Their  nature  ought  therefore  to  be  thjr- 
oughly  understood.  They  are  aLo  closely  connected,  in  some 
mysterious  manner,  with  the  constitution  of  matter,  so  that  this 
constitution  can  not  be  altered  without  their  manifestation.  They 
play  a  prominent  part  in  the  most  brilliant  phenomena  of  Ka- 
ture ;  they  meet  us  on  every  hand ;  they  are  everywhere  pres- 
ent, and  are  possessed,  therefore,  of  a  paramount  interest.  No 
chemical  process,  whether  performed  on  a  great  scale  in  Na- 
ture, or  on  a  small  scale  in  the  arts  or  in  the  laboratory,  can 
be  carried  on  without  the  development  or  the  action  of  the^e 
three  agents.  Thus,  in  the  experiments  already  described,  the 
rapidity  of  the  process  in  every  case  is  much  increased  by  the 
application  of  Heat.  In  some  of  them  great  Heat  is  produced; 
in  others,  currents  of  Electricity  are  set  in  motion ;  and  often- 
times the  result  of  both  is  the  production  of  vivid  Light. 

35.  The  Chemical  Agents,  Heat,  Light,  and  Electricity, 
are  commonly  called  Imponderables.  From  the  active  and 
energetic  nature  of  Heat,  Light,  and  Electricity,  they  are  called 
the  Chemical  Agents;  and  from  the  fact  that  they  JKSS^SS  no 
appreciable  weight,  so  that  a  body  is  no  heavier  for  their  accu- 
mulation, or  lighter  for  their  abstraction,  they  are  named  the 
Imponderables.  They  can  not  be  confined  or  exhibited  in  a 
mass,  like  ordinary  bodies ;  and  can  only  be  collected  through 
the  intervention  of  other  substances.  Their  title  to  be  consid- 
ered material  is  therefore  questionable,  and  the  effects  produced 
by  them  have  accordingly  been  attributed  by  some  to  certain 

34.  Why  should  these  agents  be  thoroughly  understood  ?  Is  it  possible  to  change 
the  constitution  of  any  substance,  without  meeting  with  them? — 3o  \V*hy  are  heat, 
light  and  electricity  called  Imponderables  ?  lias  their  title  to  be  called  material  ever  been 
questioned? 


THE    ORDER    OF    SUBJECTS.  21 

motions  or  affections  of  common  matter.  By  some  they  are  con- 
sidered as  only  modes  of  motion,  and  as  convertible  into  each 
other ;  and  this  view  is  beginning,  of  late,  to  attract  considera- 
ble attention.  It  must  be  admitted,  however,  that  they  appear 
to  be  controlled  by  the  same  powers  which  act  on  matter  in 
general,  and  that  some  of  the  laws  which  have  been  determined 
concerning  them  are  exactly  such  as  might  have  been  anticipa- 
ted on  the  supposition  of  their  materiality.  Hence  it  follows 
that  we  need  only  regard  them  as  subtile  species  of  matter,  in 
order  that  the  phenomena  to  which  they  give  rise  may  be  ex- 
plained in  the  language  and  according  to  the  principles  which 
are  applied  to  material  substances  in  general ;  and  as  such  they 
will  be  considered  in  what  immediately  follows,  the  thorough 
discussion  of  their  true  nature  being  reserved  until  we  have  be- 
come familiar  with  the  principal  facts  connected  with  them. 

35.  TJie  Study  of  Chemistry  should  beg-in  with  the  Chemi- 
cal Ag-ents.  As  Heat,  Light,  and  Electricity  exercise  a  control- 
ling influence  over  Affinity,  and  are  possessed  of  so  much  inter- 
est and  importance  in  the  explanation  of  chemical  phenomena, 
it  is  necessary  to  commence  the  study  of  this  science  with  an 
examination  of  their  principal  qualities.  We  can  then  pro- 
ceed to  the  study  of  the  composition  and  chemical  properties  of 
the  different  kinds  of  matter,  and  the  various  and  extraordinary 
changes  which  result  from  their  mutual  action. 

Chemistry  is  therefore  usually  divided  into  two  portions. 
The  nVst  treats  of  the  Chemical  Agents,  Heat,  Light,  and  Elec- 
tricity, anl  is  commonly  called  Chemical  Physics;  the  second, 
of  the  Chemical  properties  and  relations  of  the  various  kinds 
of  matter.  The  second  of  these  two  portions  is,  however,  itself 
also  divided  into  two  parts,  ihe  first  treating  of  the  chemical 
properties  of  the  Inorganic,  the  second  of  the  chemical  proper- 
ties of  Organic  matter.  The  general  arrangement  of  every 
complete  treatise  on  Chemistry  will  therefore  be  as  follows : — 

Part  I.  Chemical  Physics :  Heat,  Light  and  Electricity. 

Part  II.  Inorganic  Chemistry.     Part  III.  Organic  Chemistry. 

This  treatise  is  devoted  exclusively  to  the  1st  Part,  viz., 
Chemical  Physics:  Heat,  Light  and  Electricity. 

Inorganic  and  Organic  Chemistry  are  reserved  for  another 
volume. 

3").  What  other  view  is  taken  of  them  ?  Which  view  meets  with  the  most  favor  ? 
Way  is  it  convenient  to  regard  them  as  material  ?  What  view  is  taken  of  them  in  the 
present  work  ?  When  will  their  true  nature  be  considered  ? — 3;3.  With  what  should 
the atttdV of  chemistry  commence?  What  subject  immediately  succeeds  the  Chemical 
Agents?  Into  how  many  parts  is  chemistry  divided?  What  does  the  first  part  treit  o/? 
W  i  it  is  chemical  physics  ?  What  does  the  second  part  treat  of?  What  ia  the  general 
arrangement  ?  What  is  ths  subject  of  this  volume? 


22  THE  FIRST   CHEMICAL   AGOT; — HEAT, 

CHAPTER  II. 

THE  FIRST  CHEMICAL  AGENT  : HEAT. 

DIFFUSION  OF  HEAT  :  EXPANSION  :  LIQUEFACTION  :  EBULLITION  :  EVAP- 
ORATION :    SPECIFIC  HhAT  :    SOUKCtS   OF  HEAT  :   NATURE  OF  HEAT. 

§  1.  —  Diffusion  of  Heat. 

37.  The  Nature  of  Heat.  Heat  is  known  only  from  its  ef- 
fects. It  has  never  been  isolated,  or  completely  separated  from 
material  substances,  so  as  to  be  obtained  in  a  perfectly  pure 
and  uncombined  state,  and  consequently  its  true  nature  is  alto- 
gether Ji  subject  of  inference  and  hypothesis.  There  are  two 
theories  in  regard  to  the  nature  of  Heat,  which  serve  with  nearly 
equal  completeness  to  explain  a.l  the  phenomena  to  which  it 
gives  rise.  According  to  the  first,  Heat  is  material,  and  sub- 
ject to  all  the.  laws,  which  control  ordinary  matter.  It  is  re- 
garded as  an  extremely  subtile  fluid,  pervading  all  space,  enter- 
ing into  combination  with  bodies  in  different  proportions,  producing 
the  various  effects,  of  change  of  temperature,  expansion,  lique- 
faction and  vaporization.  The  second  theory  regards  it  as  the 
effect  of  undulation  or  vibration,  produced  either  in  the  constit- 
uent molecules  of  bodies  themselves,  or  in  a  subtile  fluid  which 
pervades  them.  Modern  science  seems  to  lean  at  the  present 
moment  decidedly  towards  the  latter  of  these  theories ;  but  as 
the  former  is  simpler  and  more  easily  understood,  and  greatly 
facilitates  the  demonstration  of  the  principal  properties  of  Heat, 
it  is  the  one  generally  preferred  for  the  explanation  of  the  effects 
which  are  produced  by  this  agent. 

33.  Heat  exists  in  two  states.  Heat  exi  ts  in  two  states  : 
first,  as  free  and  sensible ;  second,  as  combined  and  latent.  In  the 
first  state  it  gives  rise  to  what  is  called  the  sensation  of  heat, 
affects  the  thermometer,  and  produces  all  the  familiar  results 
invariably  ascribed  to  its  agency :  in  the  second,  it  enters  into 
combination  with  bodies,  and  tends  to  alter  their  condition,  pro- 
ducing the  liquefaction  of  solids,  and  converting  liquids  into 
va>ors;  when  such  a  change  in  the  state  of  matter  is  accom- 
plished, a  large  amount  of  heat  disappears,  ceases  to  exhibit  its 
usual  properties,  and  seems  to  be  buried  and  lost,  in  the  body 

37.  Why  is  the  nature  of  Heat  hypothetical  ?  State  the  first  theory  in  regard  to  it. 
State  the  second.  To  which  theory  does  Modern  Science  incline? — 38.  In  what  two 
states  does  Heat  exist  ? 


HEAT    PRESENT    IN    ALL    BODIES.  23 

in  question ;  in  this  second  state  it  is  called  heat  of  composition, 
or  Latent  Heat.  The  subject  of  the  combination  of  heat  with 
matter,  will  become  more  clear  as  we  proceed.  At  present  we 
shall  consider  only  the  properties,  which  Heat  possesses  in  its 
free  and  uncombined  s^tate. 

39.  Hsat  Preset  in  all  Bodies.  Heat  seems  to  be  present 
in  all  bodies,  and  there  is  no  process  by  which  it  can  be  wholly 
abstracted  fro  n  any  substance  :  for  however  cold  any  substance 
may  be,  if  it  be  carried  to  a  place  where  the  temperature  is 
still  lower,  it  will  again  give  out  heat,  and  continue  to  do  so  until 
its  temperature  has  become  the  same  with  that  of  the  surround- 
ing medium.  Thus  if  a  piece  of  ice  at  zero  of  Fahrenheit's 
thermometer,  were  transported  to  any  region  where  the  temper- 
ature was  60°  below  zero,  it  would  begin  to  emit  heat,  and  con- 
tinue to  do  so  until  its  temperature  had  become  reduced  to  that 
of  the  surrounding  air.  In  such  an  atmosphere,  the  ice  though 
at  0°  would  be  a  hot  body,  and  would  communicate  heat  to  all 
objects  in  its  vicinity.  Place  the  same  piece  of  ice,  thus  reduced 
to  a  temperature  60°  below  zero,  in  an  atmosphere  80°  below 
zero,  and  here  again,  compared  with  the  surrounding  medium, 
it  would  be  a  warm  body,  and  would  again  give  forth  heat,  until 
an  equilibrium  was  established  between  its  temperature  and 
that  of  the  objects  around  it.  As  this  process  might  be  carried 
on  without  limit,  it  is  quite  clear  that  heat  is  present  in  all 
bo  lies,  however  cold,  and  can  not  be  entirely  abstracted  from 
any  substance. 

43.  H3at  and  Cold  arc  Relative  Terms.  No  body  is  hot 
or  cold,  absolutely  of  itself,  but  only  so,  in  comparison  with  other 
bodies  near  or  in  contact  with  it.  So  far  as  our  sensations  are  con- 
cerned, heat  and  cold  depend  upon  circumstances.  The  same 
medium  will  feel  warm  at  one  time,  and  cold  at  another,  though 
possessing  the  same  temperature,  depending  upon  the  varying 
temperature  of  our  own  bodies.  Thus  the  air  of  a  cellar,  the 
temperature  of  which  is  very  nearly  the  same  both  in  winter  and 
summer,  will  feel  cool  when  we  enter  it  on  a  warm  summer's 
day,  but  warm  on  a  cold  day  in  winter.  A  traveler  descending 
from  the  summit  of  Mount  Etna,  will  find  his  garments  uncom- 
fortably warm,  when  half  way  down,  while  at  the  very  same 

State  what  is  meant  by  sensible  Heat,  by  heat  of  composition,  or  Latent  Rent. — 
Which  state  of  Heat  do  we  consider  at  present? — 39.  Show  that  Heat  is  present  Li  all 
bo'lie*,  however  cold. — 40.  Show  why  heat  and  cold  are  relative  terms  Explain  why  A 
medium  of  tlie  same  temperature  wHl  feel  hot  at  one  tiuio  and  cold  at  another.  Giy« 
the  illustration  of  a  traveler  ou  3Iouut  Etna. 


24  HEAT    THE    REPULSIVE    PRINCIPLE. 

place  another  traveler,  ascending  the  mountain  from  the  warm 
regions  below,  will  find  the  air  inconveniently  cool,  and  will 
wrap  his  garments  more  closely  about  him. 

The  White  Bear,  from  Greenland,  and  the  Elephant,  from 
Hindostan,  are  seen  to  suffer,  the  one  from  heat,  and  the  other 
from  cold,  in  the  atmosphere  of  the  same  menagerie.  Even  to 
the  same  person,  the  same  temperature  may  seem  both  hot  and 
cold  at  the  same  moment.  Thus  if  one  hand  be  placed  in  water 
at  40°  and  the  other  in 

water  at  150°,  and  then  T&  2- 

both  hands  be  plunged 
together  into  a  third 
vessel,  in  which  the 
water  is  at  90°,  one 

hand  will   experience  a  Sensations  of  Ueat  Relative. 

sensation  of  heat,  and 

the  other  of  cold,  though  the  temperature  to  which  both   are 

exposed,  is  the  same.     Fig.  2. 

41.  Heat,  the  Repulsive  Principle  of  Matter,  and  opposed 
to  Cohesion.     Heat  is  the  great  repulsive  principle  of  Nature, 
and  tends  to  separate  the  molecules,  and  consequently  increase 
the  dimensions  of  every  substance  into  which  it  is  introduced. 

It  is  opposed  to  cohesion  or  that  force  which  tends  to  draw 
the  particles  of  substances  together,  and  to  bind  them  closely  to 
each  other ;  and  it  is  upon  the  relative  strength  of  these  two 
forces,  that  the  condition  of  matter  as  solid,  liquid  and  gaseous, 
depends.  When  cohesion'  predominates  over  heat,  the  tody 
has  the  form  of  a  solid  ;  when  they  are  of  nearly  equal  Ftrrnglh, 
the  solid  is  converted  into  a  liquid ;  and  when  heat  predominates 
over  cohesion,  the  gaseous  state  results.  As  we  have  the  means 
of  increasing  and  diminishing  the  heat  of  a  body  within  a  very 
wide  range,  and  therefore  of  changing  at  will  the  strength  of 
the  repulsive  principle,  the  form  of  most  kinds  of  matter  may 
be  varied  at  pleasure  :  solids  can  be  converted  into  gases,  and 
ga^es  into  solids  :  snow  and  ice  changed  into  steam — an  invis- 
ible vapor ;  and,  on  the  other  hand,  carbonic  acid,  an  invisible 
gas,  condensed  into  a  white,  flaky  solid,  in  appearance  resem- 
bling snow. 

42.  Heat  tends  to  an  Equilibrium.     One  of  the  most  obvi- 
ous properties  of  heat  is  its  tendency  to  an  equilibrium,  that  is, 


Of  the  Polar  Bear  and  the  Elephant.  Give  the  illustration  of  the  two  hands  placed 
In  a  central  bowl  of  water  at  90°.  — 41.  Why  is  heat  called  the  repulsive  principle? 
To  what  force  is  it  opposed?  Show  how  the  state  of  bodies  as  solid,  liquid,  and  pas- 
eous  depends  upon  the  balance  between  heat  and  cohesion.— 41  What  is  the  obvious 
property  of  heat  ? 


IIZAT    SEEKS    AN    EQUILIBRIUM. 


25 


its  disposition  to  pa<s  from  a  hot  body  to  those  colder  than  itself. 
Tims  it'  several  bodies  of  ditferent  temperatures  be  placed  in  the 
same  room,  the  warmer  body  will  continue  to  impart  its  heat  to 
tho^e  which  are  colder,  until  they  all  indicate  the  same  tempe- 
rature by  the  thermometer.  This  tendency  to  an  equilibrium 
is  so  strong  that  it  is  impossible  to  maintain  the  temperature  of 
any  body  permanently  above  that  of  the  medium  in  which  it 
is  placed.  As  soon  as  heat  accumulates  in  any  body,  it  imme- 
diately begins  to  diffuse  itself  through  the  matter  which  sur- 
rounds it. 

43.  Three  Modes  in  which  Heat  seeks  an  Equilibrium. 
Heat  attains  this  equilibrium  in  three  ditierent  ways :  1st.  By 
Conduction.  This  takes  place  only  in  solids.  Thus  when  an 
iron  b.ir  is  heated  at  one  end,  the  heat  passes  from  particle  to 
particle  through  the  whole  bar,  until  every  part  has  reached  the 
san t3  temperature.  2d.  By  Convection.  This  takes  place  only 
in  the  liquids  and  ga>es.  In  these,  every  particle  is  in  turn 
brought  into  contact  with  the  portion  of  the  vessel  where  the 
heat  is  applied,  until  they  have  all  attained  the  same  temperature. 
3d.  By  Radiation.  In  this  case  the  heat  darts  through  an  ap- 
preciable space,  and  so  passes  from  a  hot  body  to  one  at  a  con- 
siderable distance.  By  this  process  a  hot  stove  sends  forth  rays 
of  heat  in  every  direction,  that  pass  through  the  air  without 
heating  it,  but  raise  the  temperature  of  all  bodies  upon  which 

Fig.  3. 


4    A    L 


Conduction   Grarfual. 


What:  is  the  effort  of  this  tendency  ?  -43.  What  are  the  modes  in   which  Ileat 
an  equilibrium  ?  Describe  them. 
2 


26 


CONDUCTION    OF    HEAT. 


they  strike.  In  like  manner  the  earth  is  warmed  by  rays 
which  emanate  from  the  sun,  and  have  passed  thiough  the  air 
without  raising  its  temperature. 

44.  First  Mode  in  which  Heat  is  Diffused.  —  Conduction. 
When  heat  is  conducted  through  bodies,  it  does  not  flush  through 
them  instantaneously,  like  electricity,  but  passes  successively  from 
particle  to  particle,  requiring  an  appreciable  time  for  the  pas- 
sao-e.  In  the  accompanying  figure  there  is  a  bar  of  iron,  having  a 
lamp  at  one  extremity.  Upon  the  upper  surface  are  arranged 
small  bits  of  Phosphorus,  at  equal  intervals;  on  the  lower  a 
number  of  marbles  have  been  attached  by  bits  of  wax.  The 
marbles  do  not  all  drop  at  the  same  time,  nor  do  the  bits 
of  Phosphorus  take  fire  at  the  same  instant,  but  successively ; 
and  this  shows  that  the  passage  of  the  heat  is  gradual.  Fig.  3. 
45  Bodies  Differ  in  Conducting  Power.  Heat  passes 
through  different  bodies  with  different  degrees  of  rapidity. 
gome  permit  it  to  pass  through  them  quite  rapidly ;  others  only 
very  slowly,  and  some  almost 
entirely  intercept  its  passage. 

Thus,  one    can   hardly   hold  a 

brass  pin  for  a  moment,  in  the 

flame  of  a  lamp,  without  burn- 
ing his  fingers,  while   a  piece  of 

glass  of  the  same  size,  may  have 

one  of  its  ends  melted,  without 

warming  the  other.     This   can 

be  proved  by  holding  a  bit  of 

iron   wire  by  one  hand  and  a 

piece  of  glass  rod  by  the  other, 

in  the  flame  of  a  .pint  Jamp. 


Difference  in  Conducting  Power. 


Different 


plainly  shown  by  the  apparatus,  rep- 
resented in  Fig.  5.  Rods  of  dif- 
ferent sub.tances  of  the  same  size 
and  leno-th,  are  covered  with  wax,  to 
the  distance  of  an  inch  from  their 
free  extremities,  tipped  with  little 
bits  of  phosphorus,  and  then  inserted 
into  pockets  upon  the  side  of  a  bra?s 
vessel,  filled  with  hot  water. 
~C*W?~*  phosphorus  is  inflamed,  and  the  wax 

>n   heat  pn^es  from  particle  to  particle.     Describe  Fig.  3. 
t  conducting  po,ver.-46.  Describe  1'ig-  5. 


RELATIVE    CONDUCTING   POWER    OF   METALS.  27 

commences  malting  upon  the  different  rods  at  different  intervals 
of  time ;  upon  the  best  conductor  first,  and  successively  upou 
the  others,  in  the  order  of  their  conducting  power. 

47.  Density  Favorable  to  Conduction.     Bodies  which  are 
most  dense  are  generally  the  best  conductors.     Thus  the  metals 
conduct  batter  than  stones  ;  stones  better  than  earth  ;  earth  bet- 
ter than  wood ;  and  wood  better  than  charcoal,  cloth  or  paper. 
But  sometimes  there  is  no  relation   between  the  density  of  the 
body,  and  its  power  to  conduct  heat.     Thus  platinum  is  the 
most  dense  of  the  metals,  but  it  is  not  by  any  means  the  best 
conductor  among  them,  and  glass  is  a  worse  conductor  than 
many  substances  of  much  less  density. 

48.  Relative  Conducting  Power  of  the  Metals.     The  fol- 
lowing table  presents   the   results  of  a  series  of  careful  experi- 
ments by  M.  Dcispretz,  in  regard  to  the  conducting  power  of 
the  metals  and  some  other  substances.     The  substances  em- 
ployed were  made   into  prisms  of  the  same  form  and  size.     At 
one  extremity  haat  was  applied  from  the  same   source,  and  its 
passage  along  the  prism  in  each  case  was  estimated  by  small 
thermometers,  placed  in  holes  drilled  at  regular  intervals,  and 
filled  with  mercury. 

Despretz'  Table  of  Conductivity  for  Heat. 


Gold,   . 

.    1000 

Tin,    . 

.     304 

Platinum,   . 

931 

Steel, 

218 

Silver, 

.     973 

Lead, 

.     179 

Copper, 

898 

Marble,    . 

24 

Brass, 

.     441 

Porcelain, 

.       12 

Iron, 

374 

Brick-clay, 

11 

Zinc,    . 

.     343 

49.  The  succeeding  table  of  the  conduction  of  heat  com- 
pared with  conduction  of  electricity,  was  prepared  by  MM. 
Wiedemann  and  Franz.  Their  apparatus  was  arranged  in  the 
sima  manner  as  that  of  M.  Despretz,  except  that  instead  of 
estimating  the  progress  of  the  heat  by  thermometers,  it  was 
done  by  a  small  thermo-electric  pile,  the  most  delicate  known 
instrument  for  measuring  heat,  to  be  described  hereafter.  The 
results  that  they  reached  were  very  different  from  tho;e  of  M. 

47  To  what  other  property  in  bodies  is  conduction  generally  proportioned. — 4S.  Des- 
cribe the  apparatus  of  DjspreU  for  determining  eondaction.  Give  liis  table  of 
conduction. 


28    CONDUCTION  FOR  HEAT  COMPARED  WITH  ELECTRICITY. 

Despretz,  and  showed  that  the  conducting  power  of  the  melals 
for  heat,  is  very  nearly  the  same  as  their  conducting  power  ior 
electricity,  and  that  the  conducting  power  of  Platinum,  notwith- 
standing its  great  density,  is  very  low. 

Table  of  Conductivity  for  Heat  compared  with  that  for  Electricity. 

Heat.  Electricity 

Silver,  ....     100  ....     IdO 

Copper,        .  .  .  74       .  .  .  .  78 

Gold,     .  .  .  .53  .  .  .  .59 

Brass,  .  .  .  24       .  .  .  .  22 

Tin,       .  .  .  .15  .  .  .  .23 

Iron,         2  ...  .  .  12       .  .  .  .  13 

Lead,    .  -v  '."        .        "'<;V       9  .  .  .  .11 

Platinum,    ...  8  -, —        .  10 

German  Silver,  .  .6  .  .  .  .6 

Bismuth,      .        _ ,.  ",.'  2       .         .'"•'/•         •  •  2 

50.  Porous  Bodies  Dad  Conductors.  Solid  substances  con- 
duct heat  in  all  directions,  whether  upward,  downward,  or  side- 
ways, with  nearly  equal  facility.  A  notable  exception  to  this 
is  seen  in  the  case  of  certain  crystals,  such  as  quartz,  which 
conduct  heat  with  greater  facility  in  the  direction  of  their  optic 
axis,  or  of  their  greatest  length,  than  at  right  angles  to  it. 
Wood  is  also  said  to  conduct  heat  with  greater  rapidity  in  some 
directions  than  in  others,  and  more  easily  with  the  grain  than 
across  it.  Of  all  solids,  those  which  are  most  porous  conduct 
heat  with  the  least  rapidity.  On  this  account  flannel  is  warmer 
in  winter  than  silk  or  linen.  It  is  owing  to  the  air,  which 
loose,  spongy  substances  contain,  that  they  resist  the  passage  of 
heat  better  than  those  of  a  closer  texture.  Thus  eider-down, 
and  fur,  make  the  warmest  chxhing,  because  they  contain  the 
most  air  in  their  interstices,  and  ibr  the  same  reason  cotton 
batting  is  much  warmer  than  the  same  weight  of  cotton  cloth. 

Some  curious  experiments  were  made  by  Count  Rumiord  in 
1792,  for  the  purpose  of  ascertaining  the  relative  conducting 
power  of  materials  used  for  clothing.  He  arranged  a  ther- 
mometer in  the  interior  of  a  glass  cylinder,  having  a  bulb  blown 
at  one  extremity,  in  such  a  manner  that  the  bulb  of  the  ther- 

49.  What  did  Wiedemann  and  Franz  ascertain  in  regard  to  the  conducting  power  of 
bodies  for  heat  and  electricity  ?  Give  their  table.  Do  all  bodies  conduct  hent  with  equal 
f.iciiity  in  all  directions?  Give  the  exceptions  to  this  rule. — 50.  What  kind  of  conduc- 
tors are  porous  bodies?  To  what  is  their  non-conducting  power  due?  Def-'cribe  Count 
Ivuniford's  experiments  upon  the  relative  value  of  substances  used  for  clothing. 


CONDUCTION    OF    POROUS    BODIES.  29 

mometer  occupied  exactly  the  centre  of  the  bulb  of  the  cylin- 
der, and  filled  the  space  between  them  with  the  substances  to 
be  examined.  The  apparatus  was  then  dipped  iii  bo  ling 
water,  until  the  thermometer  marked  212°  in  every  case;  it 
was  then  transferred  to  melting  ice,  and  the  exact  time  con- 
sumed during  the  sinking  of  the  thermometer  through  135° 
noted.  When  there  was  nothing  but  air  between  the  thermom- 
eter and  the  cylinder,  the  cooling  took  place  in  576  seconds: 
wh3n  the  space  was  filled  with  twisted  silk,  in  917 ";  with  fine 
lint,  in  1032  ' ;  with  cotton  wool,  in  1046 ' ;  with  sheep's 
WOD!,  in  1118  ';  with  raw  silk,  in  1284 "  ;  with  beaver's  fur,  in 
1236'  ;  with  eider  down,  in  1305";  with  hare's  fur,  in  1315''. 
The  general  practice  of  mankind  is,  therefore,  fully  justified 
by  experiment.  In  winter,  the  animal  heat  is  retained  as  much 
as  possible  by  covering  the  body  with  bad  conductors,  such  as 
woolen  stuffs,  furs,  and  eider-down  ;  while  in  summer,  cotton  or 
linejt  is  used  for  the  purpose  of  increasing  as  much  as  possible 
the  escape  of  heat. 

The  imperfect  conducting  power  of  snow  also  arises  from  the 
above  cause.  When  newly  fallen,  a  great  proportion  of  its 
bulk  consists  of  the  air  which  it  contains,  as  may  be  readily 
proved  by  the  comparatively  small  quantity  of  water  it  produces 
when  melted.  Such  a  provision  was  designed  for  the  benefit  of 
man,  in  preventing  the  destruction,  during  the  cold  of  winter,  of 
delicate  shoots  and  roots  imbedded  in  the  earth.  Farmers,  in 
cold  climates,  always  lament  the  absence  of  snow  in  winter,  be- 
cause as  a  consequence,  the  frost  penetrates  to  a  great  depth, 
and  does  much  injury  to  the  grain  sown  the  previous  autumn. 
So  great  is  the  protecting  effect  of  snow,  that  in  Siberia,  it  is 
said,  when  the  temperature  of  the  air  has  been  70  below  the 
freezing  point,  that  of  the  earth,  under  the  snow,  has  seldom* 
been  colder  than  32°.  It  has  also  been  often  observed  that  the 
heaving  of  the  ground  by  frost  is  much  less  when  it  is  protected 
by  snow,  than  when  it  is  uncovered  and  exposed.  For  the 
same  reason,  many  substances  which,  in  the  solid  state,  are 
quite  good  conductors  of  heat,  when  reduced  to  powder,  become 
very  poor  conductors.  Thus  rock  crystal  is  a  better  conductor 
'than  bismuth  or  lead ;  but  if  the  crystal  be  reduced  to  powder, 
the  passage  of  heat  through  it  is  exceedingly  slow.  Rock  salt, 
when  in  the  solid  state,  allows  heat  to  pass  through  it  with 

Giva  his   results.     To  what  is  the  non-conducting  power  of  snow  owing  ?    What  ia 
the  ellect  of  pulverization  ou  conduction? 


30  ILLUSTRATIONS    OF    CONDUCTION. 

great  facility,  but  common  table  salt  in  fine  powder  obstructs 
its  pa.ssage  almost  entirely.  Sawdust,  powerfully  compressed, 
ailows  heat  to  p;i  s  through  it  with  the  same  iacili  y  as  solid 
wood  or'  the  same  kind,  but  when  loose  and  unconlmed,  it  is 
one  of  the  poorest  conductors  known. 

51.  Iilu3t;ra£ioa3  of  Conduction.      Our   ordinary  sensations 
every  day  convince  us  of  the  different  powers  of  various  sub- 
stances to  conduct  heat.     In   the  winter   the   articles  in   a  cold 
room  impart  very  different  sensations   to  the  hand.     A  pair  of 
tong>  wi:l  coidict   away  so   much   heat   as  to  give  a  painful 
sen  ation  of  cold;  while  a  piece  of  fur  or  flannel,  scarcely  feels 
cold  at  ail,  and  yet  both   are  of  the  same  temperature,  when 
tested  by  the  thermometer. 

A  piece  of  anthracite  coal  lighted  at  one  end,  can  not  be 
touched  with  impunity,  even  at  the  distance  of  six  inches  from 
the  source  of  heat,  while  a  piece  of  burning  charcoal  or  of 
flaming  wood  may  be  he'd  without  any  sensation  of  heat  at  ihe 
distance  of  only  1-20  of  a'.i  inch  from  the  flame.  Hot  water  in 
an  earthen  pitcher  will  feel  only  moderately  warm  on  account 
of  the  poor  conducting  po\ver  of  the  earthy  material  which  con- 
tains it,  while  the  same  water  poured  into  a  tin  cup  held  firmly 
in  the  hand,  will  be  found  too  hot  to  be  endured,  on  account  of 
the  excellent  conducting  power  of  the  tin.  A  saucepan,  having 
an  iron  handle,  can  with  difficulty  be  removed  from  the  fne 
with  the  naked  hand,  while  if  it  be  provided  with  a  handle  of 
wood  it  can  be  moved  with  ease.  The  large  amount  of  iron 
required  for  castings  of  great  size,  is  often  more  than  can 
be  melted  in  a  furnace  at  one  heating.  As  each  successive  fur- 
nace full  is  melted,  it  is  emptied  into  a  large  iron  vessel  eleA  atcd 
several  feet  above  the  ground,  and  having  a  conduit,  which  may 
be  opened  at  pleasure,  leading  from  the  lower  part  to  (he  mould 
embedded  in  the  earth.  This  vessel  has  a  lining  of  clay  or  fire 
brick,  and  the  melted  iron  is  also  covered  with  a  layer  of  fine 
charcoal.  In  consequence  of  the  extremely  poor  conducting 
power  of  this  substance,  and  of  the  earthen  lining  just  described, 
the  melted  iron  may  be  preserved  in  a  liquid  state  for  several 
hours,  until  a  sufficient  quantity  has  been  accumulated  to  make 
any  casting,  however  large. 

52.  Applications  in  the  Arts.  These  principles  admit  of  many 
useful  applications  in  the  arts,  and  explain  many  natural  phe- 

51.  Give  illustrations  of  conduction — the  tongs — tlie  carpet — anthracite  coal — tin  cup 
of  hot  water — iron  furnace  lined  with  fire-brick. 

I 


ILLUSTRATIONS    OF    CONDUCTION,  31 

nomena.  Thus,  stoves  are  lined  with  fire  brick,  of  bad  conduct- 
ing power,  for  the  purpose  of  preventing  the  iron  covering  from 
being  heated  too  hot.  Furnaces  are  lined  with  the  same  mate- 
rial to  prevent  the  heat  from  escaping ;  houses  are  built  of  non- 
conducting materials ;  locomotive  boilers  and  cylinders  are  pro- 
vided with  casings  of  wood ;  steam-pipes  are  bound  with  can- 
vas ;  instruments  used  in  the  fire  are  provided  with  wooden 
handles ;  tea-pots  are  made  of  earthera-ware,  or,  if  of  metal, 
are  handled  with  woolen  holders ;  and,  in  the  best  of  them,  the 
metallic  handles  are  separated  from  the  body  of  the  vessel  by 
bits  of  ivory,  (an  excellent  non-conductor,)  for  the  purpose  of 
preventing  the  transmission  of  the  heat.  On  the  same  princi- 
ple, metallic  articles  exposed  to  a  very  low  temperature  are 
never  handled  without  woolen  or  leather  gloves,  lest  the  heat 
of  the  hand  should  be  too  rapidly  abstracted  ;  or,  if  so  handled, 
they  are  provided  with  leather  or  woolen  coverings  of  their 
own. 

53.  Sand,  an  excellent  non-conductor,  is  placed  beneath  the 
hearths  of  fire-places,  to  guard  against  accidents  by  fire.  At 
the  siege  of  Gibraltar,  the  red-hot  balls  fired  by  the  English, 
were  carried  from  the  furnaces  to  the  guns  in  wooden  wheel- 
barrows protected  only  by  a  thin  covering  of  sand.  Ice  is  pre- 
vented fro:n  malting  in  summer  by  wrappers  of  flannel.  It  is 
also  exported  to  warm  countries,  and  conveyed  to  the  most  dis- 
tant portions  of  the  earth,  packed  in  saw-dust  and  shavings. 

Refrigerators  are  provided  with  double  walls,  between  which 
are  enclosed  shavings  of  cork  or  powdered  charcoal.  Fire 
proof  safes  have  also  double  walls,  the  space  between  them  be- 
ing filled  with  ground  plaster  of  Paris.  Near  the  summit  of 
Mount  Etna,  ice  has  been  discovered  beneath  currents  of  lava, 
which  have  poured  over  it  in  an  incandescent  state.  It 
was  prevented  from  melting  only  by  a  thin  layer  of  volcanic 
sand.  The  ice  gatherers  of  the  same  mountain,  export  their 
ice  to  Malta,  and  distribute  it  through  Sicily,  protected  by  en- 
velopes of  coarse  straw  matting.  Asbestos,  a  fibrous  mineral 
substance,  is  woven  into  an  incombustible  cloth  of  such  poor 
conducting  power  that  red  hot  iron  may  be  handled  with  gloves 
made  of  it. 

Glass  is  another  excellent  non-conductor ;  and  a  glass  tum- 
bler filled  with  hot  water  may  be  handled  with  impunity,  when 

52    State  some  of  the  applications  in  the  arts ;  stoves,  furnaces,  locomotive  boilers, 
&c.— 53.  Cannon  balls,  how  kept  red-hot?    Ice,    how  prevented  from,  melting ? 


32  ANIMALS  AND  PLANTS  PROTECTED 

a  metallic  vessel  filled  with  the^ame.  would  severely  burn  the 
hand.  This  property  of  glass  exposes  it  to  the  danger  of  crack- 
ing when  suddenly  heated.  The  surface  immediately  in  con- 
tact with  the  source  of  heat  expands ;  but  the  non-conducting 
power  of  the  glass  preventing  the  heat  from  passing  inward,  the 
inner  portions  remain  in  their  unexpanded  state,  and,  as  a  con- 
sequence, a  violent  separation  of  one  from  the '  other  is  apt  to 
take  place.  On  this  account,  glass  ought  never  to  be  suddenly 
exposed  to  a  high  degree  of  heat.  Both  surfaces  should  be 
heated,  if  possible,  at  the  same  moment,  and  when  once  thor- 
oughly heated  through,  the  glass  should  never  be  touched  with 
any  cold  metallic  substance  by  which  the  heat,  at  a  particular 
point,  might  be  suddenly  abstracted.  This  is  the  reason  why 
heated  glass  and  earthen  vessels,  filled  with  hot  substances,  are 
often  broken  by  being  heedlessly  placed  upon  the  head  of  a  nail 
which  happens  to  project  from  the  wooden  floor. 

So  poor  is  the  conducting  power  of  glass,  that  a  large,  red- 
hot  molten  mass  of  it  may  be  ladled  into  cold  water,  and  the 
interior  remain  visibly  red-hot  for  several  hours ;  and  if  a 
large  crucible  full  of  melted  glass  has  once  solidified  by  the 
decline  of  the  fire,  it  is  almost  impossible  to  melt  it  again. 
For  the  same  reason,  the  vitreous  matter  of  which  lava  is  com- 
posed is  a  long  time  in  cooling,  and  its  heat  is  given  out  so 
slowly  that  many  months  after  its  irruption,  eggs  may  be  cooked, 
and  water  boiled,  in  the  crevices  with  which  it  is  filled. 

54.  Animals  and  Plants  Protected  from  the  Cold  by  non- 
conducting- Coverings.  Nature  also  makes  use  of  the  same 
principles  in  her  operations.  Animals  are  protected  against 
the  excessive  cold  of  winter,  which  tends  to  reduce  their 
temperature  to  such  a  degree  as  to  destroy  life,  by  thick  furs, 
an  excellent  non-conductor,  while  in  summer  these  are  ex- 
changed for  thinner  coverings. 

Birds,  which  from  their  rapid  and  lofty  flight,  are  especially 
exposed  to  a  dangerous  reduction  of  temperature,  are  covered 
with  feathers,  and  often  beneath  the  feathers,  with  fine  down, 
which  is  one  of  the  most  perfect  non-conductors  known.  The 
vegetable  kingdom  supplies  illustrations  of  the  same  principle. 
It  has  been  found  that  wood,  always  a  poor  conductor,  opposes 
much  greater  resistance  to  the  passage  of  heat  in  a  direction 

Illustrate  the  non-conducting  power  of  glass.  Explain  how  glass  may  remain  red- 
hot  in  water.— 54  How  are  animals  protected  from  the  cold  of  winter  ?  What  is  the 
advantage  of  the  non-conducting  power  of  wood  and  bark  ? 


BY    NON-CONDUCTIXG    MATERIALS.  33 

across  the  grain,  that  is,  from  the  centre  toward  the  bark,  than 
in  the  direction  of  its  length ;  it  is,  therefore,  difficult  for  the 
heat  to  escape  from  a  tree,  even  in  the  coldest  weather ;  and 
generally  the  temperature  of  the  interior,  near  the  pith,  is  much 
higher  than  that  of  the  cold  air  on  the  outside.  This  may  be 
shown  by  boring  a  hole  into  the  centre  of  a  tree,  on  a  cold 
winter's  day,  and  inserting  a  thermometer.  Indeed,  one  of  the 
most  important  offices  of  the  bark  is  to  confine  the  heat  as  much 
as  possible,  to  the  interior  of  the  tree ;  and  so,  instead  of  being 
dense  and  firm  like  the  woody  fibre  beneath,  it  is  porous  and 
spongy  in  its  texture,  so  as  to  enclose  a  large  amount  of  air. 
A  tree  stripped  of  its  bark,  is  liable  to  perish  from  loss  of  heat, 
like  an  animal  stripped  of  its  fur,  or  a  bird  of  its  plumage. 
The  general  effect  of  this  provision  of  nature  is  to  maintain  the 
tree  at  a  uniform  temperature,  both  in  winter  and  summer.  In 
the  case  of  young  and  tender  trees,  it  is  usual  to  surround  them 
with  an  external  covering  of  straw,  for  the  purpose  of  still  fur- 
ther confining  the  heat,  and  guarding  them  against  the  effects 
of  severe  cold.  For  the  same  reason  this  substance  is  placed 
upon  garden  beds,  in  order  to  protect  the  flowering  plants  and 
roots. 

55.  Liquids  arc  Poor  Conductors  of  Hoat.  Liquids  are  ex- 
ceedingly poor  conductors  of  heat,  and  have  even  been  thought 
to  possess  no  conducting  power  whatever.  Their  slight  conduct- 
ing power  may  be  shown  in  the  following 
manner.  Into  a  vessel  of  water,  whose 
temperature  has  been  carefully  determined 
by  a  thermometer,  pour  a  little  sulphuric 
ether.  In  consequence  of  the  superior 
lightnes?  of  this  liquid,  it  will  float  upon 
the  surface  of  the  water,  without  mingling 
with  it.  Now  apply  a  lighted  match,  and 
when  the  flame  of  the  burning  ether  has 
entirely  gone  out,  the  water  will  be  found 
to  possess  precisely  the  same  temperature 
as  before,  which  could  not  be  the  case  if 
it  possessed  any  power  of  conducting  heat 
whatever.  Again,  if  a  delicate  thermome- 

Non^condu'tlng  Power  of  tei%    U3    in    F'9*    6>    be    PlaCed    in    a  Jai*    °f 

Liquids.  water,  with    its   upper  bulb  just   beneath 

How  are  trees  maintained  at  a  uniform  temperature  in  winter  and  summer?  What 
is  the  design  of  straw  covering  for  trees  and  plants  ? — 53.  What  is  the  conducting  power 
of  liquids  ?  How  can  their  feeble  conducting  power  be  shown  ?  Describe  the  experiment 
in  Fig.  6.  Describe  the  experiment  in  Tig.  7.  Describe  Dr.  Murray's  experiment. 


34  LIQUIDS    ARE    POOR    CONDUCTORS. 

the  surface,  and  a  small  quantity  of  sulphuric  ether  be  poured 
upon  the  water  and  inflamed,  intense  heat  will  be  produced,  but 
in  consequence  of  the  poor  conducting  power  of  the  water,  no 
effect  will  be  experienced  by  the  thermometer,  though  its  bulb 
be  no  more  than  one  twentieth  of  an  inch  distant  fi  om  the 
flame.  In  like  manner,  if  ice  be  formed  at  the  bottom  of  a  glass 
test  tube,  and  secured  in  its  place,  water  may  be  boiled  in  the 
upper  part  of  the  tube,  by  holding  it  in  an  inclined  position  in 
the  flame  of  a  spirit  lamp,  as  represented  in  Fig.  7,  without 

melting  the  ice  in   the  smallest 
FiS-  7<  degree.      Count  Rumford  found 

that  the  heat  from  a  hot  iron 
cylinder  could  not  pass  down- 
wards, through  a  thin  stratum  of 
olive  oil  not  more  than  two  tenths 
of  an  inch  in  thickness. 

By  other  experiments,  how- 
ever, it  has  been  ascertained  that, 
liquids  do  conduct  heat  to  a  very 
slight  degree.  Dr.  Murray  es- 
g  Power  of  Liquids,  tablished  this  fact  in  the  following 
manner.  At  the  bottom  of  a 
vessel  of  ice,  he  placed  a  delicate  thermometer,  in  a  horizontal 
position,  and  then  poured  in  olive  oil,  until  the  bulb  of  the 
thermometer  was  just  covered ;  a  second  vessel,  of  iron,  was 
then  introduced,  filled  with  boilmg  water,  and  secured  in  such 
a  position  that  it  almost  touched  the  bulb.  In  seven  and  a 
half  minutes  the  heat  from  the  boiling  water  had  been  con- 
ducted by  the  oil  to  the  bulb  of  the  thermometer,  in  sufficient 
amount  to  raise  the  temperature  from  32°  to  37^°. 

Under  ordinary  circumstances,  however,  liquids  may  be  con- 
sidered absolute  non-conductors  of  heat.  This  is  true  of  all 
liquids  except  mercury,  which,  from  its  metallic  nature,  conducts 
heat  with  great  facility,  and  is  an  exception  to  the  general  rule. 
56.  The  Gases  are  Poor  Conductors  of  Heat.  The  air 
and  other  aeriform  fluids  are,  in  like  manner,  exceedingly  poor 
conductors  of  heat.  This  may  be  shown  by  the  operation  of 
double  windows.  A  thin  stratum  of  air  being  confined  between 
the  opposite  sashes  in  such  a  way  that  it  can  not  escape,  and  all 
communication  with  the  external  air  being  cut  off,  has  the  effect 

5fi   What  is  the  conducting  power  of  the  gases  ?    How  is  their  feeble  conduction  shovm 
by  double  windows  ? 


GASES    ARE    POOR     CONDUCTORS.  35 

of  preventing  the  passage  of  heat  from  the  inside  to  the  out- 
eide  of  the  window,  or  the  reverse.  The  internal  heat  is  pre- 
vented from  escaping,  and  the  external  heat  from  entering,  and 
consequently  the  house  is  rendered  much  more  comfortable 
in  both  winter  and  summer.  The  same  fact  is  also  proved  by 
the  construction  of  ice  pitchers,  which  are  really  made  double,  and 
consist  of  a  pitcher  within  a  pitcher.  The  stratum  of  air  en- 
closed between  them  is  found  to  be  an  excellent  non-conductor 
of  heat,  and  to  obstruct  the  passage  of  the  external  heat  into 
the  pitcher  almost  altogether.  The  same  fact  is  also  illustrated 
by  the  double  roofs  of  ice-houses,  and  double  walls  of  fire-proof 
vessels  and  safes.  Double  walls  to  houses  make  them  much 
wanner  in  winter  by  preventing  the  escape  of  heat,  and  much 
cooler  in  summer  by  obstructing  its  entrance.  In  all  these 
cases  it  is  essential  that  the  air  be  c-osely  confined,  and  that  no 
opportunity  be  allowed  for  the  establishment  of  currents,  by 
openings  above  and  below ;  otherwise  the  escape  of  heat  is  fa- 
cilitated. The  non-conducting  power  of  air  is  also  shown  by 
the  poor  conduction  of  heat  by  substances  which,  like  fur  and 
down,  contain  a  large  quantity  of  it  inclosed  in  their  texture. 

57.  The  Conducting-  Power  of  Diucjeut  Gases  suppled 
to  be  different.  It  has  been  asserted  that  the  conducting  power 
of  the  gases  for  heat  is  very  unequal.  This  opinion  is  founded 
upon  the  different  cooling  effects  exerted  by  the  various  gases 
upon  the  temperature  of  a  platinum  wire  heated  white  hot 
by  a  galvanic  battery.  Such  %  wire  is  cooled  more  rapidly 
when  surrounded  by  air  than  when  in  a  vacuum,  more  rapidly  by 
hydrogen  than  by  air,  and  less  rapidly  by  sulphurous  ac'd  gas 
and  chloro-hydric  acid  gas,  than  by  air.  Tnese  experiments 
were  performed  with  an  apparatus  represented  in  Ficj.  8. 
Let  o  be  a  glass  vessel,  which  can  be  exhausted  of  air  through 
the  lower  stop-cock,  s  ;  let  s  be  another  stop-cock,  by  which 
air  or  any  other  gas  may  be  introduced  into  the  vessel  at  plea-- 
ure ;  b  is  a  metallic  rod,  passing  through  a  stuffing  box  air- 
tight, yet  capable  of  sliding  so  that  it  can  be  adjusted  at  any 
height ;  c  is  a  similar  metallic  rod,  connected  with  the  bra^s 
cap  at  the  lower  part  of  the  vessel ;  p  n  is  a  fine  platinum 
wire  by  which  b  and  c  are  now  connected.  The  glass  vessel 
being  full  of  air,  the  connections  with  the  poles  of  the  galvanic 
battery  are  formed  at  b  and  c ,  and  in  a  few  moments  the  heat 


By  ice  pitchers ?     By  ice  houses?     By  furs?     Why  is  it  necessary  that  the  air  should 
be  closely  confined  in  these  cases? — 57.  Is  tiie  conducting  power  of  gu&es  for  heat  cuu;.l  ? 


36 


GASES    DIFFER    IN    CONDUCTING   POWER. 


Fig.  8.  is  great  enough  to  make  the  platinum  wire 

faintly  luminous.  Let  the  air  now  be  with- 
drawn by  an  air  pump,  arid  the  wire  almost 
in  an  instant  glows  more  brightly :  introduce 
the  air  again,  and  it  glows  more  feebly.  This 
reduction  of  temperature  from  a  while  heat  to 
bright  redness  seems  to  show  that  the  air,  when 
it  is  readmitted,  has  ,<o  much  conducting  power 
for  heat  as  to  lower  the  temperature  of  the 
wire  very  sensibly.  Now  let  the  vessel  be 
exhausted  a  second  time,  and  in  place  of  air, 
let  Hydrogen  gas  be  introduced :  the  wire, 
which  began  to  glow  with  a  white  heat  on 
the  exhaustion  of  the  air,  as  soon  as  this  gas 
is  introduced  ceases  to  glow  altogether,  and  it 
will  be  necessary  to  more  than  double  the 
power  of  the  battery  in  order  to  raise  the 
wire  again  to  a  white  heat.  This  seems  to 
show  that  the  conducting  power  of  Hydrogen 
for  heat  is  much  greater  than  that  of  air. 
Different  Conducting  If  the  Hydrogen  were  withdrawn,  the  energy 

Power  of  Gases.        Qf    ^    current    wou]d    nQW    be    great    enough 

to  fuse  the  wire.  The  cooling  effect  of  the  other  gases  may  be 
ascertained  in  the  same  way.  Illuminating  gas,  ammonia,  and 
the  vapors  of  alcohol  and  ether,  also  exert  a  greater  cooling 
influence  upon  such  a  wire  than  air.  It  has  also  been  found 
that  if  heat  be  applied  at  the  closed  top  of  a  vessel,  it  is  conveyed 
more  quickly  to  a  thermometer  placed  at  some  distance  from  the 
top  when  the  vessel  is  filled  wiih  Hydrogen,  than  when  it  is  filled 
with  air.  This  is  the  case  even  when  the  vessel  is  loosely 
packed  with  cotton  wool  or  eider  down.  From  these  experi- 
ments it  has  been  argued  that  Hydrogen  conducts  heat  like  a 
metal.  On  the  other  hand  it  is  contended  that  Hydrogen,  being 
the  lightest  of  the  gases  and  more  than  fourteen  times  lighter 
than  air,  this  effect  may  be  due  to  the  superior  mobility  of  its 
particles  over  those  of  air.  This  would  hardly  seem  adequate 
to  account  for  all  the  effects  observed,  and  on  the  whole  it  would 
appear  that  the  gases  do  differ  somewhat  in  their  power  of  con- 
ducting heat. 


Describe  the  experiments  illustrated  by  Fig.  8.    What  is  the  general  conclusion? 


CONVECTION    IN    LIQUIDS. 


37 


Fig.  9. 


58.  The  second  mole  in  w!:i-h  heat  is  diffused  through 
bodies— Convection.     The  question  at  once  arises:  If  liquids  and 
gases  are  such  poor  conductors,  in  what  way  is  heat  propagated 
through  them  at  all  ?     Heat  is  conveyed  through  all  liquids  and 
ga^es  by  a  change  of  place  among  their  particles;  and  this  con-) 
stitutes  the  process  of  convection,  or  the  second  mode  by  which 
heat   seeks   an    equilibrium    and   is    diffused   through   matter. 
When  a  ve  ;sel  of  water  is  placed  over  a  fire,  the  particles  near- 
est the  flame  are  expanded,  and  becoming  specifically  lighter 
than  tho^e  around  and  above  them,  whose  temperature  is  a*  yet 
unaffected,  they  rise  to  the  surface.     At  the  same  time  the  cold 
particles  above  descend,  in  order  to  supply  their  place ;  these 
becoming  heated  in  turn,  also  rise  to  the  surface,  and  are  suc- 
ceeded by  a  fresh  supply  of  colder  particles  from  above.     In 
this  manner  all  the  water  is  gradually  brought  into  contact  with 
the  source  of  heat,  and  the  whole  mass  finally  becomes  uniformly 
wanned  throughout. 

59.  Convection  in  Liquids.     The  manner  in  which  liquids 

circulate  on  the  application  of  heat 
can  be  easily  shown.  Into  a  gla  s 
flask  containing  water,  see  Fig.  9, 
throw  a  small  quantity  of  any  inso- 
luble powder,  such  as  amber,  rosin, 
or  even  saw-dust,  as  nearly  as  possi- 
ble of  the  same  specific  gravity  with 
the  water.  When  placed  over  a 
lamp  the  circulation  will  soon  be. in  ; 
the  warm  currents  will  rise  in  the 
centre  where  the  heat  is  greatest, 
a  id  the  cold  will  descend  upon  the 
sides,  and  their  exact  direction  will 
be  indicated  by  the  so!id  particles 
which  they  carry  with  them.  The 
water  ascends  and  descends  in  this 
manner  just  the  same,  whether  the 
solid  particles  are  in  the  flask  or  not; 
these  only  serve  to  make  the  motion  more  plain  to  the  eye. 
Even  after  the  liquid  has  begun  to  boil,  this  same  circulation 
will  continue.  It  may  therefore  be  stated  as  a  general  truth, 
that  in  order  to  raise  the  temperature  of  liquids  and  make  them 


Convection  of  Heat  in  Liquids. 


58.  Describe  the  mode  in  which  heat  is  propagated  through  liquids.     What  is  convec- 
tion?— a9.  How  may  ta«  currents  produced  ia  liquids  b«  show.i  to  exist? 


38 


CONVECTION    IN    GASES. 


Fig.  10. 


boil,  heat  must  be  applied  at  the  bottom ;  they  can  not  be  heated 
from  the  upper  surface.  This  is  a  matter  of  great  practical 
importance  in  the  construction  of  the  boilers  of  steam  engines, 
and  in  all  ca^es  where  heat  is  to  be  diffused  through  large  quan- 
tities of  liquids. 

60.  Convection  in  Gases.    Similar  currents  are  established 

in  air  and  all  the  gases,  upon  the 
application  of  heat.  The  only 
difference  is,  that  the  heat  is  dif- 
fused through  them  with  much 
greater  rapidity  than  through 
liquids,  in  consequence  of  the 
superior  mobility  of  their  parti- 
cles. The  fact  of  the  establish- 
ment of  currents  in  air  by  the 
proximity  of  any  source  of  heat, 
is  clearly  shown  by  Fig.  10, 
where  a  lamp  chimney  is  repre- 
sented over  a  lighted  candle 
placed  upon  a  plate  filled  with 
water,  to  prevent  the  entrance 
of  air  from  below.  The  chim- 
ney is  divided  by  a  pasteboard 
partition,  and  on  dropping  a  bit 
of  smoking  paper  into  it  the 
movement  of  the  smoke  will 
show  that,  the  air  is  ascending 
on  one  side  of  the  chimney,  and 
descending  on  the  other,  exactly 
as  in  the  case  of  the  bits  of  float- 
ing amber  in  the  vessel  of  heat- 
ed water. 

61.  Illustrations  of  Convection.    The  existence  of  currents 
produced  by  convection  is  seen  on  a  great  scale  in  Nature,  in 
the  cases  of  the  Gulf  Stream  and  the  Trade  Winds.     The  air 
and  the  water  are  heated  in  both  these  cases,  not  by  the  direct 
rays  of  the  sun,  but  by  heat  which  emanates  from  the  earth. 
The  rays  of  heat  proceeding  from  the  sun  pass  through  the 
atmosphere  without  perceptibly  heating  it,  and  being  alb  orbed 
as  soon  as  they  strike  upon  the  earth's  surface,  graduallv  com- 

60.  How  is  heat  pro  ag-ited  through  gises?     HOT  may  fie  existence  of  currents  he 
•oved? — 61.  Give  illustrations  of  tue  existence  of  currcutj  iu   the 


Convection  of  Heat  in  Gases. 


pro 

tuo  ocean. 


atmosphere  aad 


ILLUSTRATIONS    OF    CONVECTION. 


39 


mnnicate  their  heat  to  the  lower  portions  of  the  atmosphere, 
and  to  the  water  immediately  in  contact  with  it.  These  heated 
particles  of  water  and  air  ascend,  in  consequence  of  th-jir  dimin- 
ished density,  and  as  their  places  are  supplied  by  descending 
currents  of  cold  water  and  air,  they  flow  otf  to  the  north  and  to 
the  south  of  the  equator,  carrying  the  heat  with  which  they  are 
charged,  and  imparting  it  to  the  cold  water  and  air  of  the  tem- 
perate regions;  while  on  the  other  hand  the  cold  water  and  air 
from  the  temperate  and  arctic  regions  are  drawn  steadily  toward •> 
the  tropics,  charged  with  the  cold  which  they  have  received 
from  the  poles.  There  is  therefore  a  current  of  hot  air  in  the 
upper  regions  of  the  atmosphere  setting  towards  the  north  and 
south  poles,  and  a  current  of  cold  air  near  the  surface  of  the 
earth,  moving  from  the  poles  to  the  tropics.  The  same  is  true  of 
the  waters  of  the  ocean;  a  current  of  warm  water  upon  the  sur- 
face is  setting  towards  the  north  and  south,  and  of  cold  water 
beneath  it  moving  from  the  north  and  south  towards  the  equa- 
tor;  see  Fig.  11.  Thus  the  excessive  heat  and  cold  of  the 


Fig.  11. 


Convection  Ulustiated  by  Trade  Winds  and  Gulf  Stream. 

>p03ite  portions  of  tho  earth  are  moderated,  and  the  general 


How  are  the  Trade  winds  produced?    The  Gulf  stream?    The  land  and  sea  breezes 
the  tropics? 


40  CAUSE    OF    CONVECTION. 

temperature  of  the  globe  rendered  more  nearly  equal.  To  the 
same  cause  the  sea  breezes,  which  temper  the  excessive  heat  of 
tropical  islands,  are  due.  The  hot  air  rising  from  the  heated 
surface  of  the  earth  floats  off  seaward,  and  the  colder  air  of  the 
sea  flows  in  near  the  surface  of  the  earth  to  supply  its  place : 
at  night  this  process  is  reversed ;  the  earth  being  colder  than 
the  sea,  the  warm  air  of  the  sea  flows  towards  the  land,  while 
the  cool  air  from  the  land  is  borne  out  to  the  ocean. 

62.  What  makes  the  heated  Water  and  Air  ascend?  As 
the  absolute  weight  of  the  heated  portions  of  liquids  and  ga-es 
is  not  diminished  by  the  increase  of  their  temperature,  the  ques- 
tion at  once  arises :  What  makes  them  ascend  ?  The  answer  to 
this  question  requires  an  accurate  knowledge  of  the  principles 
of  Hydrostatics,  for  which  reference  must  be  made  to  some 
good  treatise  on  Natural  Philosophy.  It  may  however  be  stated 
in  general,  that  the  heated  particles  rise,  because  their  density 
has  become  less  than  before,  and  less  than  that  of  the  colder  par- 
ticles immediately  around  and  above  them.  Take  for  instance 
the  case  of  a  cubic  inch  of  liquid,  near  the  bottom  of  a  flask 
of  water;  as  long  as  it  is  cold,  it  remains  at  rest  and  without 
any  tendency  to  move,  because  the  pressure  of  the  water  above 
it,  and  its  own  weight,  which  tend  to  make  it  sink,  are  exactly 
counterbalanced  by  the  pressure  from  below  tending  to  force 
it  upwards.  So  long  as  these  two  pressures  remain  exactly 
equal,  the  cubic  inch  of  water  will  continue  fixed  in  its  position ; 
but  let  the  equality  of  these  two  pressures  be  destroyed,  and  the 
cube  of  water  will  necessarily  move  in  one  direction  or  the 
other. 

These  two  pressures  may  be  represented  by  two  columns  of 
water  placed  side  by  side,  one  of  which  has  the  lower  surface 
of  the  cube  in  question  for  its  base,  and  extends  vertically  up- 
wards to  the  surface  of  the  water ;  the  other  is  placed  directly 
by  its  side,  and  possesses  a  ba?e  of  the  same  dimensions,  the 
same  altitude,  and  the  same  density.  Under  these  circumstan- 
ces the  cube  of  water  will  remain  in  equilibrium.  Let  this 
cube  be  now  enlarged  by  the  expansive  effects  of  heat  until  it 
has  attained  the  size  of  two  cubic  inches;  its  weight  remains 
exactly  the  same  as  before,  but  its  density  has  been  diminished 
one  half.  The  downward  pressure  is  now  represented  by  a  col- 
umn of  water  having  a  base  of  two  cubic  inches,  and  extending 
from  the  lower  surface  of  the  double  cube  of  water  in  question 

62.  Explain  tLe  ascension  of  heated  particles  of  liquids  and  gas«s. 


ASCENSION    OF    HEATED    LIQUIDS. 


41 


upwards  to  the  surface  of  the  liq-iid.  The  upward  pressure  is 
now  represented  by  a  column  or'  water  placed  by  the  side  of 
the  first,  also  having  a  base  of  two  cubic  inches,  and  extending 
upwards  to  the  surface  of  the  liquid.  These  two  pressures  are, 
however,  now  no  longer  equal,  because  the  densi  y  and  weight 
of  the  two  cubic  inches  at  the  base  of  the  first  column  are  only 
one  half  the  density  and  weight  of  the  two  cubic  inches  at  the 
base  of  the  seco.icl  column.  The  pressure  upwards  is  therefore 
greater  than  the  pressure  downwards  by  the  amount  of  this  dif- 
ference in  weight  between  the  two  lowest  cubic  inches  in  the 
second  column  and  the  two  lowest  cubic  inches  in  the  first. 
The  two  cubic  inches  of  expanded  water  will  therefore  be  pressed 
upwards  by  a  force  equal  to  this  difference  in  weight.  The 
cold  water  which  takes  its  place  will  undergo  the  same  process, 
and  rise  in  turn,  and  thus  a  steady  current  will  be  established 
which  will  continue  to  flow  until  the  water  has  acquired  the 
same  temperature  throughout,  or  the  source  of  heat  is  removed. 
This  is  also  the  cause  of  the  ascension  of  heated  air  and  of 
the  currents  that  are  established  in  the  atmosphere  when  brought 
into  contact  with  any  source  of  heat. 

63.    The  ascension  of  heated  Liquids  and  Gases  illustrated 
by  a  Figure.    This  process  is  illustrated  in  Fig.  12,  where  a  b 

and  c  d  represent  the 
two  columns  of  water 
which  exactly  balance 
each  other,  with  the  ex- 
ception of  the  two  cubic 
inches  at  the  base  of 
each.  A  cubic  inch  of 
cold  water  at  60°  weighs 
about  252  grs.  By  the 
application  of  heat,  such 
a  cubic  inch  has  been 
expanded  to  two  cubic 
inches  without  any  in- 
crease or  diminution  of 
its  weight.  The  two  cu- 
bic inches  of  hot  water 
weigh  precisely  the  same 
as  one  cubic  inch  of  cold 

Giuse  of  the  Ascension  of  Heated  Liquids  and  Gases.  Water;     their    density    IS 


Fig.    12. 

b.      c.      d. 


H.I 
252 

k 

grs. 

^^==i 

== 

Co 

252  + 
504 

Id 

252  = 
MT&J 

—  —  

-9 
-8 


63.  Explain  the  process  indicated  in  Fig.  12. 


42  RADIATION    OF   HEAT. 

therefore  diminished  one  half,  and  they  are  pressed  upwards 
by  the  particles  of  cold  water  about  them.  The  eqral  press- 
ure, therefore,  of  the  two  columns  a  b  and  c  d,  is  destroyed, 
in  consequence  of  the  inequality  in  the  weight  of  the  two  cubes 
at  the  base  of  each,  the  two  cubes  of  co.d  water  weighing 
252 -|- 252  =  504  grs.,  while  the  two  cubes  of  hot  water  weigh 
only  252  grs. ;  the  column  c  d  is  thus  made  heavier  than  a  />, 
and  tends  to  press  it  upwards.  The  importance  of  this  process 
of  convection  in  the  arts,  as  well  as  in  Nature,  can  not  be  too 
highly  estimated,  and  the  principle  on  which  it  depends  should 
be  thoroughly  understood. 

C-±.  Tne  third  mode  in  which  Heat  seeks  an  equilibrium 
—Radiation.  Radiation  is  the  name  applied  to  the  third  mode 
in  which  heat  seeks  to  distribute  itself  equally  through  bodies, 
viz.,  by  darting  from  a  hot  to  a  cold  body  through  an  appreciable 
interval  of  space. 

That  heat  is  so  transmitted  is  easily  proved  by  standing  be- 
fore a  fire,  or  holding  one's  hand  at  some  distance  from  a  hot 
body  suspended  in  the  air.  In  both  these  cases  it  is  clear  that 
the  heat  is  not  transmitted  by  conduction  from  particle  to  parti- 
cle of  the  intervening  air,  because,  as  we  have  seen,  the  con- 
ducting power  of  air  is  extremely  small ;  nor  is  it  by  convection, 
for  this  would  only  tend  to  propagate  the  heat  vertically,  by  the 
establishment  of  an  upward  current :  moreover  it  is  found  that 
the  process  goes  on  in  a  vacuum  with  three  times  the  rapidity 
that  it  does  in  air;  consequently  we  infer  that  no  medium  what- 
ever is  necessary  for  the  passage  of  heat  by  this  process. 

It  is  called  radiation  because  the  rays  of  heat  proceed  from 
every  point  upon  the  surface  of  the  body  equally  in  all  direc- 
tions, like  radii  from  the  centre  of  a  circle,  The  fact  of  radia- 
tion may  also  be  proved  more  satisfactorily  by  placing  several 
thermometers  at  equal  distances  from  a  hot  body  which  is  sus- 
pended in  the  air.  They  will  begin  to  rise  at  the  same  moment, 
and  at  the  expiration  of  a  given  time  will  all  be  found  to  indi- 
cate the  same  temperature,  with  the  exception  of  the  one  placed 
immediately  above  the  ball.  This  wrill  be  found  to  stand  higher 
than  the  others,  because  it  has  been  influenced  by  the  ascending 
currents  of  hot  air  produced  by  convection,  as  well  as  by  the 
rays  of  heat  which  have  reached  it  by  radiation.  If  the  ex- 
periment were  performed  in  a  vacuum  the  thermometers  would 
all  be  affected  equally. 

64.  What  is  the  third  mode  in  whirh  heat  seeks  an  equilibrium  ?  Is  any  med'um. 
necessary?  Why  called  Radiation?  How  may  the  foot  ot  radiation  be  proved?  Why 
does  the  upper  thermometer  stand  higher  than  the  others  ? 


LAWS    OF    RADIATION.  43 

65.  Radiant  Heat  follows  the  same  laws  as  radiant  Light. 
Rays  of  heat  proceed  irom  the  hot  body  in  right  lines  like  rays 
of  light,  and  with  a  velocity  equal  to  that  of  light;  and  their 
effect  diminishes  as  they  recede  from  the  hot  body,  not  in  pro- 
portion to  the  distance,  but  to  the  square  of  the  distance.     A 
thermometer  at  two  feet  from  the  radiant  body  will  not  indicate 
one  half  as  much  heat  as  the  thermometer  placed  at  the  distance 
of  one  foot,  but  only  one  fourth  as  much,  i.  e.,  four  times  less: 
in  this  respect  also,  radiant  heat  follows  the  same  law  as  light. 
When  radiant  heat  falls  upon*other  bodies  it  is  either  absorbed, 
— in  which  ca-e  it  rai;-e->  their  temperature, — or  it  is  reflected, 
i.  e.,  turned  back  towards  its  source  ;  or  it  is  refracted,  i.  e.,  bent 
out  of  its  originally  straight  course,  which  occurs  only  when  it 
falls  at  an  angle  less  than  a  right  angle,  upon  some  medium 
which  it  is  capable  of  traversing;    or  it  is  transmitted,  i.  e., 
parsed  through  unchanged  when  it  falls  perpendicularly  upon 
some  medium  capable  of  transmitting  it,  although  this  rarely 
takes  place  without  more  or  less  absorption.     Radiant  heat  does 
not  affect  the  temperature  of  the  media  through  which  it  pa-ses. 
A  tube  full  of  ether  may  be  held  in  the  focus  of  a  convex  lens 
wi  hout  becoming  sensibly  warmer,  but  if  any  of  the  rays  are 
absorbed  by  the  introduction  into  the  ether  of  some  Folid  sub- 
stance, such  as  a  bit  of  charcoal,  the  heat  thus  ab  orbed  is  com- 
municated ft  on  the  charcoal  to  the  liquid  by  convection ;  the 
ether  soon  begins  to  boil  and  is  finally  dissipated.     The  heating 
of  the  earth  by  the  sun  is  the  grandest  instance  of  radiation 
found  in  Nature.     The  heat  radiated  from  this  great  luminary 
parses  through  the  air  without  perceptibly  affecting  its  tempera- 
ture, and  finally  striking  upon  the  solid  earth,  is  absorbed  by  it. 
The  heat  thus  gained  by  the  earth  is  communicated  to  the  at- 
mosphere and  propagated  through  it  by  the  process  of  convec- 
tion, as  has  been  already  described.     The  amount  of  heat  radi- 
ated by  the  sun  in  the  course  of  a  single  day  upon  one  acre  of 
land  in  the  latitude  of  London,  is  estimated  to  be  equal  to  that 

j produced  by  the  combustion  of  one  hundred  and  eighty  bushels 
.of  coal. 

66.  The  nature  of  the  surface  affects  the  rate  of  Radiation. 
The  principal  fact  connected  with  radiation  is,  that  the  nature 
land  condition  of  the  surface  of  the  hot  body  has  a  powerful 


65  In  what  direction 'do  the  rays  of  heat  from  a  hot  body  proceed?  Tn  what  propor- 
tion docs  their  effect  diminish?  In  what  four  ways  is  radiant  heat,  when  it  fhlls  i^pon 
holies,  disposed  of?  Does  radiant  heat  :ilF-ct  the  temperature  of  ir-di-i  thror<r'i  v.-liich 
it  passes?  What  effect  does  it  produce  if  absorbed?  How  can  this  be  proved? — 66. 
What  influence  has  surface  upon  radiation  ? 


44 


EFFECT    OF    SURFACE. 


effect  in  promoting  or  checking  the  escape  of  heat  from  it  by 
this  process. 

Where  other  circumstances  are  equal,  the  rate  at  which  .heat 
escapes  from  bodies  by  radiation  is  directly  proportional  to  the 
roughness  and  dullness  of  their  surfaces,  and  in  the  inverse  pro- 
portion to  their  polish  and  smoothness  ;  in  other  words,  those 
surfaces  which  are  rough  and  dull  radiate  most  rapidly,  and 
those  which  are  bright  and  polished  most  slowly.  S'r  J.  Leslie, 
who  was  one  of  the  earliest  experimenters  upon  this  subject, 
ascertained  this  fact  by  the  following  experiment.  He  covered 
one  side  of  a  brightly  polished  cubical  tin  vessel  with  lampblack, 
another  with  writing  paper,  a  third  with  a  thin  plate  of  glass, 
while  the  highly  polished  surface  of  the  fourth  side  was  allowed 
to  remain  uncovered.  The  vessel  was  then  filled  with  boiling 
water,  tightly  closed  by  a  cork,  through  which  a  thermometer 
was  inserted,  and  placed  at  some  distance  before  a  concave  mir- 
ror having  a  delicate  differential  thermometer  in  its  focus,  some- 
what as  represented  in  Fig.  13.  The  radiating  effect  was  e&ti- 

Fig.  13. 


Effect  of  Surface  on  Radiation, 

mated  by  the  depression  of  the  thermometer  in  the  canister  and 

Describe  the  experiments  of  Leslie. 


CIRCUMSTANCES    AFFECTING    RADIATION.  45 

the  elevation  experienced  by  the  differential  thermometer  in  the 
focus  of  the  mirro;-.  On  turning  the  side  covered  with  lamp- 
black towards  the  mirror  the  thermometer  in  the  canister  soon 
sank  several  degrees,  while  the  one  in  the  focus  of  the  mirror 
ro  e  at  nearly  the  same  rate :  with  the  papered  side  the  effect 
upon  the  thermometer  was  nearly  the  same ;  with  the  glass  side 
the  effect  was  decidedly  less ;  and  with  the  bright  metallic  side 
the  influence  upon  the  thermometer  was  very  slight.  Taking 
the  quantity  of  heat  radiated  by  the  lampblack  as  100,  that 
radiated  by  the  paper  was  found  to  be  98,  that  by  the  glass  90, 
and  that  by  the  bright  metal  only  12.  From  this  experiment 
the  extremely  feeble  radiating  power  of  brightly  polished  metal- 
lic surfaces  is  very  apparent.  The  same  fact  can  be  readily 
shown  by  using  the  tin  cube  alone  without  the  mirror.  Ther- 
mometers placed  at  equal  distances  from  its  four  sides  will  be 
unequally  affected,  and  the  one  opposite  the  side  covered  with 
lampblack  will  rise  highest  in  a  given  time.  The  difference  in 
th y  amount  of  heat  radiated  can  be  readily  perceived  by  placing 
the  hand  successively  near  the  four  sides  of  the  vessel ;  the  im- 
pression produced  by  the  lampblack  side  will  be  decidedly  the 
mo-st  powerful.  This  experiment  may  bo  varied  by  u  ing,  in- 
stead of  one  vessel  with  differently  constructed  s'des,  three  can- 
isters of  sheet  bra^s,  having  exactly  the  same  dimensions,  but 
with  different  surfaces,  the  first  having  its  surface  highly  polished, 
the  second  covered  with  whiting,  the  third  with  lampblack,  fill- 
ing them  with  boiling  water  from  the  same  vessel,  and  then 
allowing  them  to  cool.  At  the  expiration  of  half  an  hour  the 
blackened  canister  will  be  found  by  the  thermometer  to  have 
lo^t  the  mo 4  heat,  and  to  have  the  lowest  temperature,  the 
whitened  canister  to  have  lost  somewhat  less,  and  the  polished 
oie  the  least.  Leslie  also  ascertained  that  by  roughening 
brightly  polished  metallic  surfaces  they  could  be  made  to  radi- 
ate nearly  as  well  as  lampb'ack ;  and  that  by  scratching  them 
with  lines  which  crossed  each  other  at  right  angles  the  effect 
could  be  greatly  increased.  This  is  probably  owing  to  the  in- 
crease of  the  amount  of  surface  exposed,  and  in  the  number  of 
radiating  points  thus  produced. 

67.  Other  circumstances  affecting-  the  rate  of  Radiation. 
It  ha.?  also  been  ascertained  that  a  variation  in  density  makes  a 
difference  in  the  amount  of  heat  radiated.  A  hammered  silver 
plate  will  radiate  much  less  than  a  cast  plate  of  the  same  metal. 

Describe  the  experiment  with  three  canisters.     Explain  the  effect  of  roughening  a 
polished  surface. — 67.  What  otaer  circumstances  affect  the  rate  of  radiation? 


46  APPLICATIONS. 

At  one  time  it  was  thought  that  color  also  had  an  effect  upon 
•radiation,  and  that  black  radiated  more  heat  than  any  oilier; 
but  ii:  ha?  now  been  ascertained  that  color  1ms  no  effect  what- 
ever o.i  radiating  power. 

68.  Kadiatiaa  also  talrcs  place  from  points  below  the  Sur- 
face.    It  has  also  been  found  that  radiation  does  rot  take  place 
solely  from  the  particles  which  compo.-e  the  surface  of  a  hot 
body,  but  that  it  also  takes  place  from  those  which  are  situated 
a  small  distance  beneath  the  surface.     This  was  ascertained  by 
Mr.  Leslie,  by  covering  one   side  of  a  vessel  containing  hot 
water  with  a  thin  coating  of  jelly,  and  putting  upon  another 
side  four  times  the  quantity.     The  nature  of  these  two  surfaces 
was  precisely  the  same  as  to  material  and  smoothness,  but  they 
were  found  to  radiate  very  differently ;  the   thinner  film  de- 
pressed the  thermometer  in  the  canister  38°,  while  the  thicker 
depressed  it  54°.     The  increase  of  radiation  continued  until  the 
coating  amounted  to  the  thickness  of  1 -1000th  of  an  inch,  after 
which  no  further  increase  took  place. 

69.  Practical  Applications.    Vessels  intended  to  preserve 
liquids  at  a  higher  temperature  than  that  of  the  surrounding 
air  for  as  long  a  time  as  possible,  should  be  provided  with  bad 
radiating  surfaces.     Water  in  a  bright  silver  tea-pot  will  retain 
heat  much  longer  than  one  made  of  earthen-ware  or  porcelain. 
A  tea-kettle  is  in  its  mo  t  efficient  state  when  its  bottom  is  blrck 
and  rough  with  soot,  and  its  sides  and  top  brightly  burnished, 
because  then  the  parts  exposed  to  the  fire  are  in  the  best  con- 
dition for  receiving  heat,  and  those  exposed  to  the  air  in  the 
best  condition  for  preventing  its  escape.     For  the  same  reason 
the  exposed  portions  of  locomotives,  such  as  the  cylinders  and 
steam  dome,  which  require  to  be  maintained  at  a  temperature 
considerably  higher  than  212°,  and  which  are  much  cooled  by 
rapid  motion  through  the  air,  are  covered  with  burni?hed  brass 
in  order  to  prevent  the  escape  of  heat,  and  are  kept  brightly 
polished,  not  so  much  for  ornament  as  for  utility.     There  is 
also  generally  a  space  of  several  inches  between  the  outside 
covering  and  ilv-i  true  surface  of  the  cylinder  and  of  the  dome  ; 
and  this  is  either  filled  with  confined  air,  which,  as  we  have  seen, 
i ;  a  poor  conductor  of  heat,  or  stuffed  with  some  non-conducting 
solid  substance,  such  as  felt,  wool,  or  shavings  of  wood,  in  order 
to  oppose  an  effectual  barrier  (o  the  escape  of  heat.     Pipes  iii- 

63.  Prove  thnt  radiation  inav  even  tike  place  from  points  beneath  the  su-fhce. — 09. 
State  the  practical  applications  of  the  principles  of  radiatiou.  How  is  the  heat  of  the 
locomotive  prevented  from  escaping? 


RADIATION    OF    THE    EARTH.  47 

tended  for  the  conveyance  of  hot  water,  steam,  or  heated  air  to 
a  distance,  should  be  kept  perfectly  bright  and  highly  polished  : 
but  when  they  are  designed  to  impart  heat  rapidly  to  the  sur- 
rounding air  they  should  be  roughened,  or  coated  with  some 
good  radiating  substance.  Stoves  and  stove-pipes  should  be 
made  of  rough  and  unpolished  iron  in  order  to  secure  the  great- 
est heating  effect ;  but  if  it  be  wished  to  carry  a  stove-pipe 
through  a  room  without  heating  it,  or  to  use  a  portable  furnace 
without  its  warming  the  room  in  which  it  is  placed,  they  should 
both  be  provided  with  a  brightly  polished  metallic  covering. 
By  attending  to  such  apparently  unimportant  circumstances  the 
consumption  of  fuel  may  be  greatly  economized. 

70.  The  Radiation  of  the  Earth.  As  the  earth  receives  its 
heat  from  the  sun  by  means  of  radiation,  so  it,  in  turn,  gives  out 
heat  itself  by  the  same  process.  When  the  sun  sets  and  the  influ- 
ence of  his  rays  is  withdrawn,  the  earth  then  becomes  a  radi- 
ating body  and  sends  forth  the  heat  which  it  had  acquired 
during  the  day  into  space ;  but  it  does  so  very  unequally. 
All  other  things  being  equal,  those  portions  of  its  surfa  *e 
which,  from  their  peculiar  conformation,  arc  good  radia'ors, 
send  forth  heat  much  more  freely,  and  are  more  reduced  in 
temperature,  than  those  which,  from  any  cause,  are  poor  radi- 
ators. Thus  a  bright  metallic  vessel  placed  upon  the  ground  at 
sunset  will  have  its  temperature  reduced  indeed,  but  not  nearly 
as  much  as  an  earthen-ware  dish  or  a  piece  of  wood  of  the  same 
size.  A  glass  cup  placed  in  a  silver  basin  which  ha^  been  left 
upon  the  ground  in  the  evening  will  become  much  colder  during 
the  night  than  the  basin  itself;  and  at  the  same  time  the  gracs 
and  leaves  of  plants  will  become  much  colder  than  the  smooth 
roads  and  paved  streets ;  rough  and  fuzzy  leaves  will  radiate 
more  heat,  and  beco.ne  much  colder,  than  those  which  have  a 
bright  and  polished  surface.  So  much  heat  is  thus  radiated 
that  on  a  clear  and  starry  night  the  earth  will  sometimes  be 
found,  by  a  thermometer  placed  upon  its  surface,  to  be  as  much 
as  seventeen  degrees  colder' than  the  air  ten  or  twelve  feet  above 
it.  -  There  is  a  close  connection  between  this  reduction  of  tem- 
perature and  the  formation  of  dew  and  frost,  for  the  e  are 
nothing  but  the  condensed  vapor  which  previously  existed  in 
the  air  in  an  invisible  form,  deposited  upon  different  substances 

What  surface  should  pipes  intended  to  convey  hot  steam  and  air  possess? — 7\  By 
what  process  does  the  earth  lo*e  its  heat  after  sunset?  Kxplain  the  reason  why  a 
rough  board  or  rough  leaf  becomes  cold%-  at  night  than  glass  aud  polished  metal 
State  the  connection  between  radiation  and  dew. 


48  REFLECTION    OF    HEAT. 

whose  temperature  has  been  reduced  by  radiation.  The  better 
the  radiating  surface  the  lower  will  be  its  temperature,  and  the 
greater  the  quantity  of  dew  and  frost  collected  upon  it.  This 
subject  will  be  more  fully  explained  when  we  come  to  speak 
particularly  of  the  watery  vapor  contained  in  the  atmosphere. 

71.  The  Theory  of  Radiation.     Two  theories  have  been 
proposed  to  account  for  the  phenomena  of  radiation,  suggested 
respectively  by  Pictet  and  Prevost.     According  to  the  former, 
when  bodies  of  unequal  temperature  are   brought  near  each 
other,  there  is  a  radiation  of  heat  from  the  hotter  to  the  colder, 
but  none  from  the  colder  to  the  hotter ;  this  continues  until 
they  have  both  reached  the  same  temperature,  when  all  radia- 
tion ceases.     Prevost,  on  the  contrary,  is  of  the  opinion  that  all 
bodies,  whatever  their  temperature,  are  constantly  emitting  rays 
of  heat  in  every  direction ;  that  the  temperature  of  a  body  falls 
whenever  it  radiates  more  heat  than  is  radiated  to  it ;  its  tem- 
perature is  stationary  when  it  receives  exactly  as  much  heat 
from  other  bodies  by  radiation  as  it  radiates  to  them,  and  that 
its  temperature  rises  when  it  receives  more  heat  than  it  radi- 
ates.    According  to  this  theory,  which  is  now  generally  adopted, 
all  bodies,  whatever  their  temperature,  are  continually  exchang- 
ing rays  of  heat  with  each  other ;  and  this  is  supported  by  the 
analogy  of  Light.     Luminous  bodies  mutually  exchange  rays 
of  light ;  a  feeble  light  sends  rays  to  one  of  greater  brightness, 
as  well  as  receives  rays  from  it;    and  the  quantity  of  light 
emitted  by  each  does  not  seem  to  be  influenced  by  the  vicinity 
of  the  other.     It  is  probable,  therefore,  that  the  radiation  of 
heat  takes  place  in  the  same  manner. 

72.  The  Reflection  of  Radiant  Heat.    When  radiant  heat 
falls  upon  a  solid  or  a  liquid  body  it  is  either  reflected,  absorbed, 
or  transmitted.     All  the  rays  which  are  not  absorbed  or  trans- 
mitted are  reflected.     The  fact  of  reflection  may  easily  be  proved 
by  standing  before  a  fire  in  such  a  position  that  the  heat  can  not 
reach  the  face  directly,  and  then  placing  a  piece  of  tinned  iron 
in  such  a  position  as  to  allow  of  seeing  the  fire  by  reflection ; 
'as  soon  as  it  is  brought  into  this  position  a  distinct  impression 
of  heat  will  be  perceived. 

73.  Law  of  Reflection.— Angles  of  Incidence  and  Reflection 
equal.     In  every  case  of  the  reflection  of  heat  the  angle  of  in- 
cidence is  equal  to  the  angle  of  reflection.     In  this  respect  heat 
follows  the  same  law  as  light.     This  law  has  long  been  known 

71.  State  Pictet's  theory  of  radiation.      Prevost's.      Give  the  analoprv  of  light.— 72. 
What  is  meant  by  the  reflection  of  heat  ? — 73.  State  the  law  of  Reflection. 


LAW    OF    REFLECTION.  49 

in  regard  to  heat  associated  with  light,  as  in  the  ca^e  of  the 
sun's  rays  anl  those  which  are  emitted  from  a  red-hot  ball;  but 
that  non-luminous  heat,  like  that  which  proceeds  from  vessels 
of  hot  water  or  from  other  bo.lie^  heated  be'.ow  redness, — that 
these  invisible  rays  of  heat  are  subject  to  the  same  law  of  re- 
flection as  those  which  are  accompanied  by  light,  is  a  modern 
discovery,  first  established  by  Saussure  an  I  Pictet,  at  Geneva. 
This  very  interesting  fact  maybe  proved  thus:  In  Fi<j.  14, 

let  m    n    be  a  mirror  of    tinned 
Vls- 14-  iron,  polished,  and  let  a  ball,  heat- 

ed to  any  degree  below  redness, 
be  placed  somewhere  upon  the 
line  A  B  ;  the  ray  of  heat  falling 
upon  the  mirror  will  be  reflected 
so  as  to  reach  a  thermometer 
placed  upon  the  line  c  B  ;  and 

ji.  B  ,llt      on  measuring  the  angle    ADD 

Law  of  Reflection.  which  the  incident  ray  makes  with 

the  perpendicular  at  the  point  of 

incidence,  it  will  b^  found  to  be  exactly  equal  to  the  angle  c 
B  D  which  the  reflected  ray  makes  with  the  same  perpendicu- 
lar. It  follows  from  this  law  that  with  a  concave  parabolic  mir- 
ror the  rays  of  non-liminous  heat,  like  those  of  light,  may  be  col- 
lected to  a  focus ;  and  with  two  such  mirrors,  some  very  inter- 
esting experiments  may  be  performed  illustrative  of  the  laws 
of  radiation,  as  well  as  those  of  reflection. 

74.  Concave  Mirrors.  Concave  mirrors,  or  reflectors,  are 
parabolic  or  spherical  surfaces  of  rnetal  or  glass,  which  serve  to 
concentrate  rays  of  light  or  heat  upon  one  point  called  the  focus. 
In  Fiq.  15,  a  section  is  given  of  a  spherical  mirror  of  this  de- 
scription. M  N  is  the  mirror,  A  is  its  middle  point  or  centre, 
c  is  the  centre  of  the  sphere  of  which  the  mirror  forms  a  part, 
and  A  B  is  a  line  perpendicular  to  the  middle  point  of  the 
mirror.  Now  upon  the  line  A  B  — the  principal  axis  of  the 
mirror — let  any  source  of  heat  be  placed  at  such  a  distance  that 
the  rays  E  K,P  H,G  I,L  D  can  be  considered  as  parallel 
to  each  other:  the  ray  E  K  falling  on  the  mirror  will  then  be 
reflected  in  such  a  direction  that  the  angle  c  K  F  ,  which  is 
the  angle  of  reflection,  will  be  equal  to  the  angle  c  K  E  ,  the 
angle  of  incidence ;  because  any  one  point,  as  K  ,  may  be  re- 

How  may  it  be  proved  in  the  case  of  a  plane  mirror? — 74.  Describe  the  concave  mir- 
ror. 


50  COXCAVE    MIRRORS. 

garded  as  a  plane  mirror,  and  the  line  c  K  is  a  perpendicular 
drawn  to  it.  All  the  other  rays,  p  H  ,  A  i ,  L  D  ,  will  be 
reflected  in  the  same  manner,  and  concentrated  upon  the  same 
point,  F  ,  situated  upon  the  line  A  B.  It  follows  in  consequence 
of  this  concentration,  that  there  will  be  a  greater  elevation  of 

Fig.  15. 


Refection  from  Curved  Surfaces 

temperature  at  F  than  at  any  other  point.  This  point  is  there- 
fore called  the  Focus,  and  F  A  ,  the  distance  from  the  focus  to 
the  centre  of  the  mirror,  the  focal  distance.  In  the  figure,  the 
rays  of  heat  are  passing  from  E  to  K  to  F  ,  in  the  direction  of 
the  arrows ;  but,  reciprocally,  if  the  hot  body  be  placed  at  F  , 
the  rays  of  heat  will  pass  from  F  to  K  ,  to  H  ,  to  A  ,  to  I ,  to  u  , 
and  from  these  points  be  reflected  in  lines  parallel  to  each  other ; 
should  the^e  rays  then  fall  upon  a  second  spherical  mirror  ex- 
actly opposite  to  the  first  they  will  be  reflected  a  second  time, 
and  concentrated  at  its  focus. 

75.  Experiments  on  Radiation  and  Reflection  with  two 
Concave  Mirrors.  Let  two  concave  mirrors,  made  of  polished 
brass,  and  from  twenty  to  thirty  inches  in  diameter,  be  placed 
exactly  opposite  to  each  other  and  ten  or  fifteen  feet  apart ;  Fig. 
16.  In  the  focus  of  one  mirror  place  a  flask  of  hot  water,  and 
in  that  of  the  other  a  thermometer,  with  a  screen  of  paper  or  glass 
between  them  ;  the  focus  of  mirrors  of  this  size  is  about  4^  or  5 
inches  from  their  centres.  Remove  the  screen,  and  the  ther- 
mometer will  at  once  begin  to  ri.-e.  If  a  cannon  ball  heated 
below  redness  be  employed  instead  of  the  bottle  of  hot  water, 
the  effect  upon  the  thermometer  will  be  more  decided.  That 
this  effect  is  due  not  to  direct  radiation  from  the  ball  to  the 
thermometer,  but  to  a  double  reflection  from  both  mirrors,  may 

Show  how  heat  is  reflected  by  it. — 75.  Describe  the  experiments  with  concave  mirrors. 


EXPERIMENTS    WITH    MIRRORS. 


51 


be  shown  by  moving  the  thermometer  from  the  focus  toward 
the  hot  ball,  when  it  will  be  seen  that  the  mercury  falls  instead 
of  rising ;  and  still  more  conclusively  by  placing  a  screen  fa- 
Fig.  16. 


N 


Reflection  of  Heat. 

tween  the  ho1  ball  and  its  mirror,  the  thermometer  being  in  the 
focus  of  the  other  mirror.  In  the  latter  case  there  is  an  opportu- 
nity for  direct  radiation  of  heat  from  the  ball  to  the  thermometer, 
but  none  for  reflection,  and  yet  the  mercury  falls ;  remove  the 
screen  so  as  to  allow  the  reflected  heat  to  fall  again  upon  the 
thermometer,  and  the  mercury  will  at  once  begin  to  rise,  show- 
ing that  the  effect  is  due  in  both  cases,  not  to  radiatron,  but  to 
reflection.  When  a  red  hot  ball  is  placed  in  the  focus  of  one 
mirror,  water  may  actually  be  boiled,  and  tinder,  phosphorus, 
and  gunpowder  ignited  in  the  focus  of  the  other.  Similar  ex- 
periments may  be  performed  with  a  piece  of  gilt  paper  rolled 
into  the  form  of  a  hollow  truncated  cone,  open  at  both  ends, 
the  metallic  surface  being  inside,  and  a  hot  ball  placed  opposite 
the  larger  opening  of  the  cone.  The  rays  of  heat  which  enter 

Show  that  the  effect  is  due  to  reflection,  and  not  to  direct  radiation. 


52 


REFLECTING    POWER    OF    DIFFERENT    SUBSTANCES. 


the  cone  will  be  reflected  in  such  a  way  as  to  be  concentrated 
at  a  tbcus  beyond  ihe  smaller  end,  in  which  phosphorus  and 
gunpowder  may  be  tired,  Fig.  17.  A  silver  spoon  held  in  sudi 

Fig.  17. 


Reflection  of  Heat  by  Gilt  Cone. 

a  position  before  the  fire  as  to  reflect  the  light  to  a  fo?ns  will 
al.-o  concentrate  the  rays  of  heat  to  such  a  degree  as  to  burn 
the  hand  and  scorch  a  piece  of  paper. 

76.  The  different  -Reflecting-  Powers  of  different  Substan- 
ces. This  was  determined  by  Mr.  Le4  e  with  an  apparatus  rep- 
resented in  Fig.  13  :  M  is  a  cube  of  boiling  water,  at  212°  ;  it  is 
placed  in  front  of  the  mirror  N  ,  on  a  lina  perpendicular  to  its 
middle  point.  The  rays  of  heat  proceeding  from  the  cube  are 
reflected  by  the  mirror  upon  a  plate  a  made  of  the  substance 
whose  reflecting  power  is  to  be  determined,  which  is  placed  ex- 
actly in  the  focus  of  the  mirror.  By  this  plate  the  rays  of  heat 
are  reflected  a  second  time  upon  the  bulb  of  a  differential  ther- 
mometer, and  the  number  of  rays  reflected,  or  the  reflecting 
power  of  the  plate,  is  measured  by  the  effect  which  is  produced 
upon  this  instrument.  Taking  the  reflecting  power  of  brass  as 
100,  it  was  found  by  this  process  that  silver  wa*  £0,  tin  80, 
steel  70,  lead  60,  Ind'a  ink  13,  glass  10,  oiled  glass  5,  g^s 
moistened  0,  lampblack  0.  Thus  it  was  proved  that  the  reflect- 
ing power  of  the  mrtals  is  much  greater  than  that  of  other 
bodies,  and  it  has  since  been  shown  by  Melloni  that  of  all  the 
metals  mercury  possesses  the  greatest  reflecting  power. 


Describe  the  experiment  with  cone  of  gilt  pnper. — 78-  Describe  Leslie's  experiments 
for  the  purpose  of  determining  the  relative  rellecting  power  of  different  substances. 
State  hiu  results. 


APPARENT  REFLECTION  OF  COLD.  53 

77.  The  apparsnt  Radiation  and  Rejection  cf  Cold.     There 
is  an  interesting  experiment  originally  pcribnned  by  ihe  Floivn- 
tine  Academicians,  which  seems  lo  prove  the  radiation  and  re- 
flection of  cold.     If  a  piece  of  ice  be  placed  in  ihe  fx'us  or' one 
of  the  mirrors,  a  thermometer  in  the  fojus  of  the  other  m'rror 
will  immediately  descend,  and  then  rise  again  as  .-ooa  as  the  ice 
is  removed.     From  this,  it  might  be  inferred  that  there  are 
frigorific  rays,  pos-es  ed  of  the  pawer  of  communica  ing  cold- 
ness-; but  it  is  evident  that  i'i  this  ca  e,  acco'ding  'o  the  theory 
o;'  M.  Provost,  the  thermometer  falb  because  it  radiates  more 
heat  than  it  receives,  and  not  in  co:i  equenee  of  the  influence 
of  frigorific  rays.     In   relation   to  the   ice  the  thermometer  is 
really  a  hot  bo.ly,  and  its  tempera" lire  sinks  when  placed  in  the 
focus  of  the  mirro:',  because  it  radiates  more   heat  to  the  ice 
than  is  radiated  to  it  by  the  ice:  as  ?oo;i  as  the  ice  is  removed 
the  thermometer  receives  as  much  heat  as  it  radiates,  and  its 
previous  tempera'ure  is  restored.     It  is  on  the  same  principle 
that  a  sensation  of  cold  is  experienced  on  approaching  a  wall 
or  a  building  whose  temperature  is  much  lower  than  our  bodies, 
viz.,  because  we  radiate  more  heat  than  we  receive. 

78.  The  material  of  which  BSirrors  are  made  aTects  their 
power  of  reflecting-  Heat.      There    is    a    remarkable    differ- 
ence between  the  substances  of  which  mirrors  are  made  wi:h 
respect   to  their  power  of  reflecting  heat,  though  their  polish 
may  be.  equal.     Thus  if  the?  experiments  already  described  be 
made  with  a  concave  glass  mirror  covered  in  the  usual  manner 
with  amalgam,  they  will  not  succeed.     A  red  hot  cannon  ball 
or  a  basket  of  burning  charcoal  placed  in  the  focus  of  such  a 
mirror  can  not  be  made  to  inflame  phosphorus  or  tinder  in  the 
focus  of  the  o  her.     The  mirrors  themselves  become  warm  and 
apparently  ab-orb  the  heat  without  reflecting  it,  while  they  re- 
flect light  in  the  usual  manner,  as  may  be  shown  by  substituting 
a  blackened  card  for  the  phosphorus  in  the  focus  of  one  of  the 
mirrors ;  a  bright  spot  of  light   will  immediate^  be  formed, 
which  is  evidently  the  result  of  reflection.     It  is  necessary  that 
mirrors  should  be  made  of  brightly  polished  metal  in  order  to 
reflect  bo'.h  light  and  heat.     If,  however,  solar  light  be  used  in 

•these  experiments,  instead  of  artificial  light,  it  is  found  that  glass 
mirrors  will  reflect  the  sun's  light  and  heat  without  becoming 

77.  What  effect  is  produced  if  ice  is  introduced  into  the  focus  of  one  mirror?  Does 
thi<  prove  tiie  radiition  and  reflection  of  cold? — 78.  What  effect  has  the  material  cf 
Avhic.i  the  mirrors  are.  made  .'  11'  t,oitir  light  be  employed,  does  the  material  of  tlie  mir- 
rors exert  auy  influence  ? 


54  PRACTICAL    APPLICATIONS. 

sensibly  warmed  themselves.  This  shows  that  the  source  from 
which  the  heat  proceeds,  as  well  as  the  material  of  which  the 
mirrors  are  made,  has  a  great  effect  upon  the  amount  of  heat 
reflected. 

75.  Practical  Applications.  The  power  that  brightly  pol- 
ished metallic  surfaces  pos  ess  of  throwing  off  the  rays  of  heat 
which  fall  upon  them,  i*  often  u  ed  for  the  purpose  of  protection 
against  high  temperature-,  and  for  preventing  bodies  from  be- 
coming dangerously  heated.  Thus  andirons,  if  brightly  polished, 
will  remain  comparatively  cool,  notwithstanding  their  proximity 
to  the  fire,  while,  if  rough  and  unpolished,  they  will  become  too 
hot  to  be  touched.  Water  contained  in  a  burni-hed  silver 
pitcher  can  with  difficulty  be  heated,  even  when  placed  directly 
before  the  fire:  the  same  amount  of  water  in  a  rough  iron  ket- 
tle at  an  equal  distance  from  the  fire  would  speedily  be  made 
to  boil.  Nor  is  it  necessary  that  the  protecting  sur.'ace  should 
be  of  any  great  thickness.  The  thinnest  coating  of  bright 
metal  reflects  he  it  as  perfectly  as  a  solid  metallic  plate  ;  a  mere 
covering  of  gold  leaf  will  enable  a  per.  0:1  to  place  his  finger 
within  a  very  small  distance  of  red  hot  iron  or  oilier  incan- 
descent body,  while  the  hand  would  be  burned  at  ten  times  the 
d'stance  if  unprotected.  If  a  piece  of  red  hot  iron  be  held  over 
a  sheet  of  paper  upon  which  some  letters  have  been  gilded,  the 
uncovered  intervals  will  bo  scorched,  while  the  letters  will  re- 
main un.arnished.  Wood  work  in  the  vicinity  of  stoves  and 
furnaces  can  be  perfectly  protected  by  a  covering  of  bright  tin. 
If  the  bulb  of  a  thermometer  be  coated  with  tin  foil  it  will  re- 
main comparatively  unaffected  by  changes  of  temperature. 
The  polished  metallic  helmet  and  cuirass  worn  by  soldiers  arc 
cooler  than  might  be  imagined,  because  the  polished  metal 
throws  off  the  rays  of  the  sun  and  can  not  easily  be  raised  to 
an  inconvenient  temperature. 

In  like  manner  heat  can  be  concentrated  by  reflection.  The 
Dutch  oven  reflects  the  heat  of  the  fire  upon  the  meat  placed 
within  it,  provided  its  inside  surface  be  kept  brightly  burnished. 
The  most  refractory  sub.rtances  can  be  melled,  and  even  the 
diamond  can  be  ignited  and  wholly  con:umed  in  the  focus  of  a 
concave  mirror,  placed  so  as  to  concentrate  the  full  strength  of 
the  solar  rays.  It  was  by  a  large  number  of  plane  mirrors, 
each  one  held  by  a  single  man,  and  so  adjusted  as  to  reflect  the 

79.  Describe  some  of  the  practical  applications  of  reflection  cf  heat.  Is  it  necessary 
th  .t  the  reflection,-  surf  ice  should  possess  any  great  thickness?  Describe  the  process 
by  which  Archimedes  set  fire  to  the  Roman  fleet. 


FIRE   PLACES. 


55 


heat  of  the  sun  upon  a  single  point,  that  Archimedes  is  said  to 
have  set  on  fire  the  Roman  fleet  before  Syracuse.  The  cele- 
brated French  Philosopher,  BufFon,  repeated  this  experiment  in 
the  last  century,  and  constructed  burning  mirrors  which  were 
able  to  accomplish  similar  results.  These  mirrors  were  made 
of  a  great  number  of  highly  polished  pieces  of  plane  glass, 
eight  inches  long  and  six  broad,  which  were  placed  in  such  a 
manner  that  the  rays  reflected  from  every  piece  could  be  concen- 
trated on  one  point.  By  employing  128  such  pieces  of  glass 
BufFon  succeeded,  at  a  distance  of  220  feet,  in  firing  a  pitched 
wooden  plank  by  the  heat  of  a  summer's  sun. 

80.  The  Reflection  of  Heat  by  Fire  Places.  The  first 
great  improvement  in  the  construction  of  fire-places  consisted 
in  building  the  sides  at  an  angle  to  the  back,  so  that  the  heat 
proceeding  from  the  fire  might  be  thrown  into  the  room  instead 
of  being  reflected  from  one  side  to  the  ofher  until  it  was  finally 
absorbed.  The  upper  part  of  the  back  of  the  fire-place  was 
also  inclined  forward  at  an  angle  to  the  lower  part,  for  the  same 
reason  and  for  the  purpose  of  contracting  the  throat  of  the 
chimney.  The  angles  of  inclination  should  be  135°,  as  repre- 
sented in  the  accompanying  figures,  and  the  brighter  the  sides 
and  the  back  of  the  fire-place  the  greater  the  amount  of  heat 
reflected  into  the  apartment.  The  ground  plan  of  the  old  con- 
struction is  represented  in  Fig.  18 ;  of  the  new,  in  Fig.  19. 


Fig.  18. 


Fig,  19. 


Old  Fire- Place. 


•  d' 
New  Fire-Flare. 


The  angle  of  incidence  is  the  angle  which  the  ray  of  heat  that 
falls  upon  the  side  of  the  fire-place  makes  with  the  line  drawn 
perpendicular  to  that  side  at  the  point  of  contact  of  the  incident 
ray,  ami  the  angle  of  reflection  being  equal  to  the  angle  of  inci- 
dence, it  is  evident  that  in  Fig.  19  the  incident  rays,  a  b  c  and 

Describe  Button's  repetition  of  this  experiment.— 80.  State  the  application  of  these 
principles  to  the  construction  of  fire-places. 


56 


ABSORPTION    OF    HEAT. 


tne 


Franklin's  Improvement. 


d  will  be  reflected  in  the  directions  a  b'  c  and  d' ,  and  thus 
find  their  way  into  the  room;  while  in  Fig.  18,  the  rays  must 
necessarily  lail  in  such  a  manner  upon  the  side  of  the  fire-place 
tnat  the  greater  part  of  them  will  be  reflected  from  one 
side  to  the  other,  until  they  are  ultimately  dissipated  and 
lost  in  the  chimney,  those  only  which  fail  perpendicularly  upon 
back  bemg  reflected  directly  into  the  room.  In  Fig.  20  is 

shown  the  same  fire-place  in 
elevation.  This  improvement 
was  made  by  Dr.  Franklin,  and 
is  found  in  the  oM-fashicned 
Franklin  stove,  which  \  ossesses 
alro  this  additional  advantage: 
that  all  the  heat  which  is  ab- 
sorbed by  the  iron  is  diffused 
through  the  air  of  the  apart- 
ment by  convection,  and  thus 
prevented  from  being  lost. 
Though  the  mode  of  warming  houses  by  means  of  fire-places 
has  nearly  passed  out  of  use,  this  improvement  of  Dr.  Frank- 
l:n's  deserves  to  be  remembered  as  being  truly  philosophical  in 
its  character.  It  would  greatly  conduce  to  the  r ublic  health  if 
our  houses  were  more  commonly  warmed  in  this  manner,  be- 
cause, by  keeping  up  a  continual  draught  it  favors  ventilation 
and  produces  a  mild  and  gentle  temperature. 

81.  The  Absorption  of  Radiant  Heat.  Bod'es  differ  very 
much  in  their  power  of  absorbing  radiant  heat.  The  absorbing 
power  of  a  body  is  always  in  the  inverse  proportion  of  its  re- 
flecting power;  if  it  be  a  good  reflector,  it  is  a  \oor  absoibcr, 
and  vice  versa.  To  determine  the  absorbing  ]  ower  of  bed  es, 
Leslie  made  use  o£  the  apparatus  which  he  employed  for  deter- 
mining their  reflective  power,  see  Fig.  13  ;  omitting  the  plate 
a ,  and  placing  the  bulb  of  the  thermometer  exactly  in  the 
focus  of  the  mirror.  This  bulb  was  covered  successively  with 
lampblack,  varnish,  gold,  silver  and  copper  leaf,  and  the  ther- 
mometer, under  the  influence  of  a  constant  source  of  heat,  M  , 
rose  or  fell,  as  the  substance  with  which  it  was  covered  ab.-oibed 
more  or  less  heat.  In  this  way  it  was  found  that  the  absorbing 
power  increased  as  the  reflecting  power  diminished.  It  was 
also  discovered  that  those  bodies  which  are  good  radiators  also 


81.  How  is  the  absorption  of  radiant  heat  determined?    What  is  its  relation  to  the 
pdwer  of  reflection  ? 


EFFECT    OF    COLOR    ON    ABSORPTION.  57 

absorb  heat  readily,  and  that  the  power  of  absorption  is  directly 
proportional  to  the  power  of  radiation.  Thus  lampblack,  which 
is  a  gioJ  radiator,  is  also  a  good  absorber;  and  in  general,  the 
more  ro  igh  and  uneven  the  surface,  the  more  freely  does  it 
allow  radiant  heat  to  enter  it. 

82.  The  Absorption  of  Heat  is  much  aTected  by  Color.    The 
color  of  a  body  has  a  great  effect  upon  its  ab  orbing  power. 
B:ack  absorbs  the  mo>t,  and  white  the  least.     This  fact  was 
first  noticed  by  Dr.  Franklin,  who  placed  pieces  of  different  col- 
ore;!  cloths  upon  the  snow  in  the  sunlight,  and  observed  that 
the  melting  extended  to  the  greatest  depth  under  those  which 
had   the   darkest  color.     If  pieces   of  copper   be    painted  of 
different  colors,  placed  upon   a   cake  of  wax  and  exposed  to 
the  sun,  a  similar  result  wi.l  follow.     If  the  bulb  of  a  ther- 
mo:neter  be  covered  with  paints  of  different  colors  and  pi  iced 
in  the  sun,  the  mercury  will  rise  the  highest  when  the  darkest 
colors  are  employed.     This  is  not  only  true  of  heat  associated 
with  light,  but  of  non-luminous  heat  also.     Thus  when  different 
colored  wools  were  wound  upon  the  bulb  of  a  thermometer,  and 
the  instrument  inclosed  in  a  glass  tube  immersed  in  hot  water 
at  212°,  it  was  fo  ind  that  the  effect  upon  the  thermometer  varied 
with  the  color  of  the  wool.     When  black  wool  was  used  the 
m  -rcury  rose  from  50°  to   1 70     in  4'  30  ' ;  dark  green,  in  5  ; 
scarlet,  in  5'  30"  ;  white,  in  8'.     Practical  application  is  made  of 
these  facts  in  the  selection  of  clothing ;  black  colors  should  not 
be   used  in  summer,   because    they   absorb   heat  re  tidily ;   but 
waite,   because    they    absorb    slightly   and   reflect   powerfully. 
B'aek  and  dark  colored  glass  may  be  used  with  advantage  in 
green-houses  and  hot-beds,  because  it  absorbs  heat,  and  elevates 
the  temperature  to  a  much  greater  extent  than  clear  and  train- 
parent  glass.     In   the   Alps,  the  mountaineers  accelerate   the 
me'ting  of  the  snow  by  scattering  earth,  ashes,  and  other  dark 
colored  sub^taiue?  upon  its  surface. 

83.  Transmission  of  Radiant  Heat.    When  radiant  heat  is 
not  reflected  or  ab  orbed  by  the  surfaces  on  which  it  falls,  it 
must  of  necessity  be  transmitted.     If  it  be  entirely  transmitted, 
no  elevation  of  temperature  is  produced  in  the  body  through 
which  it  p.is-e*.      There  are  but  few  substances,  however,  which 
thus  transmit  heat ;  generally  a  portion  of  it  is  absorbed,  and  an 
elevation  of  temperature  in  the  transmitting  bo;ly  produced. 

82.  Show  that  the  power  of  absorption  is  effected  by  color.     Is  non  luminous  heat  :if- 
ficted  in  the  same  manner?     How  can  this  be  proved?     State  some  of  tie  practical  np- 

f'ieations.  -83.   When  radimt  he:it  i*  not  reflected  or  absorbed,  what  becomes  of  it? 
f  iiej.t  be  entirely  transmitted,  wiia.t  «Ject  id  produced  upon  temperatiue  .' 


53  TRANSMISSION    OF    HEAT. 

84.  The  Transmission  of  Radiant  Heat  by  a-iy  substance 
d^pe  ids,  to  a  great  decree,  upon  the  source  from  which  ihe 
Heat  proceeds.  If  a  piece  of  glass  be  held  between  Ihe  buib 
of  a  thermometer  and  the  sun,  scarcely  any  diminution  of  tem- 
perature will  be  observed  in  the  thermometer,  and  scarcely  any 
elevation  of  temperature  in  the  glass  itself.  But  if  the  same 
plate  of  glass  be  held  between  a  brightly  burning  jire  and  the 
thermometer,  it  will  be  found  to  intercept  nearly  all  the  rays  of 
heat,  while  at  the  ?ame  time  its  own  temperature  will  be  greatly 
elevated.  The  common  glass  lens,  called  the  burning  gla-s, 
collects  the  heat  of  the  sun's  rays  to  a  focus  so  as  to  produce 
combustion  without  having  its  own  temperature  at  all  increased  , 
but  if  exposed  to  any  source  of  artificial  heat  and  light,  it  will 
collect  the  rays  of  light  to  a  focus  as  before,  but  will  not  con- 
centrate those  of  heat,  or  any  longer  pioduce  combust'on.  On 
the  contrary,  it  absorbs  the  rays  of  heat  as  last  as  they  fall  upon 
its  surface,  and  in  consequence  of  this,  its  temperature  rapidly 
ri-es.  In  like  manner,  with  a  lens  made  of  ice,  Mr.  Faraday 
succeeded  in  concentrating  the  sun's  rays  eo  as  to  inflame  gun- 
powder ;  but  the  same  lens  held  before  a  brightly  burning  lire, 
while  it  would  concentrate  the  light  as  befb;  e,  would  no  longer  al- 
low the  passage  of  the  heat ;  absorption  of  heat  at  once  took  place, 
and  the  lens  was  rapidly  melted.  In  like  manner  the  rays  of  the 
sun  may  be  so  concentrated  by  means  of  a  parabolic  mirror  as 
to  produce  a  bright  spot  of  light  and  inflame  a  combustible  sub- 
stance, or  even  fuse  metals  and  the  precious  stones,  and  if  a 
screen  of  glass  be  interposed  between  the  FUH  and  the  minor, 
or  between  the  mirror  and  the  substance  to  be  melted  or  burned, 
the  effect  will  be  but  little,  if  at  all,  diminished.  But  let  a 
powerful  lamp,  or  a  brightly  burning  fire,  be  substituted  in  place 
of  the  sun  in  this  experiment,  and  it  will  be  found,  on  inter- 
posing the  screen  of  glass,  that  the  heating  effect  of  the  mirror, 
instead  of  remaining  undiminished  as  before,  is  reduced  almost 
to  nothing,  while  the  brightness  of  the  spot  of  light  remains 
wholly  unchanged.  In  the  experiments  above  described  -upon 
the  radiation  and  reflection  of  heat  by  two  concave  minors, 
in  which  the  heat  is  derived  froin  some  artificial  source,  if 
a  screen  of  glass  be  interposed  between  them,  the  rays  of  heat 
will  be  entirely  intercepted,  and  the  glass  itself  become  sensi 


84.  la  there  any  connection  between  the  .amount  of  heat  transmitted  and  the  source 
from  which  it  proceeds?  Give  illustrations.  State  the  difference  between  solar  and  ter- 
restrial heat  as  to  concentration  b-/  a  lens.  What  experiment  may  be  performed  wUh  a 
lens  made  of  ice  ?  State  the  eHect  of  a  concave  mirror  upou  heat  proceeding  from  differ- 
ent sources. 


TRANSMISSION    OF    HEAT.  59 

bly  warmed.  For  this  reason  glass  is  preferred  to  every  other 
material  for  the  manufacture  of  tire  screens,  because  it  absorbs 
all  the  rays  of  heat  that  proceed  from  the  fire,  wi.hoat  ob- 
structing the  cheerful  light.  So  too,  it  is  used  to  fill  the  aper- 
tures for  observation  in  porcelain  and  metal  furnaces,  because 
on  account  of  its  transparency  it  allows  of  close  inspection  of 
what  is  passing  in  the  interior,  while  at  the  same  time,  in  con- 
sequence of  its  complete  absorption  of  the  rays  of  heat,  it  shields 
the  eyes  and  face  from  the  excessive  temperature  to  which  they 
would  otherwise  be  exposed.  It  is  not  to  be  understood,  however, 
that  perfectly  transparent  glass  is  absolutely  impermeable  to  ter- 
restrial heat,  but  only  that  its  power  of  tran -mission  is  very 
small.  The  intense  heat  of  charcoal  ignited  by  galvanic  elec- 
tricity does  produce  a  certain  effect  upon  the  air  thermometer 
when  concentrated  by  a  glass  lens,  and  thin  plates  of  glass  will 
also  slightly  transmit  the  heat  of  a  powerful  gas  burner. 

85.    Transmission  of  Radiant  Heat  of  equal  intensity  from 
differ  snt  sources  different  for  the  same  substance.    These  facts 
were  confirmed  by  some  experiments  made  by  Melloni,  an  Ital- 
ian philosopher,  who  paid  much  attention  to  this  subject.     In 
these   experiments   four   different   sources  of 
Fig.  21.          heat  were  employed,  viz. :  1st,  the  naked  flame 
of  an  oil  lamp ;   2d,  ignited  platinum  ;  od,  cop- 
per heated  to  750J  F. ;  and  4th,  copper  heated 
to  212°  F.     Although  these  different  sources 
differed  in  temperature,  the  experiments  were 
arranged  in  such  a  way  that  the  heat  proceed- 
ing from  each  was  in  all  cases  of  precisely 
equal    intensity ;    this    was    accomplished   by 
varying  the  distances  from  the  different  sour- 
ces of  heat  at  which  the  bodies  in  question  were 
Hffc  placed.     The  proper  points  were  determined  by 
noting  the  distances  at  which  a  differential  ther- 
mome  er,  Fiq.  21,  who-e  bulbs  were  covered 

Differential   T/ier-  •  i     i  111  -1-1          i  i  £• 

mometer.  with  lampblack,  was  required  to  be  placed  from 
each  ource  of  heat  in  order  to  rise  an  equal  num- 
ber of  degrees  in  the  same  time.  Then  thin  plates  of  rock  salt, 
fluor  spar,  alum,  and  other  substances  whose  power  of  trans- 
mission was  to  be  determined,  were  placed  in  turn  at  the  e 
ascertained  points  opposite  the  various  sources  of  heat  employed. 


Why  is  -glass  admirably  adapted  for  fire  screens?     Is  glass  impermeable  to  terrestrial 
heat  of  every  kind  ? — 85.  Give  an  account  of  the  experiments  of  Melloni. 


60 


TRANSMISSION    OF    HEAT. 


In  this  manner  the  heat  which  fell  upon  each  plate  from  every 
one  of  the  sources  employed  was  made  to  be  of  exactly  equal 
intensity.  Finally,  the  amount  of  heat  transmitted  by  each  sub- 
si  ance  was  ascertained  by  observing  the  effect  produced  upon  a 
delicate  thermo-multiplier  placed  in  succession  at  an  equal  distance 
from  each  plate  on  the  side  opposite  to  that  from  which  (he  heat 
proceeded.  The  results  are  contained  in  the  following  table. 
The  figures  not  only  indicate  the  comparative  capacity  of  differ- 
ent substances  for  transmitting  heat  from  the  some  source,  or 
their  diathermancy,  as  it  is  called,  but  also  demonstrate  the  re- 
markable fact  that  this  capacity  varies  in  mo$t  cases  with  the 
source  from  which  the  heat  proceeds,  notwithstanding  the  inten- 
sity of  the  heat  that  is  received  from  each  is  exactly  equal. 
The  explanation  of  this  singular  fact  is,  that  there  are  different 
kinds  of  heat  emitted  by  different  sources,  and  that  a  body 
which  is  permeable  to  one  kind  is  not  necessarily  so  to  all. 
The  only  exception  to  this  rule  is  found  in  rock  salt,  which, 
it  will  be  observed,  transmits  heat  equally  well  from  whatever 
source  it  may  proceed.  This  substance  is  in  all  cases  peri'ectiy 
transcalent  to  heat. 

Mellon? s  Table,  showing  t7ie  amount  of  Heat  from  different  sources,  but 
of  t/ie  same  intensity,  that  is  transmitted  by  different  substances. 


Each  Plate  was  0.102  inch  thick. 

Naked 
Flame. 

Ignited 
Platinum 

Topper 
7500  F. 

Topper 
2120  F. 

Rock  Salt,  limpid,    .         .         .' 
Sulphur,  Sicily,     ..'*». 
Fluor  Spar,       .         .         »'*>.,- 
Rock  Salt,  cloudy,         .    ,  .  ..^ 
Beryl,  greenish  yellow,     . 
Iceland  Spar, 
Phte  Ghsq 

92.3 

74 
72 
65 
46 
39 
39 

92.3 

77 
69 
65 
38 
28 
24 

92.3 
60 
42 
65 
24 
6 
g 

92.3 
54 
33 
65 
20 
0 
Q 

Quartz,  limpid, 
Quartz,  smoky, 
Topaz,  white, 
Tourmaline,      .... 
Citric  Acid,           .         . 
Alum,      
Sugar  Candv, 

38 
37 
33 
18 
11 
9 
8 

28 
28 
24 
16 
2 
2 
1 

6 
6 
4 
3 
0 
0 
0 

3 
3 
0 
0 
0 
0 
0 

These  experiments  establish  the  general  truth  that  the  amount 
of  heat  transmitted  by  any  substance  is  dependent,  to  a  certain 
extent,  upon  the  source  from  which  the  heat  proceeds.  Solar 


State  the  results  of  his  experiments.     Why  is  salt  called  a  perfect  diathermic  ?    Whaf 
important  truth  is  established  by  his  experiments  ? 


DIATHERMANCY 


61 


radiant  heat  finds  a  readier  passage  through  transmitting  meilia 
than  that  from  any  other  source. 

85.  Transmission  of  Radiant  Heat  from  the  same  source, 
di  ferent  far  diifereni  substances.  Diathermancy.  The  amount 
of  radiant  heat  transmitted  depends  not  only  upon  the  source 
from  which  the  heat  is  derived,  but  ako  upon  the  nature  of  the 
transmitting  substances.  Thus  the  rays  of  heat  from  a  brightly 
burning  fire  are  hardly  transmitted  at  all  by  a  piece  of  clean,  trans- 
parent, colorless  glass,  but  very  readily  by  a  piece  of  black  glass. 
Transparent  alum  is  nearly  as  impermeable  to  heat  as  colorless 
glass,  while  roc;k  salt,  which  is  almost  perfectly  opaque,  will 
transmit  it  with  the  greatest  readiness.  This  power  of  transmit- 
ting radiant  heat  is  called  Diathermancy.  Tho^e  bodies  which 
give  it  a  ready  passage  are  called  diathermanous,  while  those 
which  al'o.v  it  to  pass  with  difficulty,  or  intercept  it  altogether, 
are  called  adiathermanou*.  Rock  salt  is  the  most  perfect  dia- 
theivnano  is  body  known,  and  its  wonderful  power  in  this  respect 
caa  by  shown  by  the  apparatus  represented  in  Fig.  '2'2.  Let  s  be 

Fig.  22. 


Diathermancy  of  Rock  Salt. 

a  plate  of  rock  salt,  and  G  one  of  glass,  both  at  equal  distances 
from  the  ball  of  iron,  which  is  heated  nearly  to  redness.  Let 
P  p  be  bits  of  phosphorus,  supported  at  equal  distances  from 
the  plates  s  and  ft ,  behind  which  they  are  respectively  placed. 
The  plate  of  rcK-k  salt  is  four  times  thicker  than  the  plate  of 
glass,  and  is  also  nearly  opaque ;  but  notwithstanding  this,  the 


86.  Is  the  transmission  of  radiant  hent  from  the  same  source  the  same  for  all  media? 
ITo-.v  is  the  rel-ttive  diathermaucy  of  diifereat  solids  detcraiiued  ?  Describe  the  experi- 
ment illustrated  by  Fig.  2^. 


62  NOT    PROPORTIONED    TO    TRANSPARENCY. 

phosphorus  behind  it  will  be  inflamed  some  time  sooner  than 
that  which  is  behind  the  glass.  In  like  manner,  if  the  hands 
be  placed,  one  behind  each  plate,  the  difference  in  transmissive 
power  will  be  very  perceptible,  and  if  two  large  air  thermome- 
ters be  used,  this  difference  will  be  made  very  manifest  by  the 
rising  of  one  much  higher  than  the  other. 

87.  Diathermancy  is  not  proportioned  to   Transparency. 
Diathermancy  bears  the  same   relation   to  radiant    heat    that 
transparency  does  to  light.     Transparency  and  diathermancy 
are,  however,  by  no  means  proportional ;  on  the  contrary,  often 
the  most  transparent  substances  are  by  no  means  as  diatherma- 
nous  as  those  which  are  opaque.     Black  glass  will  allow  the 
rays  of  terrestrial  heat  to  pass  through  it  much  more  readily 
than  that  which  is  perfectly  clear  and  transparent.     Transparent 
alum  and  ice  intercept  the  rays  of  heat  almost  entirely,  while 
brown   roek   crystal    and    rock    salt,  which  are  quite  opaque, 
furnish  it  a  ready  passage.     Pure  water  arrests  radiant  heat 
almost  entirely,  while  the  reddish  liquid,  chloride  of  sulphur, 
allows  it  to  pass  with  freedom.     Sulphate  of  copper  allows  the 
passage  of  blue  light  abundantly,  but  arrests  the  rays  of  heat 
entirely.     Mechanical  arrangement  has  much   influence   upon 
diathermancy.     Pulverization  almo  t  completely  destroys  the 
power  of  transmitting  heat.     Rock  salt  powdered   is  almo-t 
completely  adiathermanous,  and  the  same  is  true  if  it  be  dis- 
solved in  water;  a  solution  of  rock  salt  is  nearly  as  adiatherma- 
nous as  a  solution  of  alum.     This  is  in  ana'ogy  with  the  effect  of 
change  in  mechanical   arrangement  uj  on    the  transmission  of 
light.     Pure  sugar  candy  is  transparent,  but  ground  to  powder, 
it  becomes  opaque ;  and  the  clearest  glass,  if  pulverized,  loses 
its  transparency  and  becomes  entirely  impervious  lo  light. 

88.  IVIcllonfs  experiments  on  the  Diathermancy  of  Solids. 
In  these  experiments,  from  which  the  greater  part  of  our  knowl- 
edge on  this  subject  is  derived,  the  heat  transmitted  was  meas- 
ured by  the  thermo-multiplier,  an  instrument  much  more  sensi- 
tive to  small  degrees  of  heat  than  any  thermometer.     It  is,  in 
fact,  the  most  delicate  measure  of  heat  known,  and  is  now  em- 
ployed   almost   exclusively  in    researches  of  this  description. 
The  principle  upon  which  it  is  constructed  is,  that  heat  has  the 
power  of  exciting  electricity,  and  the  more  intense  the  heat,  the 
. , 

87.  What  is  diathermancy?  Is  there  any  relation  between  diathermancy  and  trans- 
parency? Give  illustrations.  What  effect  has  mechanical  division  upon  diathermancy? 
Give  illustrations. — 88.  Describe  the  thermo-multiplier  used  by  Melloiii  in  his  experi- 
ments. 


DIATHERMANCY    OF    SOLIDS. 


63 


Fig.    23. 


more  powerful  the  current  of  electricity.  This  electricity  may 
be  measured  with  great  accuracy  by  the  galvanometer,  an  in- 
strument which  will  be  described  hereafter,  under  the  head  of 

e  1  e  c  t  r  o-magneti.-m.* 
The  general  arrange- 
ment of  Melloni's  ap- 
paratus may  be  seen 
in  Fiy.  23-,  G  is 
the  galvanometer,  l;y 
which  the  intensity 
of  the  electric  cur- 
rent is  measured ;  D 
c  represents  the 
thermo-electric  pile 
by  which  the  electri- 
city is  produced ;  T 
T  ,  are  cases  which 
fit  over  it  and  pro- 
tect it  from  the  influ- 
ence of  surrounding 
objects  ;  x  and  y 

Mdloni's  Apparatus.  are  wll'CS  which  CO11- 

vey  the  electricity  to 

the  galvanometer.  At  s  the  substance  is  placed,  who.-c  trans- 
missive  power  is  to  be  determined,  and  to  the  left  of  it,  but  un- 
represented m  the  figure,  stands  the  lamp  or  o  her  source  of 
heat  employed.  The  results  of  these  experiments  may  be  seen 
from  an  examination  of  the  different  columns  of  the  table  previ- 
ously given,  §  85.  Thus  in  the  first  column,  where  the  results 
are  tho^e  which  were  obtained  by  employing  the  naked  flame 
of  an  oil  lamp,  the  diathermancy  is  as  follows : 

Afellonfs  table  of  Diathermancy,  Stowing  iJie  amount  of  licat  from  the 
same  source  that  is  transmitted  by  different  substances. 

Each  Plate  was  0  102  inches  thick.     Source,  naked  Came. 


Rock  Salt,' 

92.33 

IQuartz,  limpid, 

83 

Sulphur, 

74 

Quartz,  smoky, 

9*1 

Fluor  Sp:ir, 

72 

'Topaz,  white,  . 

r.:j 

Jioek  Salt,  cloudy, 

65 

Tourmaline, 

13 

Beryl,  yellow  greenish,    . 

46 

Citric  Acid, 

11 

Iceland  Spar, 

39 

Alum,  .... 

9 

Pl.ite  Glass,      . 

39 

Sucfar  Candy,  . 

8 

64  DIATHERMANCY    OF    LIQUIDS. 

It  is  evident,  therefore,  that  substances  of  equal  transparency 
and  equal  thickness  differ  most  remarkably  in  their  power  of 
transmitting  heat  from  the  same  source.  Melioni's  apparatus 
was  so  deli.ate  that  the  heat  proceeding  from  the  hand  was  at 
once  made  apparent  by  its  effect  on  the  galvanometer,  and  a 
temperature  less  than  ^GV  of  a  degree,  F.,  could  readi'y  be 
deiec  ed.  It  is  the  only  instrument  with  which  experiments  of 
tli.s  kind  can  be  satisfactorily  periormed. 

09.  The  Diathermancy  of  Liquids.  In  like  manner  it  was 
ascertained  that  liquids  differ  very  much  in  their  power  of  tians- 
mitting  radiant  heat.  The  source  of  heat  was  an  argnnd  lamp, 
and  the  liquids  were  confined  in  a  trough  of  glass,  the  opposite 
faces  of  which  were  distant  fiom  each  other  0.362  of  an  inch. 
Turpentine  was  found  to  transmit  31  out  of  every  100  rays, 
while  rape  seed  oil  transmitted  but  30,  olive  oil  30,  ether  21, 
alcohol  15,  and  distilled  water  only  11.  Yet  all  thei-e  liquids 
are  almost  equally  transparent.  On  the  contrary  Chloride  of 
Sulphur,  which  is  of  a  reddish  color,  and  nearly  opaque,  allowed 
63  out  of  every  100  of  the  incident  rays  to  pass  thiough  it, 
showing  in  a  striking  manner  the  entire  independence  of  trans- 
parency and  diathermancy.  Pure  distilled  water  is  one  of  the 
mo^t  adiathermanous  liquids  known,  eighty-nine  per  cent,  of  the 
rays  of  heat  which  fall  upon  it  being  absorbed  without  percep- 
tibly raising  its  temperature.  A  beam  fiom  a  powerful  electric 
light  may  be  sent  through  a  mass  of  ice,  without  melting  it,  pro- 
vided the  light  be  first  made  to  pass  through  a  stratum  of  water. 
The  heat  seems  to  be  completely  strained  out  of  the  beam  and 
absorbed  by  the  water,  raising  its  temperature  speedily  nearly 
to  the  boiling  point,  while  the  light  passes  on  without  obstruc- 
tion. A  very  thin  stratum  of  water  is  quite  sufficient  to  cut  off 
all  the  heat  that  may  be  thrown  upon  it  without  perceptibly  in- 
terfering with  the  light.  It  therefore  makes  excellent  screens 
for  the  protection  of  workmen  from  the  excessive  temperatures 
of  furnaces,  while  at  the  same  time  it  allows  them  to  keep  a 
watchful  eye  upon  all  that  is  going  on  within.  In  consequence 
of  the  great  capacity  of  water  for  heat,  its  t(  mperature  is  but 
sllg'.itly  affected  by  the  heat  proceeding  from  common  sources. 

What  instrument  is  employed  to  measure  the  intensity  cf  the  heat?  Prove  the  ex- 
treme delicacy  of  tiiis  instrument.  Whstt  fraction  of  a  degree  can  be  measured  by  it? 
Give  the  general  results  of  Meiloni's  experiments  as  contained  in  the  table.— 89.  Is  the 
diathermancy  of  all  liquids  equal?  How  was  their  diathermancy  determined?  State 
the  diathermancy  of  several  important  liquids, — water.  a-Unhol,  ether.  Is  there  any 
ronnectioi  between  the  di  Uhennancy  and  transparency  of  liquids?  What  is  the  effect 
of  ke  arid  \v~ter  upon  raduut  he..t  ?  Why  do  they  make  excellent  scrteus  ? 


DIATHERMANCY    OF    GASES.  65 

90.  The  Diathermancy  of  Gases.  It  is  also  found  that  the 
different  gases,  though  they  may  be  equally  transparent,  trans- 
mit very  uneq  ml  quantities  of  terrestrial  raJiant  heat.  Per- 
fectly dry  and  pure  Air  appears  lo  transmit  all  the  heat  that  falls 
upon  it  without  the  slightest  absorption.  The  same  is  true  of 
Hydrogen,  Nitrogen  and  Oxygen.  But  Carbonic  Acid,  which 
is  equally  transparent  with  these  gases,  has  a  transmissive  power, 
Air  being  taken  as  1, of  only  £ff.  Tiie  Illuminating  gas  of  cities 
has  a  tr-msmissive  power  of  only  ff^.  Ammonia  TT\)5.  It  has 
also  been  found  that  moist  air  has  much  less  transmissive  power 
than  dry  air,  and  that  if  the  air  be  perfectly  saturated  with 
watery  vapor  its  transmissive  power  is  diminished  -£$.  The 
etfect  of  perfumes  diffused  through  the  air  is  the  same,  and  the 
vapor  of  alcohol,  ether  and  ammonia  produces  a  similar  result. 
It  is  the  elementary  gases,  i.  e  ,  those  which  are  incapable  of 
decomposition,  that  in  general  have  the  greatest  diathermancy 
and  the  least  absorptive  power.  The  compound  gases  and 
vapors,  on  the  other  hand,  possess  the  least  diathermancy,  and 
the  greatest  absorptive  power.  In  the  case  of  solids  it  has  been 
shown  that  good  absorbers  are  good  radiators.  The  same  is 
true  of  the  gases ;  those  of  them  which  have  the  least  diather- 
mancy, i.  e.,  tho;e  which  are  the  best  absorbers  of  radiant  heat, 
are  also  the  best  radia-ors,  and  allow  heat  to  escape  from  them 
most  readily.  The  amount  of  heat  transmitted  by  the  same 
gas,  under  the  same  circumstances,  depends  very  much  upon  the 
source  f,  o:n  which  the  heat  proceeds. 

The  d  athermancy  of  the  gases  mentioned  above  was  deter- 
mined with  heat  of  low  intensity,  and  derived  from  various 
terrestrial  sources.  The  heat  of  the  sun  passes  through  them 
With  much  less  absorption.  If,  however,  this  tolar  heat  be  al- 
lowed to  fall  upon  the  earth  it  is  radiated  again  as  terrestrial 
heat,  and  this  re-radiated  heat,  strange  to  say,  passes  with  great 
difficulty,  and  in  some  cases  is  entirely  unable  to  pass  at  all 
t' trough  the  air  and  other  transparent  media  which,  as  solar 
heat,  it  had  penetrated  with  the  greatest  ease.  The  moisture 
of  the  air,  which  then  had  little  power  to  obstruct  its  pa  sage, 
now  stops  it,  and  effectually  prevents  it  from  being  transmitted 
into  space  and  lost.  The  watery  vapor  in  the  atmosphere  has 


90.  Are  all  gases  equally  diathermanous?  What  is  the  difference  between  the  sim- 
p'e  ami  compound  puses  in  this  respect?  What  influence  does  the  source  of  heat  have 
upon  t  if  dhthorni;  ncv  of  gases?  What  effect  is  produced  upon  solar  heat  when  re  ra- 
di  ited  ;  f-ei-  absorption  b  the  e  irth  ?  What  effect  has  tiie  watery  vapor  of  the  air  upon 
the  escape  of  heat  from  the  earth  ? 


66  DIFFERENT    KINDS    OF   HEAT. 

the  Fame  effect,  therefore,  as  an  envelope  of  glass  would  have  in 
confining  the  heat,  which  tends  to  escape  from  the  earth,  while 
it  allows  a  free  passage  to  the  solar  radiant  heat  which  is  tend- 
ing towards  the  earth.  The  practical  utility  of  this,  in  main- 
taining the  earth's  temperature,  is  obvious.  In  the  same  way 
the  perfume  which  rises  from  a  flower-bed  prevents  the  escape 
of  a  large  proportion  of  the  radiant  heat  which  is  constantly 
striving  to  pass  from  the  earth,  and  thus  assists  materially  in 
keeping  the  soil  warm  and  productive.  This  must  have  a 
powerful  effect  upon  the  development  of  vegetation. 

91.  Diathermancy  explained  on  the  supposition  that  there 
are  different  kinds  of  Heat  analcgtms  to  the  different  colors  of 
Light.     The  reason  why  heat  of  a  certain  intensity  and  known 
effect,  proceeding  from  one  source  will   pass  readily  through 
certain  transparent  media,  while  heat  of  the  same  intensity  and 
the  same  effect,  as  estimated  by  the  thermometer,  but  proceed- 
ing from  a  different  source,  altogether  fails  to  pacs,  is,  that  there 
are  different  kinds  of  heat,  just  as  there  are  different  kinds  of 
light.     A  medium  which  will  transmit  one  kind  of  heat  will  not 
necessarily  transmit  another ;  just  as  one  piece  of  glass,  if  held 
up  to  -the  sun,  will  allow  only  the  red  rays  of  light  to  pass 
through  it,  absorbing  all  the  other  kinds,  while  another  pie<:e 
will  only  allow  the  green  rays  to  pass,  absorbing  all  the  others ; 
or  just  as  a  piece  of  red  glass  will  al!ow  all  the  light  from  flame 
of  a  red  color  to  pa°s  through  it,  but  will  not  allow  that  from 
flame  of  a  blue  or  green  color  to  pass  through  it  at  all.     The 
different  kinds  of  light  are  sufficiently  distinguished  from  each 
other  by  a  difference  in  color,  whicL  is  a  visible  property ;  the 
different  kinds  of  heat  not  being  thus  distinguished,  but  being  all 
equally  invisible,  it  is  necessary  to  resort  to  some  other  means 
of  distinguishing  them.     This  is  found  in  the  different  degrees 
to  which  they  are  bent  out  of  their  original  course,  or  the 
amount  of  refraction  they  undergo  when  passed  through  a  per- 
fectly transparent  prism  of  rock  salt.     This  substance  is  used 
both  because  it  is  the  most  perfect  of  all  diathermanous  sub- 
stances, and  also  because  it  u  equally  diathermanous  to  all  kinds 
of  heat. 

92.  The  existence  of  different  kinds  of  Heat  proved  by  the 
separation  of  a  beam  of  Solar  Heat  by  a  Prism  into  rays  pos- 
sessed of  different  Refra^gibility  and  different  heating-  power. 
When  the  rays  of  heat  fall  at  an  oblique  angle  upon  the  surface 

What  effect  have  perfumes? — 91.  What  reason  is  assigned  for  heat  from  different  sour- 
ces but  of  the  same  intensity,  passing  through  tne  same  medium  with  unequal  facility  ? 


PROVED    BY    THE  67 

of  any  substance  capable  of  transmitting  them,  they  arc  bent 
out  of  their  course  in  pas-ing  through,  or  in  olher  words,  are 
refracted.  The  law  of  refraction  for  heat  is*  very  nearly  the 
same  as  that  for  light.  This  is  proved  by  the  operation  of  the 
common  burning  glass,  for  it  refracts  both  the  heat  and  the 
1  ght  of  the  sun's  rays  to  nearly  the  same  degree,  and  concen- 
trates them  at  nearly  the  same  point,  so  that  the  brilliant  spot 
of  light  which  it  produces  is  also  the  point  of  greatest  intensity 
for  heat.  The  fact  of  the  refraction  of  rays  of  heat  may  al  o 
be  proved  by  the  use  of  a  triangular  glass  prism.  It  is  well 
known  that  if  a  beam  of  solar  light  be  transmitted  through  such 
a  prism,  it  is  separated  by  refraction  in'.o  several  rays  differing 
i»  color  and  refrangibility.  Thus  if  a  beam  of  sunlight  be 
allowed  to  enter  a  darkened  room  through  a  fine  slit,  and  fall 
upon  a  triangular  prism,  Fig.  24,  it  will  not  pass  through  the 

prism    in  a  straight 

lg*       line  and  form  a  bright 

spot  upon  a  screen 
of  the  same  size  as 
the  opening,  but  it 
will  be  bent  out  of 
its  course  and  throw 
upon  the  screen  an 
elongated  spot  cf 
light  compo  ed  of 

Decomposition  of  Ligkt.  "  different   colors,  ar- 

rang'-d  in  a  regular 
succession,  and  always  in  the  same  order.  This  eV.igated  spot 
of  light  is  called  the  solar  spectrum,  and  is  composed  of  the  fol- 
lowing colors :  violet,  indigo,  blue,  green,  yellow,  orange,  red. 
The  violet  rays  are  the  mo  it  refracted  from  the  original  course 
of  the  beam;  while  the  red  rays  are  the  least  refracted,  and  the 
highest  illuminating  effect  is  found  to  be  in  the  yellow  ray. 
Now  on  applying  a  delicate  thermometer  to  the  different  colored 
!rays  it  is  found  that  the  rays  of  heat  are  in  like  manner  not  col- 
lected at  one  point,  but  are  diffused  through  the  whole  spectrum, 
and  consequently  a  beam  of  solar  heat  is  composed  like  a  beam 
of  solar  light,  of  rays  of  heat  of  different  kinds,  and  possessed 
of  different  degrees  of  refrangibility.  It  is  also  found  that  as 

92.  Prove  that  there  are  different  kinds  of  heat.  How  are  the  diTerent  kinds  of  heat 
distinguished?  What  is  meant  hy  refraction  ?  What  is  the  law  of  refraction  for  heat? 
Describe  the  refraction  of  solar  light,  and  state  the  colors  produced.  Describe  tue  re- 
fraction of  heat. 


UNEQUAL    HEFIIANGIBILITY    OF    RAYS    OF   HEAT. 


the  rays  of  light  differ  in  color,  as  well  as  in  refrangibility,  so 
the  rays  of  heat  differ  not  only  in  refrangibility,  but  also  in 
t'-mperature.  Thus,  if  a  thermometer  placed  in  the  blue  ray 
of  the  spectrum  indicates  a  temperature  of  56 '',  when  brought 
down  into  the  yellow  ray  it  will  indicate  a  temperature  of  62°. 
If  it  be  moved  into  the  orange,  the  mercury  will  rise  still  higher, 
and  continue  to  indicate  a  steadily  increasing  temperature  as  it 
approaches  the  lower  part  of  the  spectrum,  until  it  finally  at- 
tains its  maximum  of  79°  in  the  extreme  lower  portion  of  the 
red  ray,  2o°  higher  than  in  the  blue,  and  17°  higher  than  in  the 
yellow  ray,  and  indicating  a  progressively  increasing  tempera- 
ture from  the  extreme  violet  to  the  extreme  red  end  of  the 
spectrum.  What  i.s  still  more  remarkable,  if  the  thermometer 
be  moved  to  a  point  below  the  red  ray,  and  entirely  outside  of 
the  spectrum,  it  will  be  found  to  rise  even  higher  than  in  the 
red  ray  itself,  and  a  certain  heating  effect  is  found  to  be  exerted 
at  a  point  very  considerably  below  the  limit  of  the  spectrum. 
This  is  shown  in  Fig.  25,  where  the  different  rays  of  heat 

marked  11.,  may  be  traced 

Fig.  25.  from  the  red    ray  of   the 

solar  spectrum,  u.,  as  far 
The  point  of 
heat    depends 
of   the 

substance  of  which  the 
prism  is  composed:  when 
made  of  crown  glass  it  is 
in  the  red  ray;  when  made 
of  flint  glass  it  is  just  b:  low 
the  red;  when  of  hollow 
glass,  filled  with  water,  it 
is  in  the  yellow  ray  ;  when 
made  of  rock-salt  it  is 
some  distance  below  the 
red  ray.  The  whole  range 
of  the  rays  of  heat  extends  from  v  to  6,  that  is,  through  all 
the  luminous  portion  of  the  spectrum,  and  also  through  a  space 
which  is  non-luminous.  These  results  of  Sir  W.  TIerschel  were 
confirmed  by  the  experiments  of  Sir  H.  Englefield,  who  proved 
that  the  thermometer  rose  in  the  different  rays  in  the  following 
order : 

Do  the  rays  of  heat  diPFor  in  temperature?  What  is  the  point  of  maximum  intensi- 
ty for  heat?  Is  it  ever  found  below  the  red?  Are  these  invisible  rays  of  heat  associ- 
ated with  solar  light  ? 


down  as  b. 

maximum 

upon   the   nature 


Unequal  refrangibility  of  the  Chemical,  Illumina- 
ting and  Heating  Rays  in  tfie  Solar  Beam. 


RATS  OF  HEAT  MAY  BE  SEPARATED.          69 

In  the  blue  rays,  in  3  min.,  from  35  J  to  5G"1,  or  1°. 
In  the  green  "  in  3  "  kv  54 3  to  OS  \  or  4\ 
In  the  yellow  "  in  3  "  "  50°  to  C2D,  or  6\ 
In  the  full  red  u  in  2i  "  "  50°  to  72 ^  or  10P. 
In  edge  of  red  "  in  ll\  "  "  58°  to  73J\  or  lo£°. 
Bolow  the  red  "  in  2J  "  "  61 D  to  79 -^  or  1SD. 

Sir  TV.  Herschel  ascertained  that  the  invisible  rays  exerted 
a  considerable  heating  power  at  a  point  1  ^  inches  distant  from 
the  extreme  red  ray,  even  though  the  thermometer  was  plac-ed 
at  a  distance  of  52  inches  from  the  prism.  From  this  it  is  evi- 
dent that  a  solar  beam  contains  rays  of  non-luminous  as  well  as 
luminous  heat,  the  former  being  much  less  refrangible  than  the 
latter;  or  rather  the  solar  beam  contains  rays  of  heat  mixed 
with  the  rays  of  light,  some  of  which  are  of  the  same,  and 
others  of  less  refrangibility  than  the  rays  of  light.  The  solar 
beam  also  contains  a  third  class  of  rays  more  refrangible  than 
those  of  heat  and  light,  possessed  neither  of  heat  nor  color,  but 
exerting  a  peculiar  chemical  power.  Of  these  we  do  not  now 
speak  particularly.  They  may  be  seen  in  Fig.  25,  extending 
from  v  to  Cj  and  inc'udcd  in  the  bracket  marked  c. 

C3.  Thi3  BLTcrc^co  is  so  marlred  that  we  may  separate  one' 
k'nd  of  H3at  from  others  with  which  it  is  mingled,  and  employ 
it  cKcluaively  at  our  plsasurs.  By  employing  a  lens  of  Rock 
Salt,  and  placing  it  in  the  bundle  of  invisible  rays  of  heat,  ex- 
tending from  R  to  b,  these  rays  may  all  be  gathered  up  and 
concentrated  at  one  focu-,  with  the  production  of  intense  lica^ 
but  without  a  particle  of  light,  and  thus  completely  separated 
from  tho.e  kinds  of  heat  of  greater  refrang'biiity  which  fall 
between  v  and  R  ,  and  are  mingled  \vi:h  the  rays  of  light  in 
the  luminous  part  of  tlie  spectrum.  Again,  there  are  some  sub- 
stances which  possess  the  remarkable  power  of  absorbing  all 
the  rays  of  light  contained  in  the  solar  beam,  but  transmitting 
all  the  rays  of  heat.  Glass  colored  black  by  carbon,  and  bi-?ul- 
phidc  of  carbon  containing  iodine  i  i  solution,  are  particularly 
distinguished  for  this  power.  Oa  transmitting  the  solar  beam 
through  the  latter  substance  the  rays  of  light  are  all  ab  orbed, 
airl  those  of  heat  alone  allowed  to  pass.  These  invisible  rays 
of  heat  thus  transmitted  may  al  o  be  concentrated  at  an  invisible 
focus  by  a  lens  of  Rock  Salt,  and  combustible  substances  actu- 
ally inflamed.  In  like  manner,  if  the  electric  light  produced  by 
the  passage  of  a  powerful  galvanic  current  between  pieces  of 
charcoal  be  employed,  instead  of  the  light  of  the  sun,  and  con- 

93  How  can  the  rays  of  heat  in  the  sun's  beam  be  separated  from  those  of  liiiht? 
What  etfects  can  be  produced  by  concentrating  the  invisible  rays  of  heat  by  means  of  u 
lens? 


0        THE  H::AT  OF  DirFzmixT  SOURCES  DIFFERENT. 

centratcd  at  a  fociis  by  a  concave  mirro",  the  intense  light  wh'ch 
is  omitte  I  will  be  entirely  ab  orbed  ly  ihe  «bovc-meniionf  d 
so'utio:i  of  iodine  in  bi-sulplildo  of  carl, on,  placed  between  the 
focus  of  the  mirror  and  the  charcoal  points,  and  the  rays  of  heat 
alone  allowed  to  pass.  These  invisible  rays  of  heat  will  still 
be  concentrated  at  the  same  focus,  as  before  the  solution  was  in- 
terposed, but  with  no  visible  mark  to  indicate  the  spot ;  the 
focus,  in  short,  will  be  entirely  invisible.  The  heat,  however, 
is  intense,  and  on  placing  in  this  dark  focus  pieces  of  wood  and 
paper,  they  are  immediately  inflamed, — lead,  tin  and  zinc  are 
melted;  if  the  invisible  focus  be  thrown  upon  a  piece  of  char- 
coal, su>pencL^d  in  a  receiver  of  oxygen  gas,  the  charcoal  will 
be  ignited  and  burn  with  splendid  scintillations ;  if  the  charcoal 
be  suspended  in  vacuo,  it  will  be  heated  red  hot.  If  blackened 
zinc  foil  be  placed  in  the  foeus  it  will  immediately  be  set  on 
fire,  and  burn  with  a  purple  flame ;  the  metal  magnesium  will 
burn  in  like  manner  with  a  splendid  light. 

94.  Different  kinds  of  Heat  are  emitted  by  different  sources 
of  Heat,  just  as  different  kinds  of  Light  are  emitted  by  different 
colored  Flames.  In  the  case  of  rays  of  light,  if  instead  of  em- 
ploying the  run  a^  a  source  of  light  to  form  the  prismatic  spec- 
trum we  make  use  of  the  red  light  which  is  produced  by  Nitrate 
of  S^rontia  dissolved  in  alcohol,  it  will  be  found  thaX  the  kind 
of  light  emitted  is  very  different  from  that  of  the  sun,  that  the 
greater  part  of  the  rays  arc  those  of  small  refrangibility,  and 
that  they  are  collected  at  the  lower  part  of  the  spectrum,  caus- 
ing the  point  of  maximum  intensity  for  light  to  i'all  within  the 
red  ray.  Just  FO  witli  rays  of  heat:  by  changing  the  source  of 
heat  we  obtain  different  k  nds  of  heat,  varying  in  refrangibility 
an  I  altering  the  po  ition  of  the  point  of  maximum  intensity  for 
heat  in  the  heat  spectrum,  in  proportion  as  thw  rays  of  one  de- 
gree of  refrangibility  preponderate  over  those  of  another.  This 
takes  place  according  to  a  certain  fixed  rule.  The  less  intense 
the  source,  the  lower  the  refrangibility  of  the  heat" radiated,  and 
the  nearer  to  the  red  end  of  the  spectrum  is  the  point  of  maxi- 
mum temperature.  The  more  intense  the  source  of  heat,  the 
more  abundant  the  emission  of  the  kinds  of  heat  posses  ed  of 
h'gh  refrang'bility.  Thus  the  sun,  the  most  inten  e  of  all  the 
sources  of  heat,  emits  the  more  refrangible  kinds  of  heat,  con- 
taining rays  which,  when  passed  through  a  prism,  undergo  pow- 

Describe  the  experiments  with  the  invisible  rays  obtained  from  the  electric  light  —94. 
Show  that  different  kinds  of  heat  are  emitted  by  different  sources.  How  does  tae  point 
of  maximum  intensity  for  beat  vary  with  the  source  ? 


THE    HEAT    OF    THE    ELECTRIC    LIGHT. 


71 


Fig.  26. 


erful  refraction,  and  are  distributed  over  the  whole  spectrum, 
extend'ng  as  high  even  as  the  extieme  violet.  The  nak;  d  flame 
of  a  lamp,  a  less  intense  source,  emits  rays  of  less  retVangibility, 
hardly  extending  above  the  blue  portion  of  the  spectrum.  Ig- 
nited platinum,  a  still  less  intense  source,  emits  those  kinds  of 
heat  which  have  a  still  'ower  retVangibility,  extending  not  much 
above  the  red.  Copper,  at  750°,  emits  those  of  even  a  still 
lower  degree  of  refrangibility,  while  from  hot  water,  at  212°, 
only  those  kinds  of  heat  are  emitted  which  are  posse-sed  of  the 
lowest  po>sib'e  refrangibility.  In  the  case  of  the  electric  light, 
which,  after  the  sun,  is  one  of  the  most  intense  sources  of  heat, 
the  proportion  of  the  more  refrangible  to  the  less  refrangible 
kinds  of  heat  is  shown  in  Fig.  26.  The  rays  extend  fioni  A 

to  E,  and  perpendiculars  erected 
at  various  points  represent  the 
calorific  intensity,  or  the  amount 
of  heat  of  that  particular  re- 
frangibility existing  at  tho-e 
points.  Then  the  ends  of  all 
^  the-e  perpendiculars  being  uni- 
ted, we  have  a  curve  whLh 
shows  at  a  glance  the  manner 
in  which  the  heat  is  distributed 
through  the  electric  spectrum. 
The  luminous  portion  of  the 
spectrum  is  unshaded,  the  non- 
luminous,  or  dark  portion,  is 
drawn  in  black.  It  will  be  ob- 
served that  while  this  Fource 
emits  kinds  of  heat  of  refrangi- 
bility equal  to  the  b'ue,  these 
are  small  in  quantity ;  that  the 
less  refrangible  kinds  are  larger 
in  amount  as  we  advance  from 
E  to  D,  where  the  luminous 
portion  of  the  spectrum  termi- 
nates :  that  lliese  still  further  in- 
crease in  quantity  as  advance  is 
made  below  the  red  into  the  in- 
visible portion  of  the  spectrum, 
and  finally  attain  their  greatest 


Curve  showing  the.  distribution  of  the.  heat 
in  the  spectrum  of  the  Eltctric  Light. 


What  is  the  relation  between  the  intensity  of  the  source  of  heat  and  the  refrangi- 
bility of  the  rays  J    Explain  Fig.  26. 


72  CALORIFIC    TINT. 

intensity  at  IT  ,  a  po'nt  considerably  below  the  red  end  of  the 
spectrum.  If  the  heat  spectrum  of  the  suii  were  drawn  on  the 
same  plan,  the  point  H  would  be  found  opposite  a  point  a  little 
above  D,  and  would  fall  within  the  light  or  illuminated  porficn 
of  the  spectrum,  instead  of  wholly  in  the  dark  or  invisible  por- 
tion. 

From  all  this,  it  seems  clear  that  as  there  are  different  kinds 
of  radiant  Light,  distinguished  by  a  difference  in  refrangibility, 
and  also  by  a  difference  in  color,  so  there  are  different  kinds  of 
radiant  Heat,  distinguish:  d  from  each  other  also,  by  a  difference 
in  refrangibility,  but  not  distinguished  from  each  other  by  color; 
and  that  different  sources  emit  these  different  kinds  of  heat  in. 
various  proportions. 

95.  Consequently  the  unequal  Diathermancy  of  the  same 
medium  for  Beat  proceeding-  from  different  sources  seems  to  be 
owing-  to  the  different  kinds  of  Heat  emitted  by  the  different 
sources.    This  being  so,  it  is  easy  to  see  that  the  reason  the 
rays  of  heat  proceeding  from  the  sun  can  traverse  glass  and 
experience  but  little  obstruction,  when  the  same  plate  of  gla>s 
can  hardly  be  traversed  at  all  by  heat  proceeding  from  a  com- 
mon fire,  a  lamp,  or  any  o;her  source  of  terrestrial  heat  is,  that 
the  rays  which  glass  transmits  are  tho  e  of  the  more  refrangible 
kinds  of  heat  alone,  and  it  is  these  which  are  the  most  abundant 
in  the  solar  beam ;     while  the  rays  of  heat  proceeding  from  the 
fire  are  those  of  the  less  refrangible  kinds,  and  these  glass  is  al- 
most entirely  incapable  of  transmitting  at  all ;  in  the  same  man- 
ner precisely  that  a  piece  of  blue  glass  will  transmit  perfectly  all 
the  rays  of  light  proceeding  from  a  Roman  candle,  while  it  will 
not  allow  any  of  the  rays  of  light  proceeding  from  a  flame  of 
a  green  or  red  color  to  pass  through  it  at  all. 

96.  The  unequal  Diathermancy  of  different  substances  for 
Heat  proceeding-  from  the  same  source  seems  to  be  owing  to  a 
property  in  bodies  in  relation  to  Heat,  analogous  to  the  prop- 
erty of  color  in  relation  to  Light,  and  called  Thermochrosis. 
The  o'her  peculiarity  brought  out  by  the  experiments  of  Mel- 
loni,  viz.,  that  heat  radiated  from  the  same  source,  and  therefore 
of  the  same  kind,  is  transmitted  completely  by  one  subs!ance, 
and  imperfectly  by  ano'her,  ^eems  to  be  owing  to  a  property  in 
bodies  for  h^at  exactly  analogous  to  the  property  of  color  in 
relation  to  light.     Thus,  92  out  of  every  100  of  the  rays  of 
heat  proceeding  from  an  oil  lamp  are  transmitted  by  a  piece  of 

95.  How  does  this  explain  the  transmission  of  heat  from  one  source,  and  non-trans- 
mis.- ion  of  heat  from  another  Fource.  by  the  same  medium  ? — 93.  Prove  that  there  is  in 
bodies  a  property  for  heat  analogous  to  the  property  of  color  for  light. 


THKRMOCUIIOSIS.  73 

Rock  Salt,  while  only  9  out  of  100  are  transmitted  by  a  piece 
of  ulum  of  equal  transparency  and  thickness.  The  reason  is, 
that  Rock  Salt  is  nearly  perfectly  transparent  to  heat,  while 
alum  acts  like  a  piece  of  colored  glass  upon  sunlight;  it  will 
stop  a  considerable  proportion  of  the  rays  and  allow  only  a  part 
of  them  to  pass  through.  Thus,  if  clear  glass  be  held  up  to 
the  sun  it  will  allow  all  the  seven  kinds  of  light  of  which  white 
light  is  composed  to  pass  through  it,  while  a  piece  of  blue  glass 
will  absorb  a  certain  portion  of  the  rays  and  only  allow  tho-e 
of  a  blue  color  to  pass  through  it.  This*  unequal  absorption  of 
light  of  different  kinds  is  the  cause  of  the  different  colors  of 
bodies,  and  this  absorption  is  effected  by  some  peculiar  property 
which  we  call  color ;  a  body  of  a  red  color  is  one  which  absorbs 
all  the  rays  of  light  except  those  which  are  red ;  of  a  blue,  all 
the  rays  except  the  blue,  &c.  In  like  manner  with  the  rays  of 
heat  proceeding  from  a  lamp,  Rock  Salt  will  allow  them  all  to 
pass  without  absorption,  and  they  all  go  through  unchanged, 
while  alum,  having  the  peculiar  property  of  absorbing  all  the 
rays  of  heat  except  those  of  a  particular  kind,  only  allows  the 
latter  to  pass  through.  This  peculiar  absorptive  property  for 
heat,  corresponding  with  color  for  light,  has  been  called  thermo- 
chrosis,  or  tint  for  heat. 

This  is  confirmed  by  another  point  of  agreement  between 
light  and  heat.  In  the  case  above  mentioned,  of  a  piece  of 
blue  glass  which  has  absorbed  all  the  rays  of  light  except  the 
blue,  and  allowed  these  alone  to  pass,  it  is  found  that  if  these 
blue  rays  be  allowed  to  fall  upon  a  second  piece  of  blue  glass 
they  undergo  no  further  absorption,  but  they  all  pass  through  it 
unchanged ;  the  reason  is,  because  all  the  rays  of  light  which 
the  second  piece  of  blue  glass  could  absorb  have  already  been 
absorbed  by  the  first  piece,  consequently  it  transmits  all  the 
light  which  has  reached  it  from  the  first  piece.  In  the  same 
manner,  if  the  rays  of  heat  which  have  succeeded  in  passing 
through  one  piece  of  alum  be  allowed  to  fall  upon  a  second 
piece,  they  will  undergo  no  absorption,  but  all  pass  through  un- 
changed, because  all  the  rays  of  heat  which  the  second  piece  of 
alum  could  absorb  have  already  been  absorbed  by  the  first 
piece ;  consequently  all  the  heat  which  reaches  the  second,  after 
having  passed  through  the  first  piece,  is  transmitted. 

Oa  the  other  hand  if,  instead  of  making  use  of  a  second  piece 

What  is  meant  by  the  calorific  tint  of  bodies?    What  light  does  this  throw  upon  the 
transmission  of  solar  heat  by  glass,  and  the  non-transmission  of  artificial  heat  1 


74  CALORKSCENCK. 

of  blue  glass,  we  make  use  of  a  piece  of  red  glass,  in  the  above 
mentioned  experiment  upon  light,  the  rays  of  light  which  have 
passed  through  the  blue  glass  will  not  pass  through  the  piece  of 
red  glass,  because  the  rays  which  red  can  absorb  have  not  been 
all  taken  out  of  it  by  the  blue ;  these  will  therefore  be  absorbed 
by  the  red,  and  the  result  will  be  that*  no  rays  of  light  whatever 
will  be  able  to  pass  through.  In  like  manner  with  the  rays  of 
heat  which  have  passed  through  the  first  piece  of  alum,  if  they 
be  allowed  to  fall  upon  a  piece  of  ice,  instead  of  a  second  piece 
of  alum,  as  before,  instead  of  passing  through  unchanged,  they 
will  all  be  absorbed,  because  the  calorific  tint  of  ice  is  not  such 
as  to  allow  them  to  pass. 

It  is  evident,  therefore,  that  bodies  possess  a  calorific  tint  for 
heat  precisely  analogous  to  their  colorific  tint  for  light.  The 
only  substance  which  seems  to  have  no  calorific  tint,  but  to  be 
perfectly  transparent  to  heat  of  all  kinds,  as  clear  glass  is  for 
light,  is  Rock  Salt.  In  all  experiments  upon  radiant  heat  this 
is  the  substance  that  should  bo  used  for  the  prisms  and  lenses 
which  are  required.  Its  diathermancy  is  so  perfect  that  the 
rays  of  heat  proceeding  from  the  human  hand  will  pass  through 
it  with  scarcely  any  absorption,  and  produce  a  perceptible  effect 
upon  the  thermo-multiplier. 

97.  The  refrangibility  of  rays  of  Heat  may  be  altered  by  re- 
radiation—  Calorescence.  When  heat  has  once  been  absorbed, 
whatever  may  have  been  its  original  source,  it  acts  in  all  cases 
in  the  same  manner  in  producing  expansion  ;  and  when  radiated 
again  it  does  not  necessarily  retain  the  peculiarities  of  the  source 
from  which  it  originally  proceeded,  but  its  refrangibility  depends 
entirely  upon  the  temperature  of  the  surface  which  emits  it  the 
second  time.  Hence  it  is  immaterial,  so  far  as  the  common 
effects  of  heat  are  concerned,  whether  it  were  originally  derived 
from  the  sun,  from  actual  flame,  from  ignited  platinum,  or  from 
a  non-luminous  body.  It  will  in  all  cases  be  much  affected  by 
the  nature  of  the  substance  from  which  it  is  re-radiated.  If 
the  temperature  of  the  second  radiating  substance  be  lower 
than  that  of  the  original  source,  the  refrangibility  of  the  rays 
of  heat  will  be  lessened,  and  on  transmission  through  a  prism, 
will  be  found  nearer  the  point  b ,  in  Fig.  25.  On  the  other 
hand,  if  the  temperature  of  the  second  radiating  substance  rise 

97.  Do  the  different  kinds  of  heat,  if  of  equal  intensity,  differ  in  their  effect  upon  the 
dimensions  of  bodies?  If  heat  be  absorbed  and  radiated  again  does  it  still  possess  the 
peculiarities  of  its  original  source?  Is  any  effect  produced  upon  the  refrangibility  of 
heat  by  re-radiution  ?  Explain  caloresceuce. 


DOUBLE    REFRACTION    OF    HEAT.  75 

higher  than  that  of  the  original  source,  the  ref -angib'lity  of  the 
rays  will  be  increased,  and  on  transmission  through  a  prism, 
wiil  be  found  nearer  the  point  R  ,  in  Fiy.  25.  Indeed,  their  re- 
frangibility may  be  so  much  increased  that  non-luminous  rays 
are  sometimes,  by  re-radiation,  rendered  luminous.  Thus  the 
combustion  of  oxygen  and  hydrogen  ga>es  produces  a  flame 
which  contains  only  rays  of  he  it  of  low  refrangibility,  and  con- 
sequently emitting  very  little  light;  but  on  introducing  a  cylin- 
der of  lime  into  the  flame,  the  refrangibility  of  the  rays  is  so 
greatly  increased  that  they  emit  light  too  intense  for  the  eye  to 
bea:%,  and  on  trail  ^mission  through  a  prism  the  point  of  maxi- 
mum intensity  for  heat  is  found  to  be  nearly  as  high  as  ?/  in  the 
colored  part  of  the  spectrum,  Fig.  25.  In  like  manner  the  rays 
of  S'dar  heat  are  possessed  of  high  refrangibility,  but  when  re- 
radiated  from  the  earth  their  refrangibility  is  very  much  less- 
ened, and  they  can  no  longer  pa>s  readily  through  the  air  and 
watery  vapor  which  they  previously  traversed  with  the- greatest 
ease.  This  alteration  in  the  refrangibility  of  heat  is  sometimes 
called  calorescence,  and  is  analogous  to  a  similar  alteration  in 
the  refrangibility  of  light,  treated  of  hereafter,  called  fluores- 
cence. 

£8  The  double  refraction  and  polarization  of  Heat.  It  is 
well  known  that  when  a  ray  of  light  falls  obliquely  upon  the 
surface  of  a  crystal  of  Iceland  spar  it  is  divided  into  two  dis- 
tinct rays  which  proceed  in  two  different  directions  through  the 
crystal.  One  is  in  the  same  plane  with  the  original  ray,  and  is 
called  the  ordinary  ray,  represented  at  o  ,  in  Fig.  27  ;  the  other 

is  not  in  the  same  plane  with  the 

-  27- original  ray,  and  is  called  the  ex- 

tiao/dinary  ray,  represented  at  E. 
In  like  manner,  if  a  rny  of  non- 
luminons  heat  from  the  lower  or 
red  end  of  the  solar  spectrum  be 
thrown  obliquely  upon  the  surface 
of  such  a  crystal,  it  will  be  found 
to  be  divided  al?o  into  two  rays, 
which  will  be  refracted  ac- 
^___Ka^m___^m_im  cording  to  the  same  law,  and  <>x- 
Refraction  of  iLat.  ""  SL'.'tiy  in  the  same  manner,  as  the 
rays  of  light.  The  two  rays  of 

9S    Explain  the  double  refraction  of  lisjht  and  heat.     What  is  meant  by  the  polariza- 
tion  of  tiie  doublj  rvtY;u-t<-d  r:i_,.s  ot  Ii0-'.u  iiiid  beat? 


76  POLARIZATION    OF    HEAT. 

light  produced  by  transmission  through  a  doubly  refracting  crys- 
tal are  found  to  have  received  a  peculiar  modification  called 
polarization,  the  effect  of  which  is  briefly  this:  —  A  mirror  placed 
in  an  inclined  position  at  a  certain  angle  above  or  below  either 
of  the  two  refracted  rays,  is  capable  of  reflecting  either  ray  in 
the  ordinary  manner  ;  but  if  placed  at  the  same  angle  of  incli- 
nation on  either  side  of  this  same  ray,  it  becomes  utterly  inca- 
pable of  reflecting  it.  The  other  ray  is  similarly  affected,  but 
the  position  of  the  reflecting  side  is  reversed.  In  like  manner, 
the  two  rays  into  which  a  single  beam  of  heat  is  divided  by  a 
doubly  refracting  crystal,  are  iound  to  po-sess  the  same  proper- 
ties of  polarization.  From  these  facts  it  appears  that  while 
there  are  many  points  of  close  analogy  between  Heat  and  Light, 
and  each  is  capable  of  conversion  into  the  other,  yet  as  one  may 
exist  without  the  other,  and  when  associated  together  one  may 
be  separated  from  the  other  without  any  diminution  of  the  in- 
tensity of  either,  they  are  consequently  in  all  probability  entirely 
distinct  agents,  or,  according  to  the  undulatory  theory,  are  the 
result  of  two  different  rates  of  vibration. 

99,  The  different  processes  through  which  Heat  may  pass 
in  seeking-  an  Equilibrium.  In  seeking  an  equilibrium  heat  may 
go  through  the  processes  of  conduction,  convection,  radiation,  ab- 
sorption, reflection,  transmission,  refraction,  double  refraction, 
and  polarization.  When,  however,  by  any  of  these  processes 
it  is  made  to  accumulate  in  any  substance,  it  always  produces 
certain  effects,  and  it  is  to  these  effects  thus  produced  by  heat 
that  we  next  turn  our  attention. 

Experiments  on  Diffusion  of  Heat. 

1.  Conduction.     To  show  that  sensation  is  no  test  of  temperature,  arrange  three 
bowls  containing  water  at  32°,  96°,  150°,  respectively      Dip  the  two  hands  into  the  first 
and  third  bowls,  and  then  at  the  same  instant  into  the  centre  bowl,  containing  water  at 
96°.    To  one  hand  it  will  fed  cold,  to  the  other  warm.     See  Fig.  2  . 

2.  To  show  that  heat  is  transferred  from  a  hot  body  to  one  that  is  colder,  introduce  a 
email  tin  cup  of  mercury  at  60°,  into  water  at  212°      A  thermometer  placed  in  the  cup 
will  soon  rise  to  212°,  and  the  mercury  will  become  uncomfortably  •warm  to  the  hand. 

3.  The  same  fact  is  shown  by  holding  a  rod  of  iron  in  the  flame  of  a  spirit  lamp. 

4.  That  different  substances  conduct  heat  with  different  degrees  of  facility  may  be 
shown  by  holding  with  one  hand  a  rod  of  m'ctul,  and  with  the  other  a  rod  of  glass,  in 
the  flame  of  the  same  spirit  lamp,  or  a  rod  of  brass  and  a  bit  of  charcoal.     The  charcoal 
may  be  inflamed  and  held  in  the  fingers,  not  more  than  \  of  an  inch  from  the  flame, 
without  any  uneasiness. 

5.  That  different  metals  conduct  heat  with  unequal  rapidity  may  be  shown  by  cones 
or  rods  of  different  metals  tipped  with  Phosphorus,  placed  upon  a  metallic  tray  at  equal 
distances  from  the  flame  of  a  lamp  below 

6.  The  difference  in  the  conducting  power  of  bodies  may  be  shown  by  surrounding 
three  canisters  of  tin,  of  the  saine  size,  with  cotton,  charcoal  powder,  and  iron  turning-*, 
contained  in  cylinders  of  pasteboard,  filling  the  canisters  with  hot  water  from  the  same 


99 
rium. 


State  the  different  processes  through  which  heat  may  pass  in  seeking  an  equilib- 


EXPERIMENTS   ON    CONDUCTION,  77 

ressel,  and  placing  a  thermometer  in  each ;  at  the  end  of  half  an  hour  they  will  have 
cooled  very  unequally. 

7.  Tnat  heat  progresses  from  particle  to  particle  may  be  shown  by  a  rod  of  iron,  one 
end  of  which  is  heated  iu  the  tiamv  of  a  lamp,  having  bits  of  paospaorus  priced  iu  order 
upon  it      They  inflame  successively.     See  /•'»!,'.  3. 

8.  vVrap  a  piece  of  linen  cloth,  or  of  writing  paper,  tightly  around  a  smooth  brass  or 
iron' knob,  and  hold  it  in  the  flume  of  a  spirit  lamp.     Tue  paper  will  Inflame  wita  diffi- 
culty in  consequence  of  the  rapid  conduction  of  tne  heat  by  tae  metal.     U'rap  tae  same 
substances  around  a  piece  of  wood,  and  note  how  much  more  rapid  tae  innammatioa  is 
in  consequence  of  the  poor  coaductiug  power  of  the  wood.     On  tais  principle  may  be 
explained  the  melting  of  a  bullet  of  lead  sinootnly  wrapped  in  a  bit  of  paper,  and  held 
over  a  lamp,  without  burning  the  paper. 

9.  The  imperfect  conducting  power  of  glass  may  be  shown  by  cracking  it  with  hot 
iron  ;  the  heat  of  the  iron  can  not  penetrate  into  the  glass ;  the  outside,  therefore,  only 
expands,  the  inside  retaining  its  original  dimensions,  and  the  two  are  torn  apart. 

10.  Prince  Rupert's  Drops.     Break  the  long  end. 

11.  The  imperfect  conducting  power  of  water  compared  with  metal,  may  be  shown  by 
pouring  water,  of  a  temperature  just  supportable  to  the  finger  into  a  tin  cup,  grasped  by 
.the  hand ;  it  immediately  becoaies  intolerably  hot,  owing  to  the  excellent  conducting 
power  of  the  metal. 

1 2.  The  poor  conducting  power  of  liquids  may  be  shown  by  placing  a  differential  ther- 
mometer at  t  ic  bottom  of  a  jar  filled  with  water  so  as  just  to  cover  very  sligatly  the  up- 
permost bulb  ;  pour  a  little  ether  on  the  water  and  inflame  it.     The  heat  Ls  intense,  but 
no  effect  whatever  is  produced  upon  the  thermometer,  though  a  very  slight  heat  applied 
to  the  bulb,  like  that  of  the  hand,  will  cause  the  thermometric  fluid  to  move  througu 
several  inches.    See  Fig  6. 

13.  The  poor  conducting  power  of  liquids  may  be  shown  by  freezing  a  little  water  at 
the  bottom  of  a  test  tube,  filling  the  tube  nearly  full  of  water,  and  holding  the  upper 
portion  m  an  inclined  position  over  a  spirit  lamp  ;  the  water  may  be  made  to  boil  with- 
out melting  the  ice:  see  Fig.  1.    The  ice  may  be  formed  by  introducing  the  tube  into  a 
freezing  mixture  composed  of  equal  parts  of  snow  and  salt. 

14.  The  same  fact  may  be  shown  by  pouring  into  a  similar  tube  a  small  quantity  of 
decoction  of  blue  cabbage,  then  filling  it  with  water  and  holding  it  in  an  inclined  posi- 
tion in  the  flame  of  a  spirit  lamp,  it  can  be  made  to  boil  on  tae  surface  without  disturb- 
ing the  blue  decoction  below  at  all. 

1  3.  Go  3V3C  tio  a.  To  show  that  liquids  must  be  heated  from  below,  bring  the  lower 
part  of  the  tube  used  in  the  preceding  experiment  over  the  spirit  lamp ;  the  blue  liquid 
will  immediately  begin  to  diffuse  itself  and  rise  to  the  surface,  in  consequence  of  its  par- 
ticles becoming  specifically  lighter  by  expansion. 

1 6.  To  prepare  the  decoction  of  blue  cabbage,  used  for  many  purposes  In  chemical 
experiments,  pour  boiling  water  on  purple  cabbage  cut  into  fine  pieces,  and  let  it  steep 
for  an  hour.     Strain  carefully  and  bottle,  with  a  little  strong  alcohol. 

17.  To  show  that  liq  lids  are  heated  by  convection,  fill  a  flask  with  strong  solution  of 
carbonate  of  potash  ;  tarow  in  some  bits  of  amber,  and  dilute  with  water  until  the  spe- 
cific gravity  of  the  solution  becomes  equal  to  that  of  the  amber.     Apply  the  heat  of  a 
spirit  lamp  below,  when  the  bits  of  amber  will  be  seen  to  rise  in  the  centre  of  the  vessel, 
and  descend  at  the  sides,  following  the  motion  of  the  water  in  which  they  are  suspended. 

1 8.  Heat  the  solution  of  carbonate  of  potash,  not  over  a  lamp,  but  by  dipping  it  in 
hot  water;  the  particles  of  amber  will  rise  at  the  sides  and  descend  at  the  centre;  as 
POO  a  as  it  arrives  at  the  same  temperature  with  the  surrounding  water  the  motion  ceases. 
Ta  ce  the  flask  from  the  water  and  the  current  is  reversed,  descending  upon  the  sides  and 
risi.ig  in  the  centre. 

1 9.  That  gises  conduct  heat  slowly  may  be  shown  by  filling  a  hollow  cubical  vessel  of 
met  il  with  boiling  water,  and  noting  the  coo'inp;  at  the  end  of  an  hour.     Fill  another  ves- 
sel of  the  s  tine  side,  made  of  metal  only  half  as  thick  as  the  first,  but  placed  within 
another  metallic  vessel  an  inch  larger  than  itself,  arranged  so  that  the  air  between  the 
two  can  not  escape,  making  a  cube  within  a  cube,  and  note  the  cooling  during  the  same 
time ;  it  will  be  much  less  in  the  last  than  in  the  first,  though  the  thickness  of  the  two 
vessels  in  the  last  case  is  just  equal  to  that  of  the  one  vessel  in  the  first. 

20  The  currents  produced  in  air  by  heat  may  be  shown  by  placing  a  small  wax  taper 
Under  a  tall  bell  glass ;  and  also  two  small  vessels  containing  ammonia  and  chlorohydric 
or  muriatic  acid  respectively.  A  cloud  is  produced  which  circulates  with  the  heated  ;iir. 

21.  Ridiation.     That  heat  leaps,  as  it  were,  from  hot  bodies  through  an  appreciable 
interval,  may  be  shown  bv  holding  a  thermometer  near  a  ball  of  metal  moderately  heated, 

22.  That  the  effect  diminishes  with  the  square  of  the  distance,  may  be  shown  by  ac- 
tual measurement,  one  thermometer  being  placed  at  the  distance  of  one  foot  from  the 
hot  body,  another  at  two  feet,  and  noting  the  effect. 

23.  That  the  escape  of  heat  from  a  body  by  radiation  varies  with  the  nature  of  tb.« 


78  RADIATION,  REFLECTION, 

surface,  may  be  shown  by  filling  three  canisters  of  thin  brass,  one  having  a  polished  sur- 
face, the  second  coated  with  lampblack,  aud  the  third  with  whiting,  witn  hot  water  from 
tae  same  vessel,  aucl  testing  the  temperature  at  the  end  of  an  hour.     The  first  will  be 
hottest,  the  second  the  coolest,  and  the  third  intermediate, 

2*.  The  same  tact  may  be  shown  by  placing  a  thermometer  at  an  equal  distance  from 
the  four  sides  Of  a  brass  cube  filled  with  foiling  water,  of  which  one  ride  is  SBbSS 
lahed,  the  second  has  tlie  natural  surface  of  the  brass,  the  third  fc  covered  with  a  coating 
Of  whiting,  and  the  tourtb  with  a  coating  of  lampblack  ;  the  polished  side  will  affect  the 
thermometer  the  least,  the  lampblack  tae  most,  &c. ;  the  bamlpuvced  near  the  four  sides 
successively  will  also  detect  the  difference  in  the  radiating  power 

2o.  Aosorption.  To  show  that  absorption  is  affected  by  the  nature  of  the  surface, 
and  is  proportional  to  the  radiating  power,  place  the  three  canisters  of  experiment  23 
filled  with  water  at  60o,  at  equal  distances  from  the  same  stove  ;  at  the  expiration  of  an 
hour  they  wiiA  be  of  very  different  temperatures,  the  blackened  canister  Sbg  £?WM£ 
est. 

26.  The  same  fact  may  be  shown  by  placing  three  thermometers,  one  having  its  bulb 
roughened  with  lampblack,  the  second  covered  with  whiting,  the  third  with  tTn  foil  at 
equal  distances  from  the  same  hot  ball.     The  blackened  thermometer  will  rise  the  high- 
est in  a  given  tune,  then  the  one  covered  with  whiting ;  the  one  covered  with  tin  foil  the 

ICtlSt. 

27.  To  show  the  effect  of  color  upon  the  absorption  of  solar  heat,  place  pieces  of  sheet 
copper,  two  inches  square,  colored  respectively  black,  brown,  blue,  green,  red.  yellow 
and  white,  upon  cakes  of  cerate  composed  of  equal  parts  of  beeswax  aud  olive  oil  melted 
together,  cut  a  little  less  than  two  inches  square  ;  expose  them  to  the  sun's  rays  and  note 
the  depth  to  which  the  cerate  ia  melted  under  each  piece, 

23.  The  same  fact  may  be  shown  by  exposing  different  thermometers,  having  their 
bulbs  differently  colorea,  to  the  sun's  rays,  or  by  using  thermometers  filled  with  differ- 
ently colored  alcohols.  In  equal  times  the  effect  in  both  cases  will  be  different. 

29.  To  show  that  there  is  a  difference  in  the  effect  of  color  upon  solar  and  terrestrial 
heat,  blacken  one  bulb  of  a  differential  thermometer,  cover  the  other  with  whiting,  and 
place  it  in  the  sun  ;  the  blackened  bulb  will  be  affected  the  most ;  place  the  same  instru- 
ment near  a  heated  ball,  and  no  such  result  will  take  place. 

30.  Reflection.    The  reflection  of  heat  may  be  shown  by  placing  a  hot  ball  and  a 
thermometer  on  opposite  sides  of  an  opaque  screen ;  the  latter  remains  unaffected.    Then 
hold  a  plate  of  tin.  or  a  common  looking  glass,  in  such  a  position  that  a  line  drawn  from 
the  ball  to  it  will  make  with  a  perpendicular  at  the  point  of  contact,  an  angle  equal  to 
(hat  formed  with  the  same  perpendicular  by  a  line  drawn  from  the  thermometer  to  the 
tin  at  the  first  point  of  contact ;  an  immediate  effect  will  be  produced  upon  the  ther- 
mometer, and  the  angle  of  incidence  will  be  equal  to  that  of  reflection .     Heat  is  there- 
fore reflected  like  light.     A  vessel  of  hot  water  may  be  used  instead  of  the  ball. 

31.  That  rays  of  heat  may  be  concentrated  by  parabolic  reflectors,  to  a  focus,  may  be 
shown  by  placing  a  cube  of  hot  water  in  front  of  a  parabolic  reflector,  and  a  thermome- 
ter in  its  focus,  and  interposing  a  email  screen  between  the  bulb  of  ths  thermometer  and 
the  cube.    The  mercury  will  immediately  begin  to  rise  in  consequence  of  the  reflection 
of  heat  from  the  mirror. 

32.  If,  instead  of  one  parabolic  reflector,  two  be  used,  a  thermometer  placed  in  the 
focus  of  one.  and  a  cube  of  hot  water  in  the  focus  of  the  other,  a  small  screen  being  in- 
terposed so  as  to  eut  off  all  direct  communication,  the  rays  of  heat  striking  the  first  mir- 
ror will  be  reflected  in  right  lines  to  the  second,  and  then  be  reflected  to  the  thermome- 
ter in  its  focus,  precisely  in  the  same  manner  as  light  would  be. 

33.  If  the  sides  of  the  cube  be  variously  coated  the  effect  upon  the  thermometer  will 
varv  with  the  surface  which  is  exposed  to  the  mirror,  showing  the  effect  of  surface  on 
radiation. 

34.  If  the  thermometer  be  made  with  a  cubical  bulb  of  metal,  and  its  four  sides  be 
differently  coated,  the  mercury  or  colored  fluid  in  the  stem  will  rise  to  different  heights, 
according  to  the  side  which  is  presented  to  the  mirror,  showing  the  effect  cf  surface  on 
absorption. 

35.  If  a  spermaceti  candle  be  placed  in  the  focus  of  the  mirror  the  effect  will  be  less 
than  when  an  alcohol  lamp  is  used,  thus  showing  that  the  amount  of  heat  emitted  by  a 
flame  is  not  in  proportion  to  the  light. 

36.  If  a  ball  of  iron,  heated  so  as  cot  to  be  quita  red  hot,  be  placed  in  the  focus  of  one 
mirror,  and  a  candle  tipped  with  phosphorus  and  chlorate  of  potash  in  the  focus  cf  the 
other,  the  candle  will  be  inflamed.    A  common,  match  may  be  lighted  in  the  same  man- 
ner, and  water  may  be  boiled. 

37.  To  show  that  all  bodies,  even  those  not  called  hot  bodies,  are  continually  radiating 
heat  to  those  colder  than  themselves,  place  a  thermometer  in  one  focus,  and  a  lump  of 
ice  in  the  other.    The  thermometer  will  radiate  more  heat  to  the  ice  than  is  radiated  to 
it  by  the  ice,  and  its  temperature  will  immediately  sink. 


AND    DIATHERMANCY.  79 

38.  To  Bhow  the  effect  Of  bright  surfaces  in  throwing  off  and  reflecting  rays  of  heat, 
coat  the  bulb  of  a  thermometer  with  tin  foil,  and  it  will  hardly  be  affected  at  all  by  the 
heat  from  a  hot  ball  when  held  near  it. 

3  9.  To  show  the  effect  of  transparent  screens  in  obstructing  the  passage  of  non-lumi- 
nous heat,  while  they  offer  no  impediment  to  that  of  solar  heat,  interpose  a  screen  of 
gliss  between  the  mirrors,  having  a  hot  ball  in  one  focus,  and  a  thermometer  in  the 
other,  and  the  heating  effect  will  be  at  once  cut  off.  Interpose  the  same  screen  between 
tiie  sun  and  a  thermometer  placed  in  the  focus  of  one  of  the  mirrors,  and  no  such  ob- 
struction will  take  place 

40.  The  same  fact  may  be  exemplified  by  holding  a  burning  glass  before  a  fire,  and  in 
the  rays  of  the  sun  j  the  glass  is  powerfully  heated  in  the  first  case,  but  not  at  all  in  the 
second. 

41.  Diathermancy.    To  show  that  diathermancy  is  not  proportioned  to  transpa- 
rency, employ  the  apparatus  represented  in  Fig,  22.    The  screens  of  glass  and  rock  salt 
need  not  be  more  than  three  or  four  inches  square,  and  may  be  set  into  blocks  of  wood. 
The  experiment  may  be  varied  by  using  an  air  thermometer  instead  of  the  bits  of  phos- 
phorus, and  observing  also  the  effect  upon  the  hands.     Instead  of  a  hot  ball,  a  flask  of 
boiling  water  may  be  used.     Pieces  of  glass  of  various  colors  may  be  employed  also,  in- 
stead of  the  transparent  glass. 

42.  for  these  experiments  a  delicate  air  thermometer  is  useful,  which  may  easily  be 
constructed  from  a  common  flat  bottomed  glass  flask,  by  pouring  in  alcohol  colored  red 
by  cochineal,  or  blue  by  litmus,  to  the  depth  of  an  inch,  and  then  inserting  a  tightly  fit- 
ting cork  through  which  passes  a  long  glass  tube,  a  yard  in  length  and  of  fine  bore,  fit- 
ting tightly  and  extending  to  the  bottom  of  the  flask  beneath  the  surface  of  the  liquid. 
On  blowing  through  the  tube  air  will  be  forced  into  the  flask,  and  the  fluid  will  rise  in 
the  stem      A  scale  of  wood  divided  into  equal  parts  may  be  attached  to  the  stem  by  wire. 
The  air  in  this  case  is  the  thermometric  fluid,  and  sucli  a  thermometer  will  indicate  very 
slight  differences  of  temperature  very  plainly  to  the  eye.     The  flask  may  be  coated  with 
limpblack  or  whiting  rubbed  in  a  mortar  with  spirits  of  turpentine,  and  when  no  longer 
wanted,  these  coats  may  be  washed  off  by  spirits  of  turpentine. 


MB  ft 


. 

§  II.— Effects  of  Heat:— Expansion. 

100.  Expansion  produced  by  Heat.  When  Heat  is  accumu- 
lated in  bodies  it  produces  very  powerful  effects.  In  general, 
it  causes  expansion,  and  alters  the  dimensions  of  bodies.  Heat 
is  antagonistic  to  Cohesion,  or  that  attraction  which  tends  to 
unite  the  particles  of  the  same  kind,  of  which  matter  is  com- 
posed ;  and  upon  the  balance  between  these  two  forces  depend  • 
the  dimensions  of  bodies,  and  their  state  as  solids,  liquids,  and 
ga^es.  At  ordinary  temperatures,  heat  and  cohesion  mutually 
balance  each  other,  in  all  solids;  but  if  temperature  be  increased, 
heat,  or  the  force  which  tends  to  push  the  particles  of  the  body 
apart,  becomes  stronger  than  cohesion,  or  the  force  which  tends 
to  bind  them  together;  and  the  dimensions  of  the  body  are 
therefore  necessarily  enlarged.  If  the  heat  be  increased,  th;j 
relative  strength  of  cohesion  is  still  further  diminished,  the 
particles  acquire  mobility,  and  a  liquid  is  produced.  If  it  be 

100.  What  is  the  first  effect  produced  by  heat  ?  To  what  force  is  heat  opposed  ?  How 
does  the  balance  between  these  forces  determine  the  state  of  matter?  \\hat  is  the 
cause  of  liquidity? 


80 


EXPANSION    OP   SOLIDS. 


still  farther  increased  the  liquid  becomes  a  gas.  The  first  effect 
of  heat,  therefore,  is  to  expand  all  bodies  into  which  it  enters, 
and  to  make  them  larger.  The  ratio  of  this  expansion,  how- 
ever, differs  greatly  in  different  substances.  Thus  with  the 
same  increment  of  heat,  liquids  expand  more  than  solids,  and 
aeriform  bodies  more  than  liquids.  There  is  also  a  considerable 
difference  in  the  expansibility  of  different  solids  and  different 
liquids ;  but  the  aeriform  fluids,  as  air  and  the  gases,  all  expand 
equally  with  the  same  increase  of  temperature. 

101.  Expansion  of  Solids.  The  expansion  of  a  solid  is  read- 
ily proved  by  fitting  a  piece  of  metal,  when  cold,  to  an  orifice 
or  notch,  and  then  putting  it  into  the  fire ;  as  temperature  rises 
it  will  steadily  increase  in  size,  and  soon  become  too  large  to 
enter  its  former  measure. 


Fig.  28. 


Fig.  29. 


Expansion  of  Solids. 


Ring  of  St.  Gravetande. 


The  piece  of  brass  attached  to  the  handle  in  Fig.  28,  is  ex- 
actly fitted  to  the  notch  in  the  plate,  so  as  readily  to  enter  it 
when  cold,  but  when  heated,  its  dimensions  are  so  enlarged  as 
to  render  this  impossible.  The  same  fact  may  also  be  shown 
by  the  rin^  of  St.  Gravesaiide,  in  Fig.  29,  where  the  ball,  a,  after 
being  heated,  becomes  too  large  to  pass  readily  through  the 
ring,  m,  which  formerly  admitted  of  its  easy  entrance. 

102.  The  Expansion  of  Solids  unequal.  Different  solids 
expand  unequally  for  equal  increments  of  Heat.  The  ratio 
of  expansion  may  readily  be  shown  by  an  instrument  called 


Of  the  aeriform  state?  How  does  the  expansion  of  liquids  and  gases  compare  with 
that  of  solids?— 101.  1  low  can  the  expansion  of  solids  be  proved.'  Describe  the  ring 
of  St.  Gravesaude.— 102.  Is  the  expansion  of  different  solids  equal,  or  unequal  ?  How 
can  it  be  proved  ? 


THE    PYROMETER. 


81 


the  Pyrometer,  one  form  of  which  is  represented  in  Fig.  30. 
A  metallic  rod,  A,  is  placed  upon  the  supports,  and  one  end 
fastened  firmly  by  the  screw,  B,  while  the  other  end  is  left  un- 
fasteir-d,  and  arranged  so  as  to  touch  the  short  arm  of  the  lever, 
K.  The  rod  is  then  heated  by  the  spirit  lamp,  and  its  gradual 
expansion  is  shown  by  the  motion  of  the  long  arm  of  the  lever 


ix.  30. 


Trie  Pyrometer. 

along  the  graduated  circle,  a  very  small  expansion  at  the  short 
arm  of  the  lever  causing  the  long  a:-m  to  traverse  an  arc  of 
considerable  size,  and  very  evident  to  the  eye.  In  comparing 
different  substances  by  means  of  this  instrument,  it  is  neces- 
sary that  all  the  rods  should  be  of  the  same  size  and  length, 
and  that  the  heat  of  the  lamp  should  be  applied  the  same  space 
of  time. 

From  experiments  made  with  the  pyrometer,  it  appears  that, 
in  most  instances,  there  is  a  relation  between  the  expansion  of 
the  metals  and  their  fusibility,  and  in  general,  that  those  which 
are  most  easily  fusible,  expand  most  with  equal  increments  of 
heat.  Thus  lead,  tin  and  zinc,  expand  much  more  from  the 
same  increase  of  heat  than  copper,  silver  and  iron,  and  the 
former  are  much  more  readily  fusible  than  the  latter. 

103.  Expansion  of  Metals.  Among  solids,  the  metals  ex- 
pand the  most ;  thus  lead,  in  being  heated  from  the  freezing  to 
the  boiling  point  of  water,  i.  e.,  from  32°  F.  to  212°,  expands 
much  more  than  glass,  earthen  ware,  and  porcelain.  The  met- 
als, however,  differ  very  much  among  themselves  in  expansi- 

Deseribe  fie  pyrometer. — 103.  Give  the  order  of  expansion  among  metals.  Is  the 
same  expansion  produced  by  equal  increments  of  heat  at  all  temperatures?  How  is  the 
total  expansion  of  a  body  calculated?  Do  bodies,  after  b«ing  heatud,  contract,  on  cool- 
lug,  to  their  original  dimensions  ? 

4* 


82 


EXPANSION    OF    METALS. 


bility  from  the  same  addition  of  heat,  as  will  be  seen  from  the 
following  table : 

Relative  Expansion  of  different  Solids. 


1000  parts  at  32o  F  , 

become  at  212°, 

or  are  lengthened. 

English  Flint  Glass,     . 
French  Glass  Tube, 
Platinum,   .         .         .  ' 
Steel, 

1000.811 
1000.801 
1000.884 
1001.079 
1001.083 
1001.182 
1001.392 
1001.466 
1001.718 
1001.801 
1001.909 
1001.937 
1002.848 
1002.942 

liii  1248  pa 
"    1148 
"    1131 
"      926 
"      923 
"      846 
"      718 
"      682 
582 
636 

;:  «« 

516 

;;   85i 

340 

rts. 

Antimony, 
Iron,        ~.         .         .         . 

Bismuth,     .         .         .         . 
GoM,       ... 

Copper,       .... 
Brass,      .... 
Silver,         .... 

Tin,         .... 
Lead,         .... 
Zinc,       .... 

The  expansion  of  the  more  permanent  solids  is  very  uniform 
within  certain  limits.  Thus  their  expansion  from  32°  to  122° 
is  equal  to  that  between  122°  and  212°,  but  above  212°  the 
expansion  proceeds  more  rapidly  as  the  temperature  rises,  and 
becomes  greater  for  equal  increments  of  heat.  Ten  degrees  of 
heat,  therefore,  added  to  any  solid  above  212°,  produce  a  greater 
expansive  effect  than  the  same  number  of  degrees  added  below 
212°.  The  total  increase  in  bulk  of  any  body  which  has  un- 
dergone expansion  from  heat  may  be  ascertained  by  trebling 
the  number  which  expresses  its  increase  in  length.  Nearly  all 
solids,  after  having  been  expanded  by  heat,  return  exactly  to 
their  original  dimensions  when  they  are  allowed  to  resume  their 
original  temperature.  Lead,  however,  constitutes  an  apparent 
exception ;  it  is  so  soft  that  the  particles  slide  over  each  other 
in  the  act  of  expansion,  and  do  not  return  to  their  former  posi- 
tion. A  lead  pipe  used  for  conveying  steam  permanently  length- 
ens several  inches  in  a  short  time,  and  the  leaden  lining  of  sinks 
and  gutters  is  soon  thrown  into  ridges  from  the  effect  of  the  hot 
water. 

104.  The  Force  of  Expansion.  The  expansion  of  metals 
by  heat,  and  their  subsequent  contraction,  are  often  employed 
with  great  advantage  in  the  Arts,  and  frequently  act  as  mo-t 
efficient  mechanical  powers.  The  amount  of  force  which  pro- 

104.  What  is  the  force  of  expansion  equal  to?    Give  illustrations. 


THE    FORCE    OF    EXPANSION.  83 


duces  these  expansions  and  contractions  is  enormous, 
equal  to  the  mechanical  power  required  to  stretch  or  compress 
the  solids  in  which  they  take  place  to  the  same  amount.  O  i 
heating  an  iron  sphere  of  12  J  inches  diameter,  from  32°  to  212°, 
its  expansion  exerts  a  force  of  60,000  Ibs,  upon  every  square 
inch  of  its  surface,  or  30,000,000  Ibs.  upon  the  whole  sphere. 
A  bar  of  iron  one  square  inch  in  section  is  stretched  Ttfiuff  °f 
its  length  by  a  ton  weight  ;  the  same  elongation  and  an  equal 
amount  of  force  is  exerted  by  increasing  its  temperature  16° 
F.  In  a  range  of  temperature  from  winter  to  summer  of  80° 
a  wrought  iron  bar  10  inches  long  will  vary  in  length  To5o7y 
of  an  inch,  and  will  exert  a  pressure,  if  its  two  ends  be  fastened, 
of  50  tons  upon  the  square  inch. 

105.  Illustrations.     The   immense  force  of  expansion   is 
clearly  proved  in  many  notable  instances.     Thus,  Southwark 
Bridge,  over  the  Thames,  is  constructed  of  iron,  and  surmounted 
by  stone,  and  the  arches  rise  and  fall  one  inch  within  the  usual 
range  of  atmospheric  temperature.     The  Hungerford  chain  sus- 
pension bridge  crosses  the  Thames  with  a  span  of  1352  feet  in 
length  ;  the  height  of  this  chain  road  way  varies  in  the  hottest 
day  in  summer,  and  the  coldest  in  winter,  to  the  extent  of  eight 
inches.     The  Menai  suspension  bridge  weighs  20,000  tons,  and 
this  is  raised  and  lowered  fourteen  inches  by  the  change  of  tem- 
perature between  winter  and  summer.     The  Britannia  Tubular 
bridge,  over  the  Menai  Straits,  expands  and  contracts  in  length 
from  one  to  six  inches  daily.     The  Victoria  bridge  at  Montreal, 
is  exposed  to  great  vicissitudes  of  heat  and  cold,  and  it  is  found 
that  beams  of  iron,  200  feet  in  length,  are  subject  to  .a  move- 
ment of  three  inches  in  the  climate  of  Canada.     The  Steeple 
of  Bow  Church,  in  London,  has  been  nearly  thrown  down  by 
the  expansion  of  rods  of  iron  built  into  the  mason  work.     Bun- 
ker Hill  Monument  is  sensibly  deflected  from  the  perpendicular 
by  the  influence  of  the  sun's  rays,  so  that  its  summit  describes 
an  irregular  ellipse. 

106.  The  Force  of  Contraction  Equal  to  that  of  Bspatisioi. 
The  force  of  contraction  is  equal  to  that  of  expansion,  and  quite 
as  irresistible.     Its  immense  power  was  strikingly  illustrated 
some  years  since  in  Paris.     The  two  sides  of  a  large  build- 
ing,   the    "  Conservatoire   des    Arts   et   Metiers"   having    been 
pressed  out  by  the  spreading  of  the  arched  ceilings  and  the  im- 
mense weights  supported  by  the  floors,  M.  Molard  undertook  to 

105.  Describe  noted  cases  of  expansion  produced  by  heat      Southwark  bridge.     Meiiai 
bridge.     Victoria  bridge,   &c.—  103.  To  what,  is  the  force  of  contraction  equal? 


84 


TIIE   FORCE    OF    CONTRACTION. 


remedy  the  evil  by  boring  holes  in  the  walls  at  the  base  of  the 
vaulted  ceilings,  and  opposite  to  each  other,  through  which 
strong  iron  rods  were  introduced,  so  as  to  cross  the  interior  of  the 
building  from  one  side  to  the  other.  On  the  projecting  ends  of 
the  bars  on  the  outside  of  the  building  were  placed  strong  iron 
plates,  which  were  screwed,  by  means  of  nuts,  tightly  against 
the  walls,  Fig.  31.  The  rods  were  then  heated  by  means  of 

Fig.  31. 


Restoration  of  a  Building  by  the  Force  of  Contraction. 

rows  of  lamps  placed  under  every  alternate  bar,  and  being 
lengthened  by  the  expansion,  the  nuts  and  plates  were  pushed 
out  to  the  distance  of  an  inch  or  more  beyond  the  walls.  While 
in  this  condition,  the  nuts  were  screwed  a  second  time  tightly 
against  the  wall.  The  lamps  were  then  extinguished,  and  the 
rods,  contracting  as  they  cooled,  drew  the  walls  together  with  a 

Describe  the  restoration  ef  the  building  at  Paris. 


APPLICATIONS    IN    THE    ARTS.  85 

force  almost  irresistible,  and  to  a  distance  as  great  as  that  to 
which  they  had  been  lengthened  by  expansion.  These  bars 
being  then  left  in  their  new  position,  the  alternate  bars,  which 
had  remained  unheated,  and  by  the  contraction  of  the  others 
had  b^en  also  made  to  project  beyond  the  walls,  were  again 
tightly  screwed  against  the  building.  These  were  in  turn  ex- 
panded and  lengthened  by  the  application  of  the  lighted  lamps, 
and  once  more  screwed  up  tightly  against  the  walls.  The 
lamps  were  then  extinguished,  and  by  the  contraction  of  the 
second  set  of  bars  the  walls  were  drawn  still  further  towards 
each  other.  These  wrere  then  left,  in  turn,  to  hold  the  building 
in  its  new  position,  and  the  first  set  of  bars  a  second  time  brought 
into  requisition.  And  thus  the  p:ocess  was  continued  until  the 
walls  were  drawn  into  their  proper  vertical  position  ;  and,  the 
bars  btjing  left  in  their  places,  they  have  remained  firm  and 
upright  ever  since.  In  this  manner  a  force  was  exerted  which 
th  i  power  of  man  could  scarcely  have  applied  by  any  other 
means.  The  same  process  has  since  been  applied  to  the  resto- 
ration of  other  buildings  which  were  threatening  to  fall. 

107.  Applications  in  the  Arts.  Advantage  is  taken  of  this 
force  of  contraction  in  many  of  the  Arts.  The  iron  tire  of 
wheels  is  always  made  somewhat  smaller  than  the  wheel.  It 
is  then  enlarged  by  being  heated  red  hot  and  placed  upon  the 
wheel  while  still  in  that  condition  ;  cold  water  is  then  thrown  on, 
contraction  ensues,  the  parts  of  the  wheel  are  bound  together 
with  great  firmness,  and  the  tire  so  tightly  fastened  in  its  place 
that  nothing  can  pull  it  off.  The  tire  of  the  wheels  of  locomotives 
is  put  on  in  the  same  way.  Tire  iron  hoops  of  casks  are  ap- 
plied when  hot.  The  great  vats  of  the  London  Breweries, 
some  of  which  are  large  enough  to  float  a  seventy-four  gun  ship, 
and  which  contain  liquid  enough  to  produce  a  freshet  if  they 
should  burst,  are  confined  by  enormous  iron  hoops,  weighing 
from  one  to  three  tons,  which  are  put  on  while  hot.  The  plates 
of  iron  or  copper  of  which  steam  boilers  are  made,  are  joined 

together  by  rivets  which 

Fig.  32.  are    inserted    and     ham- 

^  ^  me  red  clown  while  red  hot, 

'  re      tllUS 


Boiler  Plates  bound  together  by  Contraction.          Hindu    perfectly  Steam  mid 

water   tiht.     This   is   il- 


107.  State  some  of  the  applications  of  this  force  in  the  arts.     Explain  the  manner  in 
which  boiler  platu*  ar*  madw  steam-tight. 


86  INJURIOUS    EFFECTS    OF    EXPANSION. 

lustrated  in  F'KJ.  32.  The  strong  iron  -bands  used  in  the  manu- 
facture of  the  Parrott  and  Armstrong  guns  are  put  on  and  welded 
down  at  a  white  heat.  Moulds  for  casting  objects  in  metal  must 
be  made  larger  than  the  intended  size  of  the  object,  in  order  to 
allow  for  contraction  in  casting.  The  moulds  for  casting  can- 
non balls  must  always  be  made  larger  than  the  calibre  of  the 
guns,  011  account  of  the  contraction  and  shrinking  of  the  ball  in 
cooling ;  it'  of  the  same  size  as  the  bore,  the  balls  will  be  too 
small  for  the  gun. 

108.  Injurious  Effects  of  Expansion.    The  expansion  oc- 
casioned by  heat  often  produces  injurious  effects,  which  need  to 
be  guarded  against.      A  closely  fitting  iron  gate,  which  can 
readily  be  opened  on  a  cold  day,  is  held  tightly  in  its  place  on 
a  warm  day,  in  consequence  of  the  expansion  bo  h  of  the  gate 
and  the  fence.     The  pitch  of  a  piano  rises  with  the  diminution 
of  the  temperature,  in  consequence  of  the  contraction  of  the 
strings.     Clocks  go  faster  in  winter  than  in   summer.     Nails 
driven  into  mortar  get  loose  from  expanding  and  contracting 
more  than  the  mortar.     Not  unfrequently  carriage  wheels  are 
set  fast  in  con«equence  of  the  expansion  of  the  axles,  produced  by 
the  heat  of  friction ;  and  the  pistons  of  steam  engines  become 
bound  too  tightly  to  move,  when  exposed  to  excessive  heat. 
Metallic  roofs,  whatever  be  the  metal,  from  their  exposure  to  (he 
sun,  expand  and  contract  enormously,  and  must  be  constructed 
in  such  a  manner  as  to  admit  of  a  certain  amount  of  motion  be- 
tween the  various  parts.     The  shoes  of  horses,  if  nailed  on 
when  too  hot,  distort  the  foot  by  contracting  too  much  as  they 
cool.     The  iron  rails  of  railroads  will  be  thrown  from  position 
by  the  heat  of  the  sun  if  the  ends  are  permitted  to  touch. 
3,000  feet  of  rails  will  expand  nearly  3  feet  between  0°  and 
110°   Fahrenheit.     From  Liverpool  to  Manchester,  the  rails 
are  500  feet  longer  in  summer  than  in  winter. 

109.  Glass  often  Fractured  by  Expansion.     The  injurious 
effects  produced  by  expansion  are  particularly  apparent  in  the 
fracture  of  glass,  especially  if  thick,  upon  the  sudden  applica- 
tion of  heat.     The  outside  surface  is  expanded  by  the  action  of 
the  heat,  and  it  not  being  permitted  to  penetrate  the  inter'or  in 
consequence  of  the  poor  conducting  power  of  the  material,  the 
external    and    internal    portions    are    violently    torn    asunder. 


Why  must  moulds  for  casting  metallic  objects  be  made  larger  than  the  desired  size  ? 
108.  Mention  some  of  the  injurious  effects  of  expansion.  What  is  the  effect  upon  clocks  1 
Upon  railroads,  &c.  ?— 109.  Describe  the  effect  of  sudden  expansion  on  glass. 


THE    FRACTURE    OF    GLASS.  87 

When  glass  is  to  be  exposed  to  great  extremes  of  temperature, 
it  should  be  made  as  thin  as  possible,  and  in  all  cases  very 
gradually  heated.  When  hollow,  the  heat  should  be  applied  upon 
ths  inside  at  the  same  moment  as  upon  the  outside,  in  order  that  the 
one  surface  may  be  expanded  to  the  same  degree  with  the  other. 
This  is  the  reason  why  a  thick  glass  tumbler,  if  immersed  in 
hot  water,  will  escape  cracking,  if  the  hot  water  reaches  the 
inside  at  the  same  moment  with  the  outside.  Thick  glass  mir- 
rors are  liable  to  be  fractured  by  bright  gas  lights  placed  too 
near  them,  and  plate  electrical  machines  by  careless  heating 
with  a  lamp  in  order  to  dry  them. 

110.  Fracture  produced  by  Sudden  Cooling-.  On  the  same 
principle,  glass  that  has  been  expanded  by  the  action  of  a  pow- 
erful heat,  is  very  liable  to  crack  by  the  application  of  sudden 
cold.  'Hence,  the  glass  roofs  of  green-houses,  and  skyligh's, 
expanded  by  the  sun,  and  suddenly  contracted  externally  by 
cold  showers,  while  the  internal  portions  are  still  considerably 
expanded,  are  very  likely  to  be  cracked.  And  for  the  same 
reason,  any  glass  vessel,  filled  with  hot  liquid,  is  very  sure  to 
break  if  placed  upon  an  iron  nail  in  the  floor,  or  upon  any 
metallic  support.  Consequently,  neither  glass,  nor  any  other 
brittle  material  of  poor  conducting  ^o\ver  for  heat,  can  bear  to 
be  either  heated  or  cooled  suddenly.  For  this  reason  glass 
ware,  when  first  made,  being  nearly  or  quite  red  hot,  if  permit- 
ted to  remain  in  coM  air,  is  infallibly  shivered,  and  is  therefore 
always  cooled  gradually,  or  annealed,  by  being  carried  at  one  e 
to  a  long  hot  oven,  the  temperature  of  which  gradually  dimin- 
ishes from  the  front  to  the  rear,  through  which  it  is  slowly 
pushed,  until  quite  cold.  All  these  precautions  would  be  un- 
necessary if  glass  were  a  good  conductor  of  heat.  Advantage 
is  taken  of  this  property  in  the  manufacture  of  glass.  The 
gla^s-blowers  cut  out  patterns  in  glass  by  drawing  a  cold  iron 
over  it  when  in  a  heated  state ;  and  the  Chemist  shapes  and 
alters  his  flasks  and  bottles  by  drawing  over  the  cold  gla-s  a 
rod  of  heated  iron.  Watch  crystals  are  obtained  from  globes 
of  gla^s,  very  large  and  very  thin,  by  applying  to  the  surface 
heated  metallic  rings.  On  the  same  principle,  rocks,  which  are 
generally  poor  conductors  of  heat,  mny  be  split  by  building  a  fire 
along  (he  line  of  intended  f'ra  'ture,and  then  pouring  on  <  old  water. 
At  Seringapatam>  in  India,  roaks  eight  fret  in  thickness  and 
eighty  feet  in  length  have  been  detached  by  thi ;  simple  means. 

110.  Describe  the  effect  produced  on  glass  and  rocks  by  sudden  contraction. 


88 


RATE    OF    CLOCKS    ALTERED. 


111.  Metallic  Instruments  injured  by  Expansion.  Th<* 
metals  being  expanded  much  more 
for  a  given  increase  of  heat  than 
other  solids,  and  very  considerably 
altered  in  their  dimensions  by  slight 
variations  in  temperature,  delicate 
metallic  instruments  are  often  seri- 
ously deranged  by  this  means.  All 
measures  of  length  are  considerably 
lengthened  and  shortened  by  the 
heat  of  the  atmosphere. 

The  rate  of  going  of  clocks  is 
much  affected  by  changes  of  tem- 
perature. If  the  pendulum  be 
lengthened,  the  clock  goes  slower; 
if  it  be  shortened,  the  clock  goes 
faster.  If  the  bob  of  the  pendu- 
lum be  lowered  T  J^  part  of  an  inch, 
the  clock  will  lose  ten  seconds  in 
twenty-four  hours.  Now  it  has 
been  found  that  an  increase  of  tem- 
'perature  to  the  amount  of  30° 
F.,  will  lengthen  a  seconds  pen- 
dulum -jj-g  part  of  an  inch,  and 
cause  it  to  lose  eight  seconds  in 
twenty-four  hours.  Of  course  the 
clock  would  gain  eight  seconds 
daily,  if  the  temperature  should 
sink  30°  F.  This  continual  vari- 
ation in  the  movement  of  the 
clock  destroys  its  value  as  an  ac- 
curate measurer  of  time.  The  diffi- 
culty has  been  remedied  by  several 
contrivances. 

112.  Compensation  Pendulums.  In  the  gridiron  pendulum 
of  Harrison,  represented  in  Fig.  33,  the  bob  is  suspended  by 
a  rod  i,  from  the  lowest  of  the  three  upper  horizontal  ci  o^-bars. 
This  rod  passes  freely  through  holes  in  the  two  lower  cross-bars. 
The  cross-bar  of  suspension  is  supported  by  a  pair  of  ver.ical  rods 
of  brass,  a,  which  rest  upon  the  upper  of  the  lower  crass-bars. 


Gridiron  Pendulum. 


Ill    What  effect  is  produced  upon  the  rate  of  time  pieces,  and  upon  measures  of 
length  ?— 112.  Dwscribtt  1 1«  gridiron  pendulum  of  Harrison. 


COMPENSATION    PENDULUMS.  89 

This  cross-bar  depends  by  means  of  iron  rods,  e,  from  the  sec- 
ond of  the  upper  cross-bars,  which  in  turn  is  supported  by  ver- 
tical brass  rods,  c,  and  the^e  again  by  iron  rods,  d,  from  the 
upper  cross-bar,  which  is  directly  attached  to  the  point  of  sus- 
pension, b.  When  the  temperature  increases,  the  iron  rods  c?and 
e  expand  downwards,  while  at  the  same  time  the  brass  rods,  c 
and  a,  expand  upwards.  These  expansions  in  contrary  direc- 
Jions,  are  so  adjusted  as  to  counteract  each  other,  and  the  bob 
of  the  pendulum  is  thus  maintained  at  the  same  distance  from 
the  point  of  suspension.  The  process  is  reversed  when  the 
temperature  sinks.  This  pendulum  gained  the  reward  of  £20,- 
000  offered  by  the  British  Government  for  a  pendulum  that  did 
not  lo>e  more  than  a  fraction  of  a  second  in  a  year,  and  would 
enable  the  longitude  to  be  determined  within  thirty  miles. 

113.  The  second  mode  of  obviating  the  same  difficulty  is  by 
using  a  .hollow  cylinder  of  glass  for  the  bob  of  the  pendulum, 
and  filling  it  with  quicksilver.  As  the  rod  of  the  pendulum 
expands  downwards,  the  quicksilver  expands  upwards,  so  that 
the  centre  of  gravity  of  the  bob  is  maintained  at  the  fame  dis- 
tance from  the  point  of  suspension.  A  third  mode  consists  in 
using  compound  bars  of  metal  to  adjust  the  point  of  suspension. 
If  two  metals,  as  brass  and  iron,  one  of  wh'.ch  expands  much 
more  than  the  other,  be  firmly  united  throughout  their  whole 
length,  and  then  heated,  the  brass  expanding  more  than  the 
iron,  will  bend  the  bar  into  a  curve.  If  it  be  cooled  instead  of 
heated,  the  brass  contracting  more  than  the  iron,  will  bend  the 
compound  bar  in  the  opposite  direction.  This  is  represented  in 

Fig.  34 ;  the  lower  bar  rep- 
Fig-  34-  resents  the  compound  bar 
(the  brass  being  uppermost) 
in  the  state  in  which  it  is  at 
the  mean  average  tempera- 
ture;  the  second  line  repre- 
scnts  the  same  bar,  when 
heated  above  this  point ;  the  upper  line  represents  it  when 
coole:!  below  it. 

The  application  to  the  pendulum  is  represented  in  Fig.  So. 
The  point  of  o-cillat'on  is  formed  by  two  such  compound  bars, 
fastened  firmly  at  one  end,  and  at  the  o'her  extremity  left  free, 
and  nearly  touching  each  other,  o^y  leaving  room  for  the 
passage  of  the  delicate  spring,  by  which  the  pendulum  is  sus- 

113.  Describe  the  compound  bar.    The  compensation  pendulum. 


COMPENSATION 


pended,  At  tlie  moan  temperature,  tlie  compound  bars  are 
perfectly  straight,  as  represented  in  the  second  figure.  When 
the  temperature  rises,  the  pendulum  rod  is  lengthened,  and  the 
ball  lowered ;  but  at  the  same  time  the  compound  bar  is  bent 


te.  35. 


Compensation  Pendulum, 

downwards,  and  the  point  of  suspension  lowered  to  the  same 
amount,  so  that  the  distance  between  the  centre  of  the  ball 
and  the  point  of  oscillation,  is  the  same  as  before,  and  the  rate 
of  going  is  not  altered.  This  is  represented  in  the  figure  to 
the  left.  When  the  temperature  falls,  the  rod  is  shortened,  the 
ball  rises,  but  the  compound  bars  being  then  bent  upwards,  as 
is  seen  in  the  figure  to  the  right,  in  consequence  of  the  greater 
contraction  of  the  brass,  the  distance  between  the  point  of  oscil- 
lation and  the  ball  is  still  the  same,  and  the  rate  of  movement 
remains  unaltered, 

114,  Compensation  Balance.  The  compensation  balance 
wheels  of  watches  are  constructed  on  the  same  principle.  In 
warm  weather  the  diameter  of  the  ordinary  balance  is  length- 
ened, and  its  circumference  increased ;  in  cold  weather  it  is 
shortened,  and  its  circumference  diminished.  In  the  compen- 
sation balance,  Fig,  36,  the  rim  of  the  wheel  is  divided  into 
four  parts,  These  parts  are  made  of  compound  bars  of  dif- 
erent  metals,  the  most  expansible  being  outermost,  and  hav- 

114.  Describe  the  compensation  balance. 


EXPANSION    OF   LIQUIDS. 


91 


Compensation  Balance. 


ing  one  end  fastened  to  an  arm  of  the 
wheel.  Tho  other  end  is  loo--e,  and  has 
a  small  screw  attached  near  its  free  ex- 
tremity. When  the  temperature  rises 
ti.e  outer  metal  expanding  more  than 
the  inner,  curves  the  end  of  each  quad- 
rant more  towards  the  centre  and  so 
counteracts  the  general  expansion  of  the 
wheel.  The  reverse  takes  place  when 
the  temperature  sinks,  and  in  this  man- 
ner an  equal  motion  is  secured  at  all 
times.  This  is  an  application  of  immense  advantage  in  the 
construction  of  chronometers,  for  determining  the  longitude  at 
sea.  There  are  many  other  applications  of  the  same  principle, 
of  nearly  equal  value  to  Science  and  the  Arts, 

115.  The  Expansion  of  Liquids.  Liquids  expand  more  for 
a  given  increase  of  heat  than  Solids,  The  fact  of  expansion 
may  be  shown  by  dipping  a  common  thermometer  into  warm 
water,  or  by  heating  a  larger  tube  and  ball,  partially  filled  with 
water,  over  a  lamp :  Fiy.  ol.  If  the  liquid  be  colored  alcohol, 

Fig.  37. 


Expansion  of  Liquids. 

its  rise  in  the  tube  is  more  rapid  and  more  apparent  to  the  eye 
than  if  filled  with  water.  It  will  speedily  rise  from  c  to  <7, 
from  a  to  b.  This  expansion  takes  place  with  so  much  force 
that  all  closed  vessels  filled  with  liquids  burst  on  the  applica- 
tion of  heat. 

1 16.  Expansion  of  different  Liquids  unequal.  The  unequal 
expansion  of  different  liquids  for  an  equal  increase  of  temper- 
ature, may  be  shown  by  filling  two  bulbs  of  the  same  size,  to 
the  same  height,  with  different  liquids  and  dipping  them  into  the 
same  vessel  of  hot  water.  If  the  fluids  be  alcohol  and  water,  it 
will  be  found  that  the  alcohol  will  rise  in  the  tube  twice  as  high 


115.  How  does  the  expansion  of  liquids  compare  with  that  of  solids  1    How  can  the  ex- 
pansion of  liquids  be  proved  1 — 116.  llow  can  the  unequal  expansion  of  liquids  be  shown  1 


92 


EXPANSION    OF    GASES. 


"Unequal  Expansion  of  Liquids. 


as  the  water.  If  they  be  olive  oil 
and  water,  standing  at  the  same  level 
at  60°,  we  shall  find  that  when  the 
water  in  which  they  are  immersed 
boils,  and  they  have  been  raised  to 
212°,  the  one  has  expanded  much 
more-than  the  other ;  Fig.  38.  Alco- 
hol, on  being  heated  from  32°  to  212°, 
increases  in  bulk  ^  ;  olive  oil  ^g  ; 
water  ^T.  Twenty  gallons  of  alcohol 
measured  in  January,  will  become 
twenty-one  in  July. 

117.  The  Expansion  of  the  Li- 
quids produced  by  the  Condensation 
of  Gases.  By  compression,  combined 
with  great  reduction  of  temperature, 
several  of  the  aeriform,  or  gaseous 
forms  of  matter,  may  be  condensed 
into  liquids.  These  liquids  differ 
from  all  common  liquids  in  their 
enormous  expansion  on  the  applica- 
tion of  heat.  In  general,  the  air, 
and  other  gases,  expand  more  from  equal  increments  of  heat 
than  any  other  substances ;  but  these  peculiar  liquids  exceed 
them  in  this  respect,  and  are  the  most  expansible  substances 
known.  Thus  liquid  carbonic  acid,  in  being  heated  from  32° 
to  86°  F.,  expands  from  20  volumes  to  29,  which  is  more  than 
five  times  as  much  as  air.  Liquid  sulphurous  acid,  and  cyano- 
gen, expand  to  nearly  the  same  degree. 

118.  The  Expansion  of  Gases.  Aeriform  fluids  are  greatly 
expanded  by  heat,  and  much  more  than  either  solids  or  liquids 
for  the  same  increase  of  temperature.  With  equal  increments 
of  heat,  they  all  expand  equally,  If,  therefore,  the  ratio  of 
expansion  for  one  gas,  as  oxygen,  be  known,  then  the  ratio  lor 
common  air  and  for  all  the  other  gases  will  be  known  also. 
The  rate  of  expansion  for  all  gases  has  been  found  to  be  about 
T^  of  the  volume  which  the  gas  possessed  at  32°,  for  every 
degree  of  Fahrenheit's  thermometer.  This  calculation  is  based 
upon  the  experiments  of  Gay  Lussac,  who  found  that  1000 
cubic  inches  of  atmospheric  air,  raised  from  the  freezing  point, 

117  What  peculiarity  is  possessed  by  the  liquids  formed  by  the  condensed  gases  ? — 118. 
How  can  the  expansion  of  gases  be  shown?  What  is  the  rate  of  expansion  of  all  gase* 
for  one  degree  F.  ? 


EXPANSION    OF   AIR.  93 

32°  F.,  to  the  boiling  point,  212°,  Avere  expanded  so  as  to  make 
1375  cubic  inches.  It  follows,  therefore,  that  one  cubic  inch  of 
atmospheric  air  at  32°,  will,  if  raised  to  212°,  or  heated  by  180°, 
be  expanded  to  1.375  cubic  inches,  and  for  every  additional  180° 
of  temperature  it  will  receive  a  like  increase  of  volume.  The 
ratio  of  expansion  being  ¥J0-  for  1°,  if  any  volume  of  air  at  32° 
be  raised  to  the  temperature  of  32°-{-4900  =  5220,  it  will  expand 
to  twice  its  volume ;  and  if  it  be  raised  to  a  temperature  of 
32°-j-(2°X490°,):=10120,  it  will  be  expanded  to  three  times  its 
volume,  and  so  on.  Later  experiments  have  slightly  altered 
this  ratio,  and  show  that  the  different  gases  do  not  all  expand 
to  exactly  the  same  degree  for  equal  increments  of  heat ;  the 
inequality  may,  however,  be  disregarded  for  all  practical  pur- 
poses. In  general,  the  gases  and  vapors  all  dilute  equally  and 
to  the  same  degree  as  atmospheric  air. 

119.  Expansion  of  Air.    The  fact  of  the  expansion  of  air 
may  readily  be  shown  by  filling  an  India  Rubber  bag  with  air, 
clo-ing  it  tightly,  and  holding  it  near  the  fire.     As  the  air  ex- 
pands the  bag  will  become  more  and  more  tense,  and  finally 

burst  with  a  loud  report.  A 
more  elegant  experiment  is,  to 
take  a  glass  tube,  terminated  l;y 
a  bulb,  and  put  in  so  much  water 
as  to  about  half  fill  the  tube,  and 
then,  having  immersed  it  in  a  ves- 
sel of  water,  as  represented  in 
Fifj.  39,  apply  the  lieat  of  a  lamp 
to  the  bulb.  As  the  heat  rarefies 
the  air  in  the  bulb,  the  water  will 
be  forced  down  the  tube,  but  will 
Expansion  of  Air.  slowly  rise  again  to  its  former 

level  by  the  pressure  of  the  at- 
mosphere on  the  fluid,  when  the  lamp  is  removed,  and  the  air 
in  the  ball  allowed  to  contract. 

120.  The  expansion  of  Air  of  great  practical  utility.— The 
Draught  of  Chimneys.    The  great  increase  in  the  bulk  of  air, 
produced  by  heat,  diminishes  its  density  and  renders  it  specifi- 
cally lighter,  i.  e.,  lighter  than  an  equal  bulk  of  air  at  a  lower  tem- 
perature.    The  consequence  is  that  the  heated  air  being  thus 
made  less  dense  tends  to  rise,  just  as  a  cork  does  in  water,  or  a 

119    How  may  the  expansion  of  air  be  shown?— 120.  Why  is  the  expansion  of  air  of 
great  practical  iinportauce  ? 


DRAUGHT    OF    CHIMNEYS. 


balloon  in  the  air ;  this  creates  a  rush  of  air  from  every  side  to 
supply  its  place,  and  in  this  manner  powerful  currents  are  pro- 
duced, and  a  general  circulation  kept  up  in  the  atmosphere, 
which  is  of  the  greatest  practical  utility,  and  one  of  the  most 
beneficent  arrangements  in  Nature.  It  is  by  the  inequality  in  the 
weight  of  the  column  of  air  C  D,  within  the  chimney,  compared 
with  the  weight  of  a  column  of  cold  air  A  B,  on  the  outside,  of 
equal  base  and  height,  that  the  rush  of  cold  air  into  the  chimney 
from_below,  in  order  to  restore  the  equilibrium,  is  produced, 

which  creates  the  draught ;  Fig. 
40.  This  inequality  is  produced 
by  the  diminution  in  the  density 
of  heated  air  consequent  upon 
its  increase  in  bulk;  see  Fig. 
12.  It  is  upon  this  expansion 
produced  by  heat,  therefore,  that 
the  draught  of  chimneys  depends ; 
a  continued  stream  of  fresh  air 
is  supplied  to  the  fire,  and  the 
injurious  products  of  combustion 
are  removed,  and  without  it,  all 
processes  of  illumination  and 
combustion,  such  as  fires,  lamps, 
and  candles,  would  cease,  or  be 
maintained  only  by  a  cosily  and 
complicated  machinery.  Every 
six  tons  of  coal  consumed,  re- 
quires at  least  seventy-two  tons 
of  air  to  produce  perfect  com- 
bustion, i.  e.,  twelve  times  as  much  air  by  weight  is  required, 
as  coal.  Now  the  whole  of  this  quantity,  if  it  were  not  for  this 
extremely  curious  provision  of  Nature,  would  have  to  be  sup- 
plied artificially ;  and  it  can  readily  be  seen  what  a  check  this 
would  place  upon  many  of  the  arts  essential  to  the  comfort  of  man. 
Upon  the  same  diminution  in  density  depend  all  processes  of  ven- 
tilation, and  all  the  atmospheric  currents,  such  as  the  Trade 
wind>,  by  which  the  commerce  of  the  earth  is  wafted  on  its  way, 
and  the  land  and  sea  breezes,  by  which  the  heat  of  tropical  cli- 
mates is  mitigated.  At  the  equator,  the  hot  air,  rising  in  a 
steady  stream,  flows  off,  after  it  has  reached  a  certain  height  in 


The  Draught  of  Chimneys. 


Explain  the  currents  which  it  produces  in  the  atmosphere.  What  has  this  to  do  with 
ventilation?  The  burning  of  lamps,  and  fires?  Show  how  the  draught  of  chinineysia 
produced.  What  saving  does  this  effect  in  fuel  ? 


WATER    EXPANDS    FROM    COLD. 


95 


Fig.  41. 


the  atmosphere,  both  to  the  north  and  to  the  south,  and  this 
necessitates  a  steady,  current  near  the  surface  of  the  earth, 
from  the  north  >and  the  south,  towards  the  equator.  In  our  own 
climate,  in  summer,  the  hot  air  over  the  earth  rising  in  the  day 
time,  produces-  a  liow  of  cold  air  from  the  sea,  and  at  night  the 
process  being  reversed,  and  the  warm 
air  over  the  sea  rising,  produces  a  cur- 
rent of  cold  air  from  the  land.  In  this 
way  the  extremes  of  climate  are 
moderated,  and  the  heat  of  the  globe 
more  equally  distributed,  the  purity 
of  the  atmosphere  is  preserved,  and 
many  processes  absolutely  essential 
to  the  welfare  and  civilization  of  man 
proceed  with  undeviating  regularity. 
121.  Exception  to  tho  general 
law  of  Expansion  by  Heat.— Water 
at  certain  temperatures  contracts 
from  Heat,  and  expands  from  Cold. 
It  is  a  striking  fact,  and  a  most  con- 
clusive proof  of  design  in  the  consti- 
tution of  Nature,  that  water,  at  certain 
temperatures,  does  not  obey  the  usual 
law  of  expansion  from  heat,  and  con- 
traction from  cold.  Between  32°  and 
40°,  if  water  be  heated,  it  contracts  ; 
if  it  be  cooled,  it  expands.  If,  there- 
fore, water,  at  the  temperature  of  60°, 
be  cooled,  it  will  contract  until  it  reach- 
es 40° ;  and  then,  if  it  be  cooled  to  a 
lower  degree  than  this,  it  will  begin  to 
expand.  At  40°,  therefore,  water  is 
said  to  possess  its  maximum  density, 
because  if  it  be  heated  above,  or  cooled 
below  this  point,  it  becomes  less 
dense.  To  show  this,  fill  a  flask  with 
water  at  a  temperature  of  60°,  and 
adapt  to  it  a  cork,  through  which 

passes  a  glass  tube  of  small  bore,  Fig.  41,  and  a  thermometer. 
Insert  the  cork  and  tube,  and  fill  the  tube  with  water  to  the  height 

What  is  the  connection  between  the  expansion  of  the  air  and  land  and  sea  breezes? 
What  effect  has  this  on  climate  and  the  purity  of  the  air  ?— 121.  Describe  the  exception 
presented  by  water  to  the  general  law  of  expansion  by  heat  At  what  temperature 
does  water  begin  to  expand  by  cold  ?  liow  cau  this  be  proved  ?  Describe  Fig  41. 


Expansion  of  Water  >n  cool- 
ing from  40°  to  32°. 


96  IMPORTANCE    OF    THIS    PECULIARITY. 

of  two  or  three  inches  above  the  flask.  Then  immerse  the  flask 
in  a  freezing  mixture  of  salt  and  ice  at  0°.  The  water  will  im- 
mediately begin  to  contract  and  sink  in  the  tube.  But  presently 
this  will  cease,  and  it  will  begin  to  rise  again,  showing  expansion. 
The  volume  of  the  water  has,  therefore,  first  been* diminished  by 
the  reduction  of  temperature,  and  then,  secondly,  increased.  The 
thermometer  shows  that  this  increase  begins  to  take  place  at  40°, 
and  by  the  time  its  temperature  has  sunk  to  32°,  the  water  will 
have  risen  in  the  tube  a  considerable  distance  above  its  original 
position,  and  acquired  the  same  bulk  as  it  would  have  done  if 
heated  to  48°,  so  that  it  expands  just  as  much  in  cooling  8°  be- 
low 40°,  as  it  does  in  being  heated  8°  above  that  point.  It  has 
been  ascertained  by  experiment  that  the  expansion  of  water 
continues  even  below  32°,  for  if  kept  perfectly  quiet  and  undis- 
turbed, water  may  be  cooled  as  low  as  12°  without  freezing, 
and  it  was  expanded  as  much  in  some  of  the  experiments  by 
cooling,  as  it  would  have  been,  if  heated  to  75°. 

122.  Important  results  of  this  exception  to  a  general  Law 
of  Nature.  The  most  important  effects  result  from  this  remark- 
able peculiarity  of  water.  If  water  became  steadily  heavier  as 
it  cooled,  and  its  density  continued  to  increase  until  it  froze,  as 
is  the  case  with  mercury,  ice  would  be  heavier  than  water,  and 
as  soon  as  formed,  would  subside  to  the  bottom  in  successive 
portions,  until  the  whole  of  the  water,  however  deep,  had  be- 
come solid.  It  is  quite  evident,  that  under  these  circumstances, 
in  the  autumn,  and  early  winter,  the  water  of  lakes  and  rivers 
gradually  imparting  its  heat  to  the  atmosphere,  would  soon 
reach  a  uniform  temperature  of  32°  throughout  the  whole  mass, 
be  converted  into  one  solid  body  of  ice,  and  occupy  a  very  long 
time  in  resuming  the  liquid  form  in  the  spring.  According  to 
the  present  arrangement  the  instant  that  any  portion  becomes 
colder  than  40°,  in  consequence  of  the  diminution  of  its  specific 
gravity  by  expansion,  it  rises  to  the  top  and  collects  upon  the 
surface;  and  as  water  parts  with  ite  heat  very  slowly,  for 
reasons  hereafter  to  be  explained,  the  upper  portions  may  sink 
as  low  as  32°,  while  the  great  mass  below  is  at  the  tempera- 
ture of  40°.  Consequently,  during  the  whole  of  a  long  winter, 
while  the  upper  portions  of  water  are  at  32°,  or  actually  frozen, 
the  lower  rarely  sink  below  40°,  and  the  greater  part  escapes  solidi- 
fication altogether.  At  the  instant  of  freezing,  a  great  additional 
expansion  takes  place,  in  consequence  of  which  the  specific  gravity 

122.  What  important  consequences  result  from  this  peculiar  constitution  of  water  ? 


PROVED    BY    EXPERIMENT. 


97 


of  ice  becomes  considerably  less  than  that  of  the  cold  water  at 
32°,  from  which  it  is  formed,  and  it  floats  upon  the  surface  ;  thus 
the  ice  is  kept  where  it  can  be  most  readily  reached  by  the 
sun's  rays,  and  the  process  of  melting  in  the  spring  be  easily 
accomplished.  In  general,  therefore,  however  cold  the  weather, 
and  however  thick  the  ice  which  is  formed,  the  great  body  of 
water  never  sinks  below  the  temperature  of  40°,  too  high  to 
freeze,  and  thus  the  greater  part  of  the  water  of  seas  and  riv- 
ers even  in  the  Arctic  zone  escapes  solidification. 

123.  This  peculiar  constitution  of  Water  proved  by  ex- 
periment. This  peculiar  constitution  of  water  can  be  readily 
shown  by  a  very  simple  experiment,  Fig.  42.  Let  the  tall  glass 


Warm  Water  Collecting  at  Bottom  of  Lakes  in  Winter. 

vessel,  1,  be  pierced  so  as  to  admit  of  the  insertion  of  two  ther- 
mometers, one  near  the  top,  the  other  near  the  bottom.  Just 
beneath  the  upper  thermometer  a  brass  cup  is  fitted  around  the 
glass  vessel,  and  filled  with  broken  ice  at  the  temperature  of 
32°.  Water  at  GO0  is  then  poured  into  the  glass  jar,  and  both 
thermometers  of  course  stand  at  the  same  point,  viz.,  CO0.  The 
effect  of  the  melting  ice  is,  to  cool  the  water  in  the  upper  part 
of  the  vessel,  and  its  density  being  thereby  increased,  it  sinks 
to  the  bottom,  while  the  wrarm  water  collects  at  the  top.  At 
the  expiration  of  a  few  moments  the  apparatus  will  be  in  the  con- 
dition indicated  in  vessel  2 ;  the  lower  thermometer  will  have  sunk 
to  45°,  the  upper  one  will  be  at  50°  or  55°.  This  process  will 
go  on  until  the  lower  thermometer  has  sunk  to  40°  F.  The 

123    How  can  the  collection  of  warm  water  at  the  bottom  of  lakes  be  proved?     Do- 
scribe  the  exp«'"iment  with  tue  three  jars. 

5 


WATER    EXPANDS    IN    FREEZING. 


upper  thermometer  will  then  b"gin  to  sink,  and  soon  stand  also 
at  40°.  Instead  of  remaining  stationary,  however,  at  this  point, 
it  will  descend  until  it  reaches  32°,  and  at  the  end  of  half  an  hour 
the  apparatus  will  be  in  the  condition  indicated  in  vessel  3,  i.  e., 
the  warmer  water  of  40°  will  be  at  the  bottom,  the  colder  water 
of  32°  will  be  at  the  top.  This  represents  the  condition  of  a. 
lake  in  winter,  cooled  by  the  contact  of  the  cold  atmosphere  on 
its  upper  surface,  and  it  is  explained  on  the  principle  mentioned 
above. 

124.  Water  expands  in  freezing1.  At  the  moment  of  con- 
gelation Avater  also  undergoes  a  still  farther  expansion ;  and 
this  takes  place  with  irresistible  power,  so  that  the  vessels  in 
which  it  is  confined,  if  they  be  full,  are  infallibly  broken.  This 
i  j  the  cause  of  the  bursting  of  water  pipes  at  the  approach  of 
winter.  This  expansion  is  supposed  to  be  due  to  the  crystalli- 
zation of  the  water  as  it  freezes,  and  to  the  fact  that  the 
crystals  which  are  formed  do  not  lie  side  by  side,  closely 
packed  together,  but  cross  each  other  at  angles  of  60°  and 
1 .0°,  thus  leaving  large  interstices.  The  water,  therefore,  neces- 
sarily occupies  more  space  than  it  did  before.  The  expansion  of 
water  in  cooling  and  freezing  is  well  shown  in  Fig.  43.  A  glass 
flask  is  filled  with  water,  and  a  cork  insert- 
ed, through  which  passes  a  tube,  open  at 
both  ends.  The  water  rises  into  this  tube 
some  distance,  and  this  po:nt  is  marked 
upon  the  scale.  A  thermometer  is  aho 
passed  through  the  cork  for  the  purpose  of 
indicating  the  temperature  of  the  water. 
The  whole  apparatus  is  then  immersed  in  a 
jar  containing  a  mixture  of  ice  and  salt, 
at  temperature  of  0°.  The  first  effect  is 
the  rising  of  the  water  in  the  tube,  pro- 
duced by  the  contraction  of  the  glass  flask 
in  consequence  of  the  cold  of  the  mixture. 
This,  however,  is  only  momentary.  The 
next  effect  is  the  rapid  falling  of  the  water 
in  the  tube,  which  goes  on  until  the  ther- 
mometer sinks  to  40°.  It  then  begins  to 
rise  steadly,  and  continues  to  do  so  until 
congelation  takes  place,  when  there  is  a 
sudden  and  very  great  expansion,  and  the  flask  is  generally 


Fig.  43. 


Zero 


Expansion  nf  Water  in 
Freezing. 


124.  What  effect  has  freezing  upon  the  bulk  of  water?    Describe  Fig.  43     Show  thu 
grea.o  foi-ce  with  which  this  expansion  takes  place. 


'  ILLUSTRATIONS.  9^ 

broken.  The  force  with  which  this  expansion  takes  place  h 
very  great,  and  cannon  filled  with  water  and  plugged,  at  the 
muzzle,  may  readily  be  buivt.  In  1784-5  Major  AVilliams,  at 
Qiiebec,  made  -some  experiments  upon  this  subject,  i:v  one  of 
which  an  iron  ping  three  pounds  in  we'ght,  was  projected  f.om 
a  bomb-shell  to  the  distance  of  415  feet,  and  shells.  o;ie  and  a 
half,  and  two  inches  in  thickness  were  bur^t,by  tho  freezing  of, 
the  water.  The  Florentine  Academicians  burst  a  hollow  brass 
g'obe,  having  a  cavity  of  only  an  inch,  by  freezing  the  water 
with  which  it  was  filled  ;  and  it  has  bc-en  estimated  that  the  ex- 
pan  ive  power  in  this  case  was  equal  to  27,720  pound-. 

125.  Illustrations.— Mountains  broken  down.  It  is  this 
expansion  of  water  in  congealing  that  makes  the  freezing  of 
vegetables  and  fruits,  in  the  early  winter,  de .- tnictive  to  their 
organization.  The  fanner  makes  use  of  this  force  to  break  up 
the  land,  by  heaping  it  in  ridges  in  the  autumn,  and  exposing,  there- 
fore, a  large  surface  to  the  action  of  the  frost.  The  water,  in 
freezing,  separates  the  particles  of  the  soil,  and  when  melting 
takes  place  in  the  spring,  the  whole  settles  down  into  a  fine  and 
comparatively  dry  powder,  very  favorable  to  early  vegetation. 
Nature  m  ikes  use  of  this  force  upon  a  large  scale,  to  break 
down  and  grind  up  in  o  fragments  the  cliffs  and  mountains,  and 
thus  to  modify  very  materially  the  face  of  the  earth.  The 
water  running  into  cracks  and  fis  ures  in  the  rocks,  freezes  in 
the  winter,  and  by  its  expansion  breaks  off  large  masses,  which 
for  the  time  are  held  in  their  places  by  the  strong  cohesive 
power  of  the  ice;  but  on  the  approach  of  spiing  this  melts,  and 
the  mass  is  precipitated  into  the  valley  below.  In  the  same 
manner,  vast  masses  of  earth  are  loosened  from  the  smooth  sur- 
faces of  mountains,  and  slid u  down,  in  the  spring,  into  the  val- 
leys. Hardly  any  other  agency  in  nature  has  so  much  effect 
as  this  in  altering  the  face  of  the  earth.  This  force  also  ope- 
rates powerfully  in  overthrowing  anrl  deranging  the  works  of 
man.  Railroads  are  thrown  out  of  level  by  the  expansion  of 
the  frozen  ground  beneath  them ;  fences  are  raised  out  of  line ; 
buildings  are  elevated  in  the  air;  the  wal's  of  cellars  are  driven 
inwards.  The-e  effects  are  especially  exhibited  in  stiff  c'ay 
soils,  on  account  of  the  adhesiveness  of  the  clay,  and  the  great, 
amount  of  water  which  it  conta'ns.  The  posts  of  fences  raised 
from  their  beds  by  the  expansion  of  the  fro 4,  do  not  return  to 
it  when  this  frost  melts  in  the  spring,  and  the  fence  is  perma- 

125.  Give  illustrations  of  the  operation  of  this  force  in  Nature. 


100 


THE    THERMOMETER. 


nsntly  deranged.  A  single  stone  projecting  into  the  clay  on  the 
outside  of  the  cellar  of  a  building,  if  within  reach  of  the  frost, 
will  give  to  the  heaving  earth  a  lever  by  which  the  heaviest 
building  may  be  raised  from  its  foundation.  For  the  same 
reason  banks  of  clay  thrown  up  against  the  underpinning  of 
houses  are  very  apt  to  push  them  in  and  undermine  the  build- 
ing. 

126.  Other  substances  beside  water  expand  as  they  solidi- 
fy. Water  is  not  the  only  liquid  which  expands  as  it  solidifies. 
The  same  effect  has  been  observed  in  a  few  others,  which  as- 
sume a  highly  crystalline  structure  on  becoming  solid.  Melted 
antimony,  bismuth,  iron  and  zinc,  are  examples  of  it.  Mercury 
is  a  remarkable  instance  of  the  reverse,  for  when  it  freezes  it 
suffers  a  very  great  contraction.  It  is  on  account  of  this  prop- 
erty that  fine  castings  can  be  made  from  iron.  The  metal,  as  it 
cools  and  solidifies,  expands  so  as  to  be  forced  into  the  most 
delicate  lines  of  the  mould.  Antimony  possesses  this  property 
in  a  high  degree,  and  for  this  reason  is  mixed  with  tin  and  lead 
to  form  type  metal  and  give  the  mixture  the  property  of  ex- 
panding into  the  moulds  in  which  the  types  are  cast.  It  is 
because  gold  and  silver  do  not  pos  ess  this  property,  but  on  the 
contrary  shrink  greatly  as  they  cool  in  moulds, 
that  coins  can  not  be  made  by  casting,  but  re- 
quire to  be  stamped. 

127.  Expansion  used  as  a  measure  of 
Temperature.— The  Thermometer.  One  of 
the  most  interesting  applications  of  the  law  of 
expansion  by  heat,  and  contraction  by  cold,  is 
the  thermometer.  This  is  an  instrument  in- 
tended to  indicate  and  to  measure  changes  in 
temperature,  and  has  received  its  name  from 
two  Greek  words  signifying  the  measure  of 
heat — 6eQfi.bg  and  [t^oov.  It  is  founded  on 
the  principle  that  the  expansion  of  matter  is 
proportional  to  the  augmentation  of  temper- 
ature, and  -is  designed  to  measure  the  varia- 
tions of  heat  and  cold.  The  first  attempt  to 
measure  such  variations  on  this  principle  was 
made  by  Sanctorius,  an  Italian  physician,  in 
the  seventeenth  century.  As  originally  con- 

126.  What  other  substances  besides  water  expand  as  they  solidify  ?  What  practical 
applications  are  made  of  this  in  the  casting  of  n  etuis?— 127.  What  is  the  thermometer? 
What  is  the  principle  on  which  it  depends  ?  Wlio  invented  the  instrument  ?  Describe 
the  first  form  of  it. 


Fig.  44. 


Thermometer  of 
Sanctorius. 


THE    AIR    THERMOMETER. 


101 


45- 


structed  it  was  a  rude  instrument,  and  it  has  reached  its  present 
stale  of  perfection  only  by  degrees,  anJ  after  sn;:ces  ive  improve- 
ments by  some  of  the  most  distinguished  philosophers.  These 
labors  have  been  directed  towards  the  improvement  of  i!s  form, 
the  selection  of  a  good  thermometric  fluid,  and  the  arrangement 
of  the  scales,  by  which  the  rise  and  fall  of  this  fluid  are  indi- 
cated. The  thermometer  of  Sanctorius  is  represented  in  Fig. 
44.  He  employed  a  glass  tube  blown  into  a  ball  at  one  extrem- 
ity, and  open  at  the  other.  After 
expelling  a  small  part  of  the  air  by 
h  'ating  the  ball,  the  open  end  was 
plunged  into  a  vessel  of  colored  li- 
quid, and  as  the  air  in  the  ball  cooled, 
this  colored  liquid  ascended  the  tube. 
Any  variation  of  temperature,  by  ex- 
panding or  contracting  the  air  in  the 
ball,  would  then  cause  the  liquid  in 
the  tube  to  rise  or  fall,  thus  forming 
an  imperfect  air  thermometer. 

128.  Air  Thermometer.  A  bet- 
ter construction  for  an  air  thermome- 
ter is  represented  in  Fig.  45.  It 
consists  of  a  glass  flask,  with  a  bot- 
tom flattened  so  as  to  stand  firmly 
upright,  containing  a  small  quantity 
of  alcohol,  tinged  red  by  cochineal, 
and  stopped  closely  by  a  cork,  or  by 
a  stopper  of  brass,  screwed  tightly  to 
a  ring  of  the  same  metal  cemented  to 
the  neck  of  the  flask.  Through  this 
stopper  is  passed  a  tube  of  one-eighth 
inch  bore,  and  a  yard  in  length,  open 
at  both  ends,  This  tube  is  cemented 
tightly  into  the  stopper,  and  dips  into 
the  liquid.  A  scale  of  wood  or  metal, 
divided  into  equal  parts,  is  attached 
to  the  tube  by  fine  wire.  There  is, 
therefore,  a  quantity  of  air  confined 
within  the  flask  which  can  not  escape, 
and  when  this  expands  by  the  ap- 


Air  Tuermomtter. 


128    Describe  a  second  form  of  the  ai? 
thermometers? 


What  are  the  defects  of  such. 


to? 


THE    DIFFERENTIAL    THERMOMETER. 


plication  of  heat,  the  colored  alcohol  is  forced  up  the  hihe. 
Thus  the  height  of  the  fluid  will  ind  cate  the  expansion  of  the 
air,  and  consequently,  the  degree  of  heat  to  which  the  instru- 
ment i?  exposed.  There  are,  however,  two  objections  to  the 
employment  of  air  for  this  purpose.  Its  expansions  and  con- 
tractions are  so  great,  even  from  small  changes  of  tempera!  ure. 
that  a  tube  several  feet  in  length  would  be  required  to  measure 
them ;  and  as  the  tube  is  necessarily  open  to  the  air,  the  con- 
t'nuai  variation  in  the  pressure  of  the  atmosphere  elevates,  and 
depresses  the  colored  liquid  without  any  reference  to  the  varia- 
tions in  temperature ;  and  thus  the  instrument  is  converted  into 
a  rude  barometer,  and  made  a  measure  of  the  pressure  of  the 
atmo-phcre,  as  well  as  of  temperature.  It  is,  however,  an  ex- 
ce  'dingly  useful  instrument  in  the  laboratory  for  experiments 
on  hi  at,  to  detect  on  the  spot  and  make  plainly  manifest  to  the 
eye,  sudden  variations  in  temperature  and  small  degrees  of  heat. 
129.  The  Differential  Thermometer.  For  the  above  rea- 
sons the  air  thermometer,  for  common  purposes,  is  both  incon- 
venient and  inaccurate,  and  therefore  has  long  since  been  laid 
aside.  There  is,  however,  a  modification  of  this  instrument, 
invented  by  Mr.  Leslie,  and  called  tire  differential  thermometer, 
which,  for  certain  purposes,  is  a  very  elegant  and  useful  instru- 
ment, A  drawing  of  this  instrument  is  represented  in  Fig-  46, 
and  it  is  designed,  as  its  name  imports,  to  show  the  difference 
of  temperature  between  two  places  at  short 
distances  from  each  other.  It  consists  of  a 
glass  tube  terminated  at  each  end  by  a  bulb, 
and  bent  as  shown  in  the  figure.  The  tube 
is  partly  filled  with  some  colored  fluid,  as 
sulphuric  acid  tinged  with  carmine,  or  alco- 
hol co'ored  by  cochineal,  the  bulbs  and  other 
parts  of  the  tube  being  filled  with  air.  It 
is  obvious,  from  the  construction  of  this  in- 
strument, that  it  can  not  indicate  the  tem- 
perature of  the  atmosphere,  since  an  equal 
expansion  of  the  air  in  both  bulbs  A\ould 
press  equally  on  the  fluid  in  bolh  arms  of 
the  tube,  and  consequently  it  would  ri>e  in 
neither.  But  if  one  bulb  be  exposed  to  a 
higher  temperature  than  the  o'her,  then,  the 
expansion  of  air  in  this  will  be  greater  than  in  the  other,  and 


Fig.  46. 

O     O 


Differential  Therr 
moineter, 


129.  Describe  Leslie's  differential  thermometer.    What  is  its  most  important  use? 


THE    MERCURIAL    THERMOMETER.  103 

consequently  the  fluid  will  move  toward  the  bulb  in  which  the 
air  is  least  expanded.  The  use  of  this  thermometer  consists  in 
showing  the  difference  of  temperature  to  which  the  bulbs  are 
exposed,  as  in  the  experiments  on  the  radiation  of  heat,  already- 
described.  The  scale  affixed  to  one  of  the  arms  is  divided  into 
100  degrees,  and  indicates  the  amount  of  expansion.  The  arms 
are  six  inches  long,  and  the  bulbs  an  inch,  or  a  little  more,  in 
diameter.  It  is  of  special  advantage  in  detecting  the  amount  of 
heat  which  proceeds  from  any  given  source,  such  as  that  which  is 
transmitted  through  rock  salt,  in  experiments  on  diathermancy, 
without  danger  of  part  of  the  effect  being  due  to  some  extraneous 
so-irce,  as  for  instance  the  heat  of  a  neighboring  fire  or  lamp. 
This  extraneous  heat,  though  it  would  affect  a  common  ther- 
mometer, exerts  no  influence  upon  the  differential  thermometer, 
>o  that  wha'ever  effect  is  produced  upon  it,  is  due  exclusively  to 
the  particular  source  of  heat  which  is  employed. 

130.  The  mercurial  Thermometer.  Aeriform  fluids  being 
inapplicable  to  the  construction  of  thermometers  lor  the  purpo  e 
of  measuring  the  varying  temperature  of  places  and  things,  on 
account  of  their  great  expansibility,  it  is  necessary  to  make  use 
of  solids  or  liquids.  Solid  bodies,  however,  are  equally  unfit- 
ted for  this  purpose,  from  an  opposite  property,  their  slight  ex- 
pansibility, it  being  so  small  as  not  to  be  appreciable  without 
the  adaptation  of  complicated  machinery,  A  perfect  substance 
for  this  purpose  would  be  a  fluid,  which  would  expand  uni- 
formly with  equal  increments  of  heat,  and  neither  freeze 
nor  boil  at  any  temperature  to  which  it  might  bo  exposed. 
Mercury  approaches  nearer  to  these  conditions  than  any  other 
substance,  and  therefore,  this  is  the  fluid  now  almost  universally 
employed,  Its  boiling  point  is  6G2°,  and  its  freezing  poinU-40°, 
which  enables  it  to  measure  a  very  wide  range  of  temperature ; 
and  it  possesses  also  this  singular  advantage,  that  though  it  ex- 
p  vnds  more  for  an  equal  increment  of  heat  at  a  high  than  a  low 
temperature,  this  additional  expansion  is  corrected  by  the  in- 
creased capacity  of  the  glass  bulb  and  tube  which  contain  it>  so 
that  the  indications  of  the  instrument  are  very  nearly  correct 
for  all  temperatures  between  freezing  and  boiling  water ;  for 
higher  temperatures  the  compensation  is  not  so  exact,  Th« 
total  expansion  of  mercury  for  three  progressive  intervals 
of  180°  F.  is,  between  32Q  and  212°,  1  part  in  55.08 ;  between 

•    130.  Describe  the  mercurial  thermometer.    Why  is  mercury  a  good  thermometrio 

fluid .' 


104  CONSTRUCTION    OF   THERMOMETERS. 

212°  and  392°,  1  in  54.61 ;  between  392°  and  572°,  1  in  54.01, 
The  temperature  of  572°  F.,  as  measured  by  an  air-thermome- 
ter, if  measured  by  the  expansion  of  mercury,  in  an  ordinary 
thermometer,  would  be  indicated  as  586°,  showing  that  the 
expansion  of  the  mercury  increases  as  the  temperature  ri  es. 

131.  Construction  of  the  Thermometer.  The  blowing  of 
an  accurate  thermometer-tube  and  bulb  requires  much  experi- 
ence, is  performed  only  by  skillful  artists,  mid  is  the  most  diffi- 
cult part  of  the  construction  of  the  instrument.  The  delicacy 
of  a  thermometer  depends  upon  the  fineness  of  the  bore  of  the 
tube,  and  the  large  size  of  the  bulb.  The  bore  must  also  be 
of  equal  calibre  throughout ;  this  is  determined  by  introducing 
a  small  portion  of  mercury,  and  then  ascertaining  by  means  of 
a  pair  of  dividers  if  it  occupies  the  same  space  in  all  portions 
of  the  tube.  The  bore  being  extremely  fine,  the  mercury  can 
only  be  introduced  by  heating  the  bulb,  expelling  a  portion  of 
the  air  within  it,  and  then  inverting  the  open  end  of  the  tube 
into  a  vessel  of  the  liquid  metal.  As  the  air  within  contracts 
by  cooling,  the  pressure  of  the  external  atmosphere  forces  the 
mercury  to  enter  the  tube  in  order  to  supply  its  place.  The 
bulb,  and  about  one-third  of  the  tube  having  4hus  been  filled,  a 
spirit  lamp  is  applied  to  the  bulb,  until  the  mercury  has  been 
made  to  boil,  and  driven  to  the  extreme  upper  end  of  the  tube. 
By  this  process  the  air  and  moisture  mixed  with  the  mercury 
are  completely  expelled.  At  this  instant,  before  the  lamp  is 
withdrawn,  and  while  the  mercury  still  completely  fills  the  stem, 
the  flame  of  the  blow-pipe  is  darted-across  the  end  of  the  tube, 
and  it  is  immediately  melted  up,  or  hermetically  sealed.  When 
the  lamp  is  removed  the  mercury  contracts  to  its  former  dimen- 
sions, leaving  a  vacuum  between  itself  and  the  extremity  of  the 
tube.  Consequently  there  is  no  aeriform  fluid  to  be  compressed 
by  the  mercury  as  it  expands,  and  by  its  reaction  keep  the  level 
of  the  liquid  below  the  point  it  should  properly  reach.  For 
this  reason,  in  a  properly  constructed  thermometer,  if  the  tube 
be  inverted,  the  mercury  will  freely  run  to  the  extremity  of 
the  instrument,  there  being  no  air  within  the  tube  to  impede 
its  motion. 

Having  sealed  the  end  of  the  tube,  the  next  step  in  the  con* 
struction  of  the  thermometer  is  its  graduation.  This  is  done 
by  marking  two  fixed  and  invariable  points  on  the  stem, 

131.  Describe  the  construction  of  the  thermometer.    How  is  the  air  expelled  ?    What 
are  the  fixed  points  of  the  scale  ? 


FAHRENHEIT'S  SCALE.  105 

which  indicate  the  same  temperatures  in  every  thermometer,  and 
then  making  a  scale  of  equal  divisions  between  the?e  two  points. 
These  are  the  freezing  an:l  boiling  points  of  water  which,  under 
the  same  circumstances,  always  indicate  constant  temperatures. 
The  freezing  point  is  found  by  immersing  the  bulb  of  the  ther- 
mometer in  melting  snow  or  ice,  for  it  has  been  ascertained  that 
the  temperature  of  water  flowing  from  melting  snow  or  ice  is 
everywhere  the  same,  whatever  may  be  the  heat  of  the  atmos- 
phere where  the  experiment  is  made.  The  boiling  point  is  slightly 
affected  by  a  variation  in  the  pressure  of  the  atmo  phere  ;  but 
the  thermometer  will  be  sufficiently  accurate  for  all  ordinary 
purposes,  when  this  point  is  ascertained  by  immersing  the  bulb 
in  pure  boiling  water,  open  to  the  air,  and  at  the  level  of  the  sea, 
during  pleasant  Aveather.  The  freezing  and  boiling  points  are 
marked,  with  a  diamond  or  file,  on  the  tube,  and  a  scale  is  at- 
tached, upon  which  the  degrees  are  clearly  marked.  The  inter- 
val between  these  points  is  differently  divided  in  different  coun- 
tries. In  England  and  the  United  States,  the  division  generally 
adopted  is  that  of  Fahrenheit. 

132.  Fahrenheit's  Scale.  Fahrenheit  was  a  philosophical 
instrument  maker  of  Amsterdam,  who  constructed  thermome- 
ters in  so  adm'rable  a  manner  that  they  soon  spread  all  over 
Europe.  On  his  scale  the  freezing  point  of  water  was  marked 
at  32°,  and  the  boiling  point  at  212°.  The  interval  between 
these  two  points  was  then  accurately  divided  iiro  180  equal 
parts,  called  degrees,  which  are  continued  below  32°  to  0°,  and 
above  212°  as  high  as  G62°,  or  the  boiling  point  of  mercury,  if 
need  require.  The  scale  is  often  carried  much  lower  than  0°, 
and  in  this  case  the  decrees  always  have  the  prefix  —  minus, 
to  indicate  this  fact.  Thus  —  40°  indicates  a  temperature  40° 
below  0°.  The  scale,  therefore,  really  commences  at  32°  below 
the  freezing  point  of  water,  this  being  the  point  at  which  the  0° 
is  placed ;  the  freezing  point  of  water  is  placed  at  32°,  and  the 
boiling  point  of  water  at  212°,  and  when  a  higher  or  lower 
temperature  is  to  be  measured,  the  scale  of  equal  parts,  as  has 
been  stated,  is  continued  beyond  these  points.  It  has  been 
thought  that  Fahrenheit  took  the  zero,  or  commencement  of  his 
scale  from  the*  degree  of  cold  produced  by  mixing  snow  and 
common  salt,  that  being  the  greatest  degree  of  cold  known  in 
his  time.  The  zero  was,  however,  in  reality,  taken  from  the 
greatest  cold  observed  in  Iceland,  and  the  principle  which  dictated 

132.  Describe  Fahrenheit's  scale. 


106 


OTHER    SCALES. 


tlie  peculiar  division  of  the  scale  was  the  following.      When  the 

instrument  stood  at  the  greatest  cold  of  Iceland,  or  at  0°,  it  was 
computed  to  contain  11,124  equal  parts  of  mer- 
Fig.  47.  cury,  which,  when  plunged  in  melting  snow,  or 
freezing  water,  expanded  to  11,156  parts  ;  hence 
the  intermediate  space  was  divided  into  32  equal 
portions,  and  32°  was  taken  as  the  freezing  point 
of  water.  When  the  thermometer  was  plunged 
into  boiling  water  the  mercury  was  expanded  to 
11,336  parts,  and  therefore  212°  was  marked  as 
boiling  point.  Though  the  principle  on  which 
this  scale  is  founded  is  not  reliable,  yet  it  pos- 
sesses in  practice  decided  advantages  over  every 
other  on  account  of  its  extensive  range  and  the 
lowness  of  its  0°,  which  ordinarily  dispenses  with 
the  necessity  for  using  negative  degrees,  and  also 
on  account  of  the  smallness  of  its  degrees  which 
makes  the  use  of  fractions  unnecessary. 

133.  Other  Thcrmomctric  Scales.  Besides 
the  scale  of  Fahrenheit,  in  which  the  distance 
between  the  freezing  and  boiling  points  is  divided 
into  180  equal  parts,  there  are  in  use  in  France  arid 
on  the  Continent  in  general,  two  other  scales,  the 
Centigrade  and  Reaumur's.  In  the  -former,  the 
distance  between  the  freezing  and  boiling  points 
is  divided  into  100  equal  parts,  the  0°  being  placed 
at  the  former,  and  100°  at  the  latter.  In  Reau- 
mur's scale,  0°  is  placed  opposite  to  the  freezing 
point,  and  80°  opposite  to  the  boiling  point. 
Consequently,  212°  F.  correspond  to  100°  C.  and 
to  80°  R.,  and  32°  F.  correspond  to  0°  C.  and  0° 
R.  In  order  to  compare  the  e  scales  together  it 
is  necessary  to  resort  to  calculation.  The  first 
tiling  to  be  done  is  to  establish  the  ratio  of  the 
scales ;  and  as  the  number  of  degrees  between 
the  freezing  and  boiling  points  of  water  in  the 
three  scales  are  180,  100,  and  80,  the  scales  con- 
sequently bear  these  proportions  to  each  other, 

which  by  reduction  to  their  lowest  terms  become  9,  5,  and  4. 

Consequently  the  Centigrade  and  Reaumur  degrees  are  larger 


Merntrial  Ther- 
mometer. 


•  1C3.  Describe  the  Centigrade  smle.     That  of  Reaumur      Reduce  140°  Fahrenheit  to 
Centigrade.     Reduce  140°  Jb\  to  Reaumur. 


CENTIGRADE,    REAUMUR.  107 

than  those  of  Fahrenheit,  5°  of  C.  and  4°  of  R.  being  equal  to 
9°  of  F.  If,  then,  it  be  required  to  reduce  140°  F.  to  the  Cen- 
tigrade scale,  we  first  subtract  32°  from  140°,  because  the  two 
scales  do  not  start  at  the  same  point,  but  the  Centigrade  begins 
at  a  temperature  32°  higher  than  Fahrenheit;  this  gives  us 
108°.  Then,  as  the  scale  F  is  to  the  scale  C  as  180  is  to  100, 
we  establish  this  proportion :  180 : 100 : :  108  :  x,  or  9  : 5  : :  108  :  x ; 
reducing,  we  have  J.£f*£=a?,  or  £±Q-=x,  x=QO°of  the  Centi- 
grade scale.  Consequently  140°  Fahrenheit  are  equal  to  60° 
of  the  Centigrade  scale.  To  reduce  140°  F.  to  Reaumur,  we 
first  subtract  32°  as  before,  and  then  establish  the  proportion 
180  : 80  : :  108  :  x,  or  9  : 4 : :  108  :  x ;  reducing,  we  have  -Lfi§*± 
=x,  or  i|^^=x;  #=48°  Reaumur.  Consequently,  140°  Fah- 
renheit are  equal  to  48°  of  the  scale  of  Reaumur.  In  re- 
ducing Centigrade  and  Reaumur  to  Fahrenheit,  we  reverse  the 
process  and  add  32°  to  the  answer,  instead  of  subtracting  it,  for 
the  reason  already  explained.  Thu*,  to  reduce  60°  Centigrade 
to  Fahrenheit,  we  have  100  : 180  : :  60  :  x,  or  5  :  9  : :  60  :x;  reduc- 
ing, we  have  &.<g3.=x,  or  ^a=aj;  #^108°  F. ;  adding  32°  we 
obtain  60°  C.  =  140°  F.  To  reduce  48°  Reaumur  to  Fahren- 
heit, we  have  80  : 180  : :  48  :  x,  or  4 :  9  : :  48  :  x ;  reducing,  we 
have  i-^rrrtf,  Or  ±iz=x\  #=108°  F. :  adding  32°  we  obtain 
48°  R.,=140°  F.  The  following  formulae,  express  the  steps 
of  these  calculations  very  clearly : 

(F— 32)  X5 
Fahrenheit  to  Centigrade,  ~   — ^ —     -  —  *-" 

CX9 
Centigrade  to  Fahrenheit,  — ^— +  32— :R|r     • 

(F— 32)X4 
Fahrenheit  to  Reaumur,          — 5— (  '  * 

KX9 
Reaumur  to  Fahrenheit,    — ^-— -f-32=F. 

Sometimes  thermometers  have  two  scales  attached  to  the 
same  stem,  as  in  Fig.  47,  where  Fahrenheit's  scale  is  placed  o'i 
the  right  hand,  and  the  Centigrade  on  the  left.  With  such  an 
arrangement  there  is  no  necessity  for  any  calculation.  This 
arrangement  is  still  further  improved  by  graduating  the  gin  s 
tube  itself  with  one  of  the  scales,  and  placing  the  other  two 
upon  the  sides. 

How  are  Centigrade  and  Reaumur  reduced  to  Fahrenheit?  Explain  the  principle  of 
these  reductions.  Saow  how  reduction  may  be  obviated  by  thermometer  with  two  scales, 
or  with  three. 


108 


REGISTER    THERMOMETERS. 


134.    Different  Forms  of  the  Thermometer.      The    ther- 
mometer is  arranged  in  many  different  forms,  but  in  all,  the 
principle  is  the  same.     For  u-e  in  the  laboratory  it  is  specially 
advantageous    to   avoid    the    employment  of 
Fig.  46.  wooden,  ivory,  or  metallic  scales,  on  account 

of  their  liability  to  corrosion  from  gases  and 
liquids.  The  best  chemical  thermometers  are 
therefore  constructed  with  scales  cut  upon  the 
glass,  as  in  Fig.  48,  which  represents  two 
thermometers  graduated  on  the  tube,  and 
with  bulb.s  elongated  in  order  to  render  the 
mercury  more  susceptible  to  variations  of 
temperature. 

135.  Register  Thermometers.  Several 
methods  have  been  devised  to  make  ther- 
mometers mark  temperature  in  such  a  man- 
ner as  to  leave  permanent  indications  of  the 
highest  and  lowest  points  which  the  mercury, 
has  attained  since  the  last  observation.  Thus, 
in  attempting  to  find  the  temperature  of  the 
deep  ocean  by  the  common  thermometer,  it  is 
easy  to  see  that  the  object  would  be  defeated  by 
the  increase  in  the  temperature  of  the  water  as 
the  instrument  is  drawn  toward  the  surface.  If, 
however,  a  mark  could  be  left  at  the  point 
where  the  mercury  stood  when  it  was  at  the 
greatest  depth,  then  the  object  in  question 
would  be  attained,  and  this  is  what  the  self- 
registering  thermometer  performs.  It  also 
indicates  the  highest  and  lowest  temperatures 
which  may  be  reached  during  the  day  or 
night,  in  the  absence  of  the  observer.  One 
of  the  simplest  and  most  efficient  forms  of  this 
-  instrument  was  invented  by  Rutherford,  and 
bears  his  name.  It  is  represented  in  Fig.  49, 
and  consists  of  two  thermometers,  with  their  bulbs  bent  at  right 
angles  to  the  stem,  and  placed  in  an  inverted  position  in  refer- 
ence to  each  other.  The  upper  one  is  filled  with  mercury,  the 
lower  with  alcohol.  In  the  former  a  small  piece  of  steel  is  in- 
troduced, which  is  pushed  forward  by  the  expansion  of  the 


134.  Describe  different  forms  of  the  thermometer. — 133.  Describe  Rutherford's  Regis- 
tt-r  thermometer. 


METALLIC    THERJIOHETCRS. 


109 


mercury,  and  left  when  it  again  contracts.     The  lower  side  of 
the  steel  indicates,  therefore,  the  highest  point  which  the  raer- 


'20 


10 


10 


20          30  40 


Rutherford's  'Register   Thermometer. 

cury  has  reached  during  the  absence  of  the  observer.  In  the 
latter,  there  is  inserted  a  small  bit  of  glass,  which  floats  in  the 
alcohol,  and  is  carried  down  by  it,  when  it  contracts.  When  it 
expands  again,  the  bit  of  glass  is  not  pushed  forward,  but  is  left 
at  the  point  at  which  the  alcohol  remained  stationary.  Thus 
the  upper  end  of  the  bit  of  glass  indicates  the  lowest  point  to 
wlii  -h  the  thermometer  has  sunk  during  the  absence  of  the  ob- 
server. It  is  evident  that  the  instrument  needs  to  be  adjusted 
before  it  can  give  these  indications  a  second  time.  Thi>  is  ac- 
complished by  inclining  it  upon  the  end  towards  the  left  and 
gently  tapping  the  instrument.  The  steel  descends  to  the  level 
of  the  mercury,  and  the  piece  of  glass  flows  down  to  the  end  of 
the  alcoholic  column.  The  thermometer  is  then  adjusted  and 
fitted  to  make  a  second  registration. 

136.  Metallic  Thermometers.  When  it  is  desired  to  meas- 
ure temperatures  lower  than  the  degree  at  which  mercury 
freezes,  i.  e. — 40°,  it  is  necessary  to  use  thermometers  filled 
with  alcohol,  a  liquid  which  has  never  yet  been  solidified. 
On  the  other  hand,  when  it  is  desired  to  measure  temperatures 
higher  than  the  degree  at  which  mercury  is  converted  into  a 
vapor,  we  must  employ  thermometers  made  of  metal.  Metallic 
thermometers  depend  upon  the  expansion  and  contraction  of 
solids,  multiplied  by  means  of  machinery  and  accurately  meas- 
ured by  a  gradual  ed  scale.  In  Fig.  50,  there  is  a  representa- 
tion of  Breguet's  metallic  thermometer.  It  consists  of  a  strip  of 
metal,  composed  of  slips  of  platinum,  gold  and  silver,  which,  after 
being  soldered  together,  are  roiled  into  a  thin  ribbon,  which  is  then 


133.  Why  are  metallic  thermometers  useful  ?   Describe  Breguet's  metallic  thermometer 


110 


PYROMETERS. 


Breguefs  Metallic  Thermometer. 


iS-  5°-  formed  into  a  spiral  or  helix. 

The  silver,  which  is  the  mo^t 
expansible  of  these  three 
metals,  is  placed  upon  the 
outside  of  the  helix  ;  the  pla- 
tinum on  the  inside,  and  the 
gold  between  the  two.  One 
end  of  the  spiral  is  fixed,  the 
other  is  connected  with  an 
index,  and  graduated  circle. 
As  the  temperature  rises,  the 
silver  expanding  the  most, 
twists  the  spiral  and  causes 
the  index  to  move  from  left 
to  right.  When  the  tempera- 
ture falls,  the  spiral  turns  in 
the  opposite  direction.  It  is  an  exceedingly  delicate  and  beauti- 
ful instrument.  There  are  others  constructed  upon  the  same 
plan,  but  Arranged  in  a  more  compact  and  convenient  form. 

137.  Pyrometers.  This  name  is  given  to  instruments  in- 
tended to  measure  high  degrees  of  temperature,  such  as  the 
heat  of  furnaces  and  kilns.  The  most  celebrated  is  the  one 
invented  by  ProK  Daniell, depending  for  its  act'on  upon  the 
expansion  of  a  rod  of  platinum.  The  amount  of  the  expansion 
is  measured  by  nicely  adjusted  scales.  Platinum  is  infusible  at 
most  artificial  temperatures,  and  is  therefore  well  fitted  to  test 
the  heat  of  the  hottest  furnaces.  Wedgewood's  pyrometer  de- 
pends upon  the  contraction  of  bits  of  clay,  by  heat,  in  conse- 
quence of  the  loss  of  water,  which  they  suffer  when  placed  in 
a  very  hot  furnace.  The  amount  of  this  contraction  is  meas- 
ured by  a  scale,  and  thus  it  affords  a  tolerably  accurate  measure 
of  temperature.  By  means  of  Daniell's  pyrometer  it  has  been 
ascertained  that  red  heat  takes  place  at  about  980°  F. ;  silver 
melts  at  1  873°  ;  cast  iron,  2  786°  ;  gold,  2  016°  ;  and  that  the 
highest  heat  of  a  wind  furnace  is  about  3  280°. 

Experiments :— Effects  of  Heat:    Expansion. 

1.  Expansion  of  Solids.     That  solids  expand  from  heat  may  be  shown  by  fitting 
a  brass  rod,  provided  with  a  wooden  handle,  into  an  iron  plate,  cut  FO  as  just  to  rtc  eive 
it.     Heat  t!ie  rod  and  it  will  no  longer  enter  this  cavity.     Cool  it  by  immersion  in  a  freez- 
ing mixture,  and  it  will  enter  it  much  more  easily  than  it  did  at.  first. 

2.  Heat  any  metallic  ball,  and  it  will  no  longer  pass  through  a  hole  in  a  plate  of  cop- 


137.  What  are  pyrometers?      Describe  Daniell's  pyrometer.      Describe  Wedgewood's. 
Heution  some  of  the  temperatures  determined  by  the  pyrometer. 


EXPERIMENTS  111 

'per  or  a  ring,  through  -which,  when  cold,  it  easily  passed.  Allow  it  to  cool  and  it  recov- 
ers its  original  dimensions. 

3.  To  show  thac  different  metals  expand  unequally  for  the  same  additions  of  heat,  ex- 
pose rods  of  different  metals  to  tiie  same  source  of  iieat,  i.  e.,  the  same  lamp  for  an  equal 
length  of  time,  and  measure  the  expansion  by  the  moving  of  au  index  over  a  graduate! 
arc  ot  a  circle,  as  in  the  ordinary  pyrometer:  the  expantiou  will  be  different  in  each  cate. 

t.  Kivet  together  along  their  whole  length,  two  strips  of  brass  and  zinc,  and  throw  the 
compound  strip  into  a  vessel  of  boiling  water.  It  will  be  curved  by  the  greater  expan- 
sion of  the  more  expansible  metal,  the  zinc. 

5.  Throw  the  same  compound  strip  into  a  freezing  mixture  of  ice  and  snow,  or  ice 
water,  and  it  will  be  bent  in  the  opposite  direction,  by  the  greater  contraction  of  tiie 
same  metal 

6.  That  solids  expanded  by  heat  return  to  their  original  dimensions  when  pernvltt  1 
to  resume  their  former  temperature  is  shown  by  experiment  2.  \\ith  ball  and  ring;  ak-o 
by  suspending  a  56  ib.  weight  by  an  iron  wire  from  the  ceiling  in  such  a,  way  as  to  jus-t 
clear  a  block  placed  under  the  weight ;  then  tie  upon  the  wire,  at  intervals  of  a  foot,  bits 
of  tow  ;  saturate  them  with  alcohol  and  apply  a  match.     The  wire  will  be  lengthened  by 
tie  expansion,  and  the  weight  no  longer  clear  the  block.    Allow  the  wire  to  cool  and  the 
weig.it  will  be  drawn  up  to  its  former  position. 

7.  That  poor  conductors  of  heat  are  readily  broken  by  sudden  heating  is  shown  by 
applying  a  hot  iron  to  a  glass  flask  ;  it  will  be  broken  along  the  path  of  the  i  on. 

8.  Invert  a  bottle  having  a  glass-stopper,  and  cautiously  heat  the  neck  of  the  bottle 
on  the  outside  with  a  spirit  lamp  ;  the  stopper  will  sooa  drop  out,  showing  the  real  ex- 
pansion of  the  glass  when  slowly  heated. 

9.  Grind  a  glass  rod  accurately  into  a  hole  in  a  metallic  plate,  and  then  heat  slowly  in 
a  spirit  lamp,  or  by  immersion  in  hot  water  ;  it  will  no  longer  fit  the  hole. 

1 0.  Heat  the  glass  stopper  of  a  bottle,  and  it  will  no  longer  enter  the  mouth  of  the 
bottle. 

11.  Expansion  of  Liquids.    To  show  that  liquids  expand,  dip  the  bulb  of  a 
'thermometer  into  hot  water. 

12.  Fit  a  cork,  with  a  long  tube  passing  through  it,  into  a  flask  filled 'with  water. 
The  water  will  rise  into  the  tube  three  or  four  inches  ;  tie  a  string  around  the  tube  at 
the  level  of  the  liquid,  and  dip  the  tiask  into  hot  water;  first  the-  water  will  sink  and 
then  rise  very  rapidly  in  the  tube. 

1  3.  Fill  a  large  test  tube  entirely  full  of  alcohol,  and  then  place  it  carefully  in  a  jar 
of  hot  water;  it  wi.l  very  soon  overflow  the  rim.  Or,  fill  a  flask,  like  that  described  in 
the  preceding  experiment,  12,  with  alcohol  colored  red  by  cochineal,  and  note  the  addi- 
tional amount  of  expansion. 

14.  Fill  a  dropping  tube  entirely  full  of  sulphuric  ether  or  alcohol  and  apply  heat  to 
the  bulb,  the  thumb  being  applied  to  the  larger  end.  Tiie  liquid  will  be  forced  out 
through  the  small  orii  ce,  in  a  steady  stream. 

1  5.  That  different  liquids  expand  unequally  from  the  same  increments  of  heat  is 
shown  by  filling  two  buibs,  of  the  same  size,  one  with  alcohol,  and  the  other  wit.i  water, 
to  the  same  heigat,  and  dipping  them  into  the  same  vessel  of  hot  water  ;  or  by  filling  a 
large  bulb  to  a  certain  point  first  with  water,  and  placing  it  for  ten  minutes  in  a  ve.-sel 
of  boiling  water;  then  emptying  it,  cooling  in  cold  water,  filling"  it  with  alcohol  to  the 
same  point,  and  exposing  it  for  ten  minutes  in  the  same  vessel  of  boiling  water.  Note 
the  difference  in  the  expansion  in  the  two  cases  by  means  of  scale. 

lt>.  Apparent  Paradox  Dip  a  flask  of  water,  with  tube,  as"  in  experiment  12,  into  a 
vessel  of  boiling  water  The  wate-  for  a  few  seconds  will  sink  considerably  in  tne  tube, 
instead  of  rising  This  is  owing  to  the  expansion  of  the  glass  flask,  by  which  its  capacity 
is  increased. 

17.  Immerse  the  same  flask  in  a  vessel  of  ice  and  water  ;  the  liquid  will  rise  instead 
of  sinking,  owing  to  the  diaiiuished  capacity  of  the  flask. 

18.  Expansion  of  Gases.     That  gases  expand  from  heat  is  shown  by  applying 
heat  to  the  bulb  of  the  large  air  thermometer,  described  in  Art.  128.     Fig.  45. 

19.  Invert  a  glass  tube,  having  a  long  bulb  at  the  end  like  a  large  thermometer  tube, 
in  water  colored  blue  by  sulphate  of  copper :  support  it  so  that  its  l>eak  just  dips  beneatii 
the  level  of  the  liquid ;  apply  the  flame  of  a  lamp  and  the  air  will  be  driven  out,  showing 
expansion  :  remove  the  lamp  and  the  liquid  will  rise  into  the  stem,  showing  contraction  , 
apply  heat  again  and  the  air  will  again  expand,  driving  the  colored  water  down  before 
it.     This  forms  a  simple  air  tiuTmomc'er. 

20.  He  it  a  well  corked  empty  bottle  by  immersing  it  in  hot  water,  or  exposing  it  to 
the  fire:  the  cork  will  be  driven  out. 

21.  Heat  a  tightly  closed  India  rubber  bag,  partially  filled  with  air ;  it  will  distend, 
and  finally  be  ruptured 

22.  Exception  by  W*.*«*r  to  the  Law  of  Expansion.     Provide  a  flask, 
similar  to  the  one  used  in  experiment  12,  but  having  a  thermometer  also  passed  tightly 


112  ON   EXPANSION. 

through  the  cork ;  mark  the  height  of  the  water  by  a  string,  and  note  the  temperature. 
Then  immerse  in  a  freezing  mixture  of  pounded  ice  or  snow,  and  salt ;  the  water  will 
steadily  sink  in  the  tube  until  the  thermometer  indicates  about  40^  ;  as  the  temperature 
decreases,  the  water,  instead  of  obeying  the  same  law,  begins  to  expand,  and  continues 
to  do  so  until  the  thermometer  indicates  the  temperature  of  32°,  when  it  will  suddenly 
shoot  up  and  overflow  the  end  of  the  tube,  on  account  of  the  freezing  of  the  water  in 
the  liask.  In  consequence  of  this  exception,  cold  water  at  82°  floats  on  the  top  of  waim- 
er  water  at  40°. 

2  3.  Repeat  the  experiment  described  in  Art.  123.  taking  care  to  fill  the  brass  cup  with 
a  mixture  of  ice  and  salt,  instead  of  ice  alone. 

24.  Thermometers.     Test  the  freezing  and  boiling  points  by  immersing  them  in 
melting  ice  and  boiling  water ;  the  mercury  should  stand  in  the  one  case  at  82°  ;  in  the 
other  at  2120. 

25.  Note  the  temperature  at  which  water  boils  in  a  glass  flask,  and  observe  the  eCect 
Of  throwing  in  some  iron  tilings. 

26.  Invert  a  thermometer  and  observe  if  the  mercury  runs  to  the  end  of  the  stem. 

27.  Squeeze  the  bnib  between  the  fingers  and  note  the  rising  of  the  mercury.     This 
phows  the  elasticity  of  the  glass.    The  thermometer  in  this  experiment  should  stand  at 
1000. 


§  XII.    Effects  of  Heat :- Liquefaction. 

138.  Heat  of  Composition.  It  has  been  stated  that  heat  ex- 
ists in  two  states  :  first,  as  heat  of  temperature  ;  second,  as  heat 
of  composition.  Having  considered  the  effects  of  heat  in  the  first 
of  these  states,  we  now  proceed  to  consider  those  which  it  produces 
rin  the  second.  When  heat  merely  flows  into  a  body,  without  com- 
bining wilh  it,  the  only  effect  produced  is  an  elevation  of  tempera- 
ture, together  with  a  proportionate  enlargement  of  its  dimensions  ; 
but  when  it  enters  into  a  body  so  as  to  combine  with  it,  the  body  is 
changed  from  the  state  of  a  solid  to  that  of  a  liquid,  or  from  the 
state  of  a  liquid  to  that  of  a  vapor.  In  this  case  a  portion  of  the 
heat  disappears ;  the  whole  of  the  heat  which  enters  the  body  does 
not  appear  as  heat  of  temperature,  but  a  portion  is  expended  in 
changing  its  state.  The  heat  no  longer  appears  as  heat ;  the 
solid  into  which  it  has  entered  no  longer  appears  as  a  solid. 
The  heat  and  the  solid  have  combined  so  as  to  form  a  new 
liquid  or  gaseous  substance,  differing  essentially  in  its  appear- 
ance and  properties  from  both  the  substances  which  have  en- 
tered into  it.  The  process  is  analogous  to  that  which  takes 
place  when  the  two  invisible  gases,  oxygen  and  hydrogen,  mine 
to  form  the  visible  substance,  water,  differing  in  all  respects 
from  the  two  elements  which  have  combined  to  form  it.  It  is  a  • 

138.  What  are  the  two  states  in  which  heat  exists?  What  are  the  effects  produced 
upon  bodies  by  heat  of  temperature?  What  are  the  effects  produced  upon  bodies  when 
heat  enters  into  composition  with  them?  What  change  of  state  is  produced  by  heat  of 
composition  ?  Wueu  two  *ub»Uucu.s  combine,  what  i>  tha  universal  law  ? 


LIQUEFACTION    PRODUCED    BY   HEAT. 


113 


universal  law  that  when  two  substances  combine,  the  compound 
formed  possesses  properties  different  from  those  of  the  compo- 
nent elements.  In  this  view,  water  is  a  compound  of  ice  and 
hea" ;  melted  iron  is  a  compound  of  solid  iron  and  heat,  be- 
cau-e  in  both  these  combinations  a  large  amount  of  heat  has 
combined  with  the  ice  and  iron,  and  no  longer  appears  possessed 
of  its  mo^t  striking  property,  viz.,  the  power  to  elevate  tempera- 
ture ;  while  at  the  same  time  both  the  ice  and  iron  have  lost  all 
their  solid  properties  and  been  converted  into  liquids.  The  first 
of  the  effects  of  combined  heat  is  Liquefaction;  the  second, 
Vaporization. 

139.  Liquefaction  produced  by  Heat. — Melting-  Point. 
When  heat  enters  a  solid  its  first  effect  is  to  produce  expansion ; 
as  it  accumulates,  the  particles  gradually  become  so  far  separa- 
ted as  to  move  easily  upon  each  other  and  readily  change  their 
position,  and  finally,  if  the  heat  be  increased  still  further,  a  state 
of  complete  liquidity  is  the  result.  This  process  is  called  Lique- 
faction. The  degree  at  which  it  takes  place  is  different  for  dif- 
ferent substances,  and  is  called  the  melting  point.  Ice  melts  at 
;  sulphur  220°;  tin  442°;  Iead612°i 
iron  2786° ;  silver  1 873° ;  gold  201 6°. 
140.  Disappearance  of  a  large 
amount  of  Heat  during  Liquefaction. 
The  most  important  fact  connected 
with  liquefaction,  is  the  disappear- 
ance and  absorption  of  a  large 
amount  of  heat.  The  fact  of  this 
absorption  may  be  easily  proved.  If 
a  flask  full  of  ice  at  0°,  with  a  ther- 
mometer inserted  in  it,  be  placed 
over  a  fire,  the  mercury  will  immedi- 
ately commence  rising,  and  continue 
to  do  so  until  it  has  attained  the 
temperature  of  32°  ;  but  when  it  has 
reached  this  point  it  will  suddenly 
stop  and  refuse  to  rise  any  higher. 
Fig.  51,  This  elevation  of  tempera- 
ture in  the  ice  takes  place  without  the 
melting  of  any  portion,  however  small. 


32°F.;  spermaceti  at  132C 
Fig.  61. 


Absorpt'on  of  Hfat  in 
L.'n;uf faction. 


In  this  light  what  may  melted  iron  be  regarded  as  composed  of  ?— 139,  What  is  the 
cause  of  liquefaction  ?  Is  the  temperature  at  which  it  takes  place  the  same  in  all  sub- 
stances ?  Give  the  melting  points  of  different  substances. — 140,  What  is  the  most  im- 
port mt  fxct  connected  with  liquefaction  ?  How  may  the  absorption  of  heat  in  liquefo^ 
tion  be  shown  ? 


lu 


ABSORPTION    OF   HEAT    IN    LIQUEFACTION. 


As  soon,  however,  as  the  thermometer  has  risen  to  32°,  the  ico 
ceases  to  indicate  any  increase  of  temperature,  and  begins  to 
melt  very  slowly.  Now  it  is  evident  that  in  the  five  minutes 
immediately  after  the  thermometer  has  ceased  to  rise,  the  ice 
must  be  receiving  heat  at  the  same  rate  as  it  did  in  the  five  min- 
utes immediately  before.  What  has  become  of  this  heat,  since 
it  produces  no  effect  on  the  thermometer  ?  It  has  evidently  dis- 
appeared and  been  absorbed  in  the  process  of  liquefaction,  and 
its  force  has  been  exj  ended  in  effecting  this  change  of  state. 
It  has  combined  with  the  ice  and  produced  a  substance  in  which 
neiiher  its  own  properties  as  heat,  nor  those  of  the  ice,  as  a  folid, 
any  longer  appear.  The  heat  thus  absorbed  is  said  to  have  be- 
come latent,  and  the  amount  of  it  varies  with  the  particular  solid 
substance  which  is  liquefied. 

141.  Amount  of  Heat  absorbed  in  the  melting-  of  Ice.  In 
the  liquefaction  of  ice,  the  heat  absorbed  is  sufficient  to  raise 
the  temperature  of  an  equal  weight  of  water  140°.  Thus,  if  a 
pound  of  ice  be  melfed,  the  heat  absorbed  is  sufficient  to  raise 
the  temperature  of  a  pound  of  water  from  3*2°  to  172°,  or  140°. 

This  may  be  proved 
by  the  following  ex- 
periment: Fig.  52. 
Let  a  pound  ot  brok- 
en ice  at  32°,  and  a 
pound  of  water  tilso 
at  32°,  be  introduced 
into  two  separate 
glass  jars,  of  the 
same  size  and  thick- 
ness, and  in  every 
respect  exactly  alike, 
and  let  both  be  placed 
in  a  shallow  metal. ic 
pan,  filled  to  the 
depth  of  an  inch 
with  water.  Let  a  thermometer  be  placed  in  each  jar,  not  ar- 
ranged as  in  the  figure,  with  its  bulb  touching  the  bottom,  but 
su-pended  so  that  each  bulb  just  dips  beneath  the  surface  of 
the  broken  ico  and  of  the  water.  Each  thermometer  will  stand, 
of  course,  at  32°.  Now  let  a  lamp  be  placed  beneath  the  metal- 

What  has  become  of  the  heat  absorbed,  and  how  has  it  been  expended? — 141.  How 
pouch;  heat  is  absorbed  in  the  melting  of  ice  ?  Describe  the  experiment  by  which  this 
Amount  is  determined. 


Amount  of  Htat  absorbed  in  Liquefaction, 


THE    HEAT    OF    FLUIDITY.  Il5 

lie  pan,  and  the  water  conta:ned  in  it  be  slowly  heated.  Both 
jars  receive  heat  at  the  same  rate,  and  we  should  suppose 
that  the  thermometers  would  indicate  a  temperature  increasing 
at  the  same  rate  in  both ;  but  instead  of  this,  they  a"6  found  to 
be  very  unequally  affected.  The  thermometer  in  the  jar  con- 
taining water  at  32°  immediately  begins  to  rise,  while  that  in 
the  jar  containing  ice  at  32°  remains  stationary,  and  does  not 
begin  to  rise  until  the  ice  is  entirely  melted.  If  at  the  instant 
when  the  last  particle  of  ice  disappears  and  while  its  tempera- 
ture is  still  at  32°,  we  observe  the  thermometer  in  the  jar  con- 
taining water,  it- will  be  found  to  have  risen  from  32°  to  172°, 
showing  that  the  water  has  received  140°  of  heat.  The  ice  in 
the  other  jar  has  necessarily  received  precisely  the  same  amount, 
yet  its  temperature  remains  unaffected.  What  has  become  of 
this  140°  of  heat?  It  has  obviously  been  absorbed  in  causing 
the  ice  to  liquefy,  and  in  so  doing  has  become  insensible  to  the 
thermometer.  As  soon  as  the  ice  has  entirely  melted,  the  ther- 
mometer will  begin  to  rise,  just  as  it  d'.d  in  the  jar  containing 
water,  because  tli3  heat  received  from  the  lamp  is  no  longer  ex- 
pended in  producing  the  change  from  the  solid  to  the  liquid 
state,  and  exerts  the  ordinary  effects  of  heat  of  temperature. 

142.  The  amount  of  Heat  absorbed  in  the  Liquefaction  of 
Ice  shown  by  a  second  experiment.    If  a  pound  of  water  at  32° 
be  mixed  with  a  pound  of  water  at  172°,  the  temperature  of  the 
mixture  will  be  intermediate  between  them,  or  102°, — the  mean 
tsmperature.     But  if  a  pound  of  water  at  172°  be  added  to  a 
pound  of  ice    at   32°,  the    ice   will   quickly  dissolve,  and  on 
placing  a  thermometer  in  the  mixture  it  will  be  found  to  stand 
not  at  102°,  but  at  32°.     In  this  experiment  the  pound  of  hot 
water  which  was  originally  at  172°,  actually  kres  140°  of  heat,  all 
of  which  enters  the  ice  and  causes  its  liquefaction,  but  without 
affecting  its  temperature ;  whence  it  follows  that  a  quantity  of 
heat  becomes  insensible  during  the  melting  of  ice  sufficient  to 
raise  the  temperature  of  an  equal  weight  of  water  by  140°  F. 
This  explains  the  well  known  fact  on  which  the  graduation  of 
the  thermometer  depends,  that  the  temperature  of  melting  ice 
or  snow  never  exceeds  32°  F.     All  the  heat  which  is  added  be- 
comes insensible  until  the  liquefaction  is  complete. 

143.  Heat  of  Fluidity,     The  heat   thus  absorbed    in    the 
liquefaction  of  solids  is  called  the  heat  of  fluidi  y,  and  is  essen- 

142    Describe  a  second  experiment  by  which  the  same  fict  may  be  proved.     Why  can 
not  meltinsr  ice  rise  above  32°  until  the  whole  id  melted  ?— 113,  Wh^t  id  meant  by 
beat  of  fluidity  ? 


116         TEMPERATURE    LIMITED    BY    POINT    OF   FUSION. 

tial  to  the  existence  of  the  substance  in  the  liquid  state.  It 
varies  very  much  in  different  bodies.  In  ice,  as  we  have  seen, 
the  amount  of  heat  absorbed  is  140°;  in  beeswax  it  is  175°;  in 
lead  162°;  zinc  493°;  tin  500°;  bismuth  550°;  all  of  which  is  in 
each  case  given  out  when  the  body  returns  to  the  solid  state. 
The  heat  in  all  these  instances  is  not  lost,  but  is  simply  rendered 
insensible  to  the  thermometer.  It  enters  into  the  constitution 
of  the  substance  in  question  without  raising  its  temperature. 
When  the  process  is  reversed,  and  the  substance  is  reconverted 
into  a  solid,  the  heat  which  has  been  rendered  insensible  is  again 
given  out,  and  tli3  temperature  of  the  body  rises.  Consequently, 
whenever  a  eolid  is  converted  into  a  liquid,  there  is  an  immense 
absorption  of  heat,  accompanied  by  a  diminution  of  temperature  ; 
whenever  a  liquid  is  changed  into  a  solid,  there  is  an  immense 
evolution  of  heat,  accompanied  by  an  increase  of  temperature. 
Similar  variations  in  temperature  are  effected  by  simple  change 
of  density,  without  any  such  change  in  state  as  to  produce  either 
liquefaction  or  solidification.  Condense  any  substance,  and  its 
temperature  rises ;  expand  it,  arid  its  temperature  sinks. 

144.  Solid  substances  undergoing  liquefaction  can  never 
be  heated  above  their  point  of  fusion,  until  the  whole  of  the 
Solid  is  melted.  When  a  solid  is  undergoing  liquefaction,  all 
the  heat  that  enters  it,  is  expended  in  producing  the  change  of 
state,  and  none  of  it  goes  to  raise  the  temperature  until  every 
particle  of  the  solid  has  melted.  Thus  we  have  seen  in  the 
case  of  melting  ice,  that  the  temperature  of  the  ice  can  not  be 
raised  above  32°  until  the  last  particle  of  the  solid  has  disap- 
peared. In  the  Fame  way,  if  a  mass  of  tin  have  its  tempera- 
ture raised  to  442°  it  will  then  begin  to  melt,  and  its  tempera- 
ture can  be  raised  no  higher  until  the  last  particle  of  tin  be 
melted,  after  which  the  temperature  will  rise  as  usual.  In 
like  manner  lead  will  begin  to  liquefy  at  594°,  and  notwith- 
standing the  constant  addition  of  heat,  its  temperature  will  not 
rise  above  594°  until  its  fusion  is  complete.  The  same  is  true 
of  beeswax ;  it  can  not  be  raised  above  its  melting  point,  how- 
ever great  the  heat  applied,  so  long  as  any  wax  remains  un- 
melted ;  and  even  in  the  case  of  iron,  which  melts  at  2786°, 
notwithstanding  the  intense  heat  of  the  furnace,  it  can  not  be 
raised  above  this  point  so  long  as  any  solid  iron  remains,  because 

Is  it  the  same  in  amount  for  all  bodies  ?  What  is  the  effect  of  liquefaction  upon  sur- 
.rounding  temperature?  What  is  the  effect  of  solidification  upon  temperature?  What 
is  the  effect  of  change  of  density  upon  temperature? — \ty.  Wb,y  can  not  soijds  under- 
going liquefaction  bo  heated  above  the  melting  point  ? 


SOLIDIFICATION    ELEVATES    TEMPERATURE. 


117 


all  the  heat  that  enters  it,  however  great,  is  entirely  expended 
in  producing  liquefaction,  and  none  at  all  goes  towards  the  ele- 
vation of  temperature. 

145.  The  Heat  absorbed  in  Liquefaction  given  out  in  So- 
lidification. The  heat  thus  absorbed  in  liquefaction  is  given  out 
and  rendered  sensible  again  when  the  liquid  returns  to  a  solid  state. 
This  may  be  shown  by  immersing  a  ves- 


Fig.  53. 


sel  of  water  at  60°,  containing  a  ther- 


Heat  of  Liqitf  faction  given  out 
in  Solidification. 


mometer,  in  a  freezing  mixture  of  ice 
and  salt,  at  0°.  The  thermometer  will 
immediately  sink,  and  continue  to  do 
so,  until  it  reaches  32°,  when  it  will 
suddenly  stop ;  and  though  the  freezing 
mixture  is  at  0°,  the  water  in  the  vessel 
persists  in  remaining  at  32°,  and  at  the 
same  time  slowly  freezes.  It  loses 
heat  at  the  same  rate  after  it  reached 
32°  as  it  did  before  ;  why  does  not  its 
temperature  sink  ?  manifestly  because 
thy  water  in  freezing  is  giving  out  the 
140°  of  heat  which  it  had  absorbed  in 
liquefying,  and  this  it  is  which  keeps 
up  its  temperature :  Fig.  53.  The  same  fact  may  be  proved  by 
another  experiment  If  water  be  kept  undisturbed  it  may  be 
cooled  to  12°  or  20°  below  its  freezing  point,  32°,  without  congeal- 
ing, but  upon  the  least  agitation  a  small  portion  is  made  to  solidify, 
an  1  the  heat  given  forth  by  this  small  portion  in  passing  from 
the  liquid  to  the  solid  state,  is  sufficient  to  raise  the  temperature 
of  the  whole  mass  of  the  water  from  12°  to  32°.  Melted  phos- 
phorus, acetic  acid,  and  sulphuric  acid,  also  admit  of  being  cooled 
down  several  degrees  below  their  points  of  solidification,  but  if-" 
touched  or  agitafed  they  immediately  solidify  with  the  evolution 
of  heat.  The  solidification  of  metallic  bodies  is  attended  with 
like  results ;  a  liquid  a]loy  of  potassium  and  sodium  may  be 
formed  by  pressing  together  the  two  metals,  which  at  common 
temperatures  are  quite  soft;  if  a  drop  of  mercury  be  added  to 
thym  they  instantly  solidify,  and  in  doina;  so  emit  heat  enough  to 
set  fire  to  the  naphtha  which  is  used  to  protect  them  from  the  air. 
The  freezing  of  water,  and  solidification  in  general,  under  all  cir- 
cumstances, strange  as  it  may  appear,  is  attended  with  the  evo- 


145.  Show  that  the  heat  absorbed  in  liquefaction  is  given  out  again  in  solidification. 
Explain  the  rise  of  temperature  in  water  at  12o,  when  it  is  frozen.  Explain  the  combus- 
tion produced  when  an  alloy  of  sodium  and  potassium  is  mixed  with  mercury. 


.LIQUEFACTION    LOWERS    TEMPERATURE. 


lution  of  heat,  and  is  a  warming  pro- 
cess. When  a  pound  of  water  is  frozen, 
sufficient  heat  is  given  out  to  raise  an- 
other pound  of  water  from  32°  to  172°, 
and  to  impart  to  it  1 40°  of  heat* 
If  a  ton  of  water  be  frozen,  the  same 
fact  is  true ;  the  heat  given  out  is  suf- 
ficient to  raise  another  •  ton  of  water 
from  32°  to  172°,  or  to  heat  140  tons 
of  water  1°.  A  similar  extrication 
of  heat  occurs  in  a  1  cases  of  solidi- 
fication. The  precipitation  of  mat- 
ter in  a  solid  form  from  a  state  of 
solution  always  produces  heat.  Make 
a  saturated  solution  of  sulphate  of  soda, 
or  Glaubers  salt,  in  warm  water  at  90°, 
and  set  it  aside  until  it  cools,  having 
first  tightly  corked  it ;  on  shaking  the 
bottle,  the  solution  will  sudden^  crys- 
tallize, and  its  temperature  rise  sevr 
eral  degrees,  as  shown  by  the  ther- 
mometer. If  we  piepare  a  saturated 
solution  of  acetate  of  soda  in  boiiing 
water  and  allow  it  to  cool  without  agi- 
tation, on  pouring  it  over  a  bulb,  the 
beak  of  which  is  dipped  beneath  the 
surface  of  water  in  a  bowl,  it  will  im- 
mediately solidify,  and  in  so  doing  give 
out  heat  enough  to  drive  out  a  part 
of  the  air,  in  bubbles  through  the  water.  See  Fig.  54,  where  the 
water  occupies  a  portion  of  the  stem,  and  descends  rapidly  on 
the  application  of  the  solution. 

146.  Liquefaction,  by  whatever  cause  produced,  always 
attended  by  a  Reduction  of  Temperature.  Liquefaction  pro- 
duces cold.  This  is  not  only  true  wrhen  solids  are  melted  by  the 
application  of  heat,  but  in  every  case  in  which  solid  matter  is 
liquefied,  by  whatever  means.  Liquefaction  can  not  take  place 
without  the  absorption  of  a  large  amount  of  heat ;  consequently, 
if  we  can  effect  or  compel  liquefaction  without  the  direct 
application  of  heat,  a  strong  demand  for  heat  is  at  once  created, 
which  must  be  satisfied  at  the  expense  of  the  heat  of  surrourid- 


Heat  produced  by  Suddijica- 
tion. 


146.  Why  is  liquefaction,  by  whatever  cause  produced,  always  attended  by  a  reduction 
Of  temperature  ? 


FREEZING    MIXTURES.  119 

ing  bodies,  and  their  temperature  consequently  sinks.  Now  we 
have  the  means  of  causing  bodies  to  liquefy  suddenly  by  chemi- 
cal means,  without  the  application  of  heat ;  and  consequently  of 
producing  a  diminution  of  temperature  in  surrounding  objects, 
by  the  demand  for  heat  which  is  thus  created. 

147.  Freezing-  fixtures.  On  this  principle  depends  the 
operation  of  what  are  called  freezing  mixtures.  One  of  the 
simplest  of  these  is  composed  of  ice  and  salt.  Wtan  mixed, 
these  two  solids  combine  in  such  a  way  that  both  are  liquefied, 
heat  is  absorbed,  surrounding  temperature  sinks,  and  the  ther- 
mometer speedily  falls  to — -4°,  or  36°  below  the  freezing  point 
of  water.  Care  should  be  taken  that  no  heat  be  furnished 
either  by  the  vessel  in  which  the  liquefaction  takes  place, 
or  from  any  other  external  source.  It  follows,  therefore,  that 
the  heat  which  is  ab  orbed  must  be  supplied  by  the  substances 
themselves  which  compose  the  mixture,  and  which  must  .suffer 
a  diminution  of  temperature  proportioned  to  the  quantity  of 
heat  thus  rendered  latent.  The  cold  produced  will  be  increased, 
by  reducing  the  temperature  of  the  substances  in  question,  be- 
fore mixing  them.  The  vessel  in  which  the  mixture  is  made 
should  be  placed  in  a  larger  vessel,  also  containing  some  of  the 
freezing  mixture,  for  the  purpose  of  cutting  off  every  supply  of 
heat  to  the  inner  vessel  from  the  outside.  The  solids  employed 
must  be  pulverized  so  as  to  dissolve  quickly  ,  and  if  salts, 
must  not  have  lost  their  water  of  crystallization,  or  have  become 
anhydrous.  There  are  freezing  mixtures  more  effective  than 
ice  and  salt.  Thus,  chlorohydric  acid  5  parts  by  weight,  and 
snow  or  ice,  8  parts,  will  sink  the  temperature  from  32°  to  —  21°. 
A-;ain,  if  equal  weights  of  snow  and  common  salt,  at  323,  be 
mixed,  they  will  liquefy,  an  I  the  temperature  will  fall  to  —  9°. 
If  2  Ibs.  of  chloride  of  calcium,  and  1  Ib.  of  snow,  be  separately 
reduced  to  —  9°  in  this  liquid,  and  then  mixed,  they  will  liquefy, 
and  the  temperature  will  fall  to  —  74°.  If  4  Ibs.  of  snow,  and 
5  Ib*.  of  sulphuric  acid,  be  reduced  to  —  74°  in  this  last  mix- 
ture, and  then  mixed,  they  will  liquefy,  and  the  temperature 
will  fa  1  to  —  90°.  Again,  if  1  lb.  of  snow  be  dissolved  in 
about  2  quarts  of  alcohol,  the  mixture  will  fall  nearly  to — 13°. 
If  the  same  quantities  of  snow  and  alcohol,  after  being  reduced  in 
this  mixture  to. — 13°,  be  then  mingled,  the  temperature  of  the 
mixture  will  be  reduced  to  —  58°,  and  the  same  process  being 

147.  What  are  freezing  mixtures  ?    Explain  the  principle  on  which  they  depend.     Give 
some  of  the  most  important  freezing  mixtures. 


120  THE    FREEZING    OF    SALT    WATER. 

% 

repeated,  with  like  quantities  in  this  second  mixture,  a  further 
reduction  of  temperature  to  —  98°  may  be  effected,  and  so  on. 
The  lowest  known  temperature?,  however,  have  been  produced 
by  liquefying,  and  then  evaporating  some  of  the  gases.  Tem- 
peratures have  been  thus  produced,  varying  from —  120°  F.  to 
—  220°.  At  such  temperatures,  mercury,  which  freezes  at  — 
40°  F.,  is  easily  solidih'ed,  and  it  is  said  that  even  al;  ohol,  a 
liquid  which  has  hitherto  resisted  all  attempts  at  solidificat'on, 
has  been  reduced  to  the  consistency  of  oil  and  melted  wax. 
These  processes  will  be  described  hereafter.  The  extreme  cold 
thus  produced  will  perhaps  be  better  understood  by  comparison 
with  some  of  the  lowest  natural  temperatures.  The  severest 
natural  cold  ever  noted  was  in  Siberia,  lat.  55  N.,  where  the 
thermometer  was  observed  to  indicate — 91 ,75°  F.  At  Jakerlsh, 
the  mean  temperature  of  the  month  of  December  is  —  44^°  F., 
and  it  has  been  known  as  low  as  —  58°.  In  the  expedition  in 
Khiva,  in  December,  18o9,  the  Russian  army  experienced  for 
several  successive  days  a  temperature  of — 41.8°  F. 

148.  3. he  solution  of  Salts  and  Acids  in  Walcr  lowers  its 
Freezing1  Point.  The  freezing  points  of  liquids  «re  generally 
lowered  when  salts  are  dissolved  in  them.  The  freezing  point 
of  pure  water  is  stationary  at  32° ;  but  sea  water,  which  con- 
tains several  different  salts  dissolved  in  it,  chiefly  common  Fait, 
freezes  at  27.4°  F.,  the  salt  separating,  and  the  pure  water  float- 
ing in  the  form  of  ice ;  whilst  water  which  is  saturated  with  sea 
salt  sinks  as  low  as  —  4°  F.  before  freezing.  In  like  manner 
the  strong  acid:*,  like  the  sulphuric  acid,  and  the  nitric,  will  very 
considerably  reduce  the  freezing  point  of  the  water  with  which 
they  are  mixed.  The  icebergs,  therefore,  which  float  in  the  sea, 
and  all  the  ice  formed  in  the  ocean  in  winter,  consist  of  per- 
fectly pure  water.  In  like  manner,  if  \vater  hold  in  solution  a 
small  quantity  of  alcohol,  and  be  frozen,  the  ice  will  be  found  to 
contain  no  admixture  of  alcohol,  but  to  fce  the  ice  of  perfectly 
pure  water.  This  method  is  sometimes  practiced  to  give  in- 
creased strength  to  weak  wines,  for,  as  the  wrater  freezes,  the 
remaining  liquid  becomes  proportionally  stronger.  In  the  pro- 
cess of  freezing,  as  it  goes  on  in  Nature,  solidification  does  not 
proceed  continuously,  but  the  ice  is  formed  in  successive  layers, 
and  in  the  intervals  between  these  layers  is  a  stratum  of  ice, 
slightly  more  fusible  than  the  mass  either  above  or  below. 

148.  What  is  the  effect  upon  the  freezing  point  of  water  of  dissolving  salts  in  it  1  What 
effect  has  the  mixing  of  acids  with  water  upon  its  freezing  point?  What  is  the  effect 
of  freezing  upon  salt  water  1  What  is  the  effect  of  freezing  upon  water  containing  alco^ 
hoi  in  solution? 


FLUXES.  121 

149.  Sometimes  two  different  substances  mixed,  fuse  at  a 
temperature    much    lower    than   either   separately. — Fluxes. 

Salt  may  be  said  to  be  a  flux  for  ice,  because  it  tends  to  liquefy 
the  ice  without  the  application  of  heat,  at  a  lower  temperature 
than  it  would  melt  without;  in  the  same  manner  other  sub- 
stances, when  mixed,  often  tend  to  fuse  at  a  temperature  much 
lower  than  the  fusing  point  of  either  separately.  In  this  way 
many  very  infusible  substances  are  melted  by  mingling  with 
them  other  bodies  with  which  they  tend  to  unite.  Silica,  the 
mo>t  important  constituent  in  glass,  is  not  fusible  by  any  heat 
of  the  most  powerful  wind  furnace,  but  if  soda,  potash,  lime, 
and  lead,  be  mixed  with  it,  fusion  takes  place  very  readily  at  a 
comparatively  low  temperature.  These  substances  are  hence 
called  Jinxes.  In  the  manufacture  of  porcelain,  fluxes  are  em- 
ployed;  and  also  in  the  reduction  of  the  metals  from  their  ores. 
For  this  reason  iron  ore  is  always  mixed  with  lime  before  it  is 
subjected  to  the  action  of  the  blast  furnace.  In  the  case  of 
some  of  the  salts,  the  lowering  of  the  point  of  fusion  is  very 
extraordinary ;  thus  nitrate  of  potash  melts  at  642°  F.,  the  ni- 
trate of  soda  at  591°  F. ;  but  a  mixture  of  the  two,  in  equiva- 
lent proportions,  liquefies  as  low  as  429°,  or  162°  below  the 
melting  point  of  the  most  fusible  of  the  two  salts.  In  like 
manner  some  of  the  alloys  of  different  metals  will  often  melt  at 
much  lower  temperatures  than  any  of  the  metals  employed  sepa- 
rately. An  alloy  of  8  parts  of  bismuth,  5  of  lead,  and  o  of  tin, 
m?lts  at  a  temperature  below  that  of  boiling  water,  and  an  alloy 
of  496  parts  of  bismuth,  310  lead,  177  tin,  and  26  mercury, 
fu^es  at  162.5°  F.  If  a  thin  strip  of  this  alloy  be  dipped  in!o 
water  that  is  nearly  boiling  hot,  it  will  melt  like  \vax.  Some 
bodies,  like  water,  pass  at  once  from  the  complete  solid  to  the 
complete  liquid  state  without  passing  through  any  intermediate 
condition ;  while  others,  like  wax,  tallow,  and  phosphorus,  be- 
come soft  at  temperatures  much  lower  than  those  at  which  they 
are  liquefied ;  and  there  are  others,  like  glass  and  platinum, 
which  never,  under  any  circumstances,  attain  absolute  fluidity. 

150.  Refractory  substances.     Bodies,    whose  fusion  is  ex- 
ceedingly    difficult,    or     which  resist  it  altogether,  are  called 
refractory.     No    substance    can   be  said   to    be  absolutely  in- 
fusible, except  carbon,  which,  under  all  its  forms,  of  pure  carbon, 

149  What  are  fluxes?  How  may  salt  be  said  to  be  a  flux  for  ice?  Describe  the  use 
of  fluxes  in  the  making  of  glass  and  porcei  an.  What  is  the  use  of  the  lime  employed 
in  the  smelting  of  iron?  How  does  the  melting  point  of  alloys  compare  with  that  of  the 
metals  which  enter  into  them  ?— 150.  What  are  refractory  substances  ? 

6 


122  IMPORTANT    RESULTS 

charcoal,  anthracite,  graphite,  and  diamond,  has  resisted  fusion 
at  the  highest  temperature  which  has  yet  been  produced.  There 
i  .  reason  to  believe  that  even  carbon  may  yet  be  fused  by  long  sub- 
jection to  the  intense  heat  of  Ruhmkorff's  coil ;  §  405.  Of  the 
metals,  platinum  is  the  most  infusible,  and  it  can  not  be  melted 
except  by  the  oxyhydrogen  blow-pipe,  an  instrument  to  be 
described  hereafter,  and  by  the  galvanic  current.  Wrought 
iron  is  also  extremely  difficult  of  fusion.  Among  the  most  re- 
fractory bodies  are  the  earths, — lime,  alumina,  baryta,  strontin. 
Some  compound  substances  can  not  be  melted,  because  decom- 
position takes  place  before  the  degree  of  heat  necessary  ior 
fusion  has  been  attained.  Thus  marble,  ordinarily,  can  not  be 
melted,  because,  at  a  red  heat,  it  is  decomposed,  and  one  of  Its 
constituents,  the  carbonic  acid  gas,  escapes ;  but  if  it  be  tightly 
confined  in  a  strong  gun-barrel,  so  that  nothing  can  escape,  and 
intense  heat  be  applied,  its  fusion  can  be  accomplished. 

151.  Facility  of  liquefaction  proportioned  to  the  quantity 
of  lament  heat  required.     The  different  degrees  of  facility  with 
which  bodies  are  liquefied  depends  in  part  upon  the  relative 
amounts  of  heat  which  are  rendered  latent  in  the  process.     Thus 
ice  liquefies  very  slowly,  because  the  latent  heat  required  is  very 
great,  water  containing  more  latent  heat,  or  heat  of  composition, 
than  any  other  known  substance.     Phosphorus  and  lead,  on  the 
other  hand,  whose  latent  heat  is  small,  melt  very  easily ;  ice  can 
not  be  liquefied  until  it  has  received  sufficient  heat  to  raise  an 
equal  weight  of  water  140°,  while  lead  and  phosphorus  are 
melted  by  as  much  heat  as  would  raise  their  own  weight  of 
water  by  9°.     If  but  little  heat  is  absorbed,  and  becomes  latent, 
all  the  heat  that  enters  the  body  in  question  goes  at  once  towards 
its  liquefaction ;  whereas,  if  a  large  quantity  becomes  latent,  it 
i.3  obvious  that  but  a  small  amount  can  go  towards  the  liquefac- 
tion, and  the  rapidity  of  that  process  is  proportionably  retarded. 

152.  The  important  results  of  the  absorption  of  Heat  in 
Liquefaction,  and  its  evolution  in  Solidification.     The  absorp- 
tion of  this  large  amount  of  heat  in  liquefaction,  and  the  pro- 
portional evolution  of  heat  in  solidification,  lead  to  two  most 
important  results:     1st.  The  solidification  of  large  bodies  of 
water  sets  free  an  amount  of  heat  previously  latent  in  the  water 
which  is  of  the  greatest  value  in  mitigating  the  rigors  of  a  cold 

Which  is  the  most  infusible  of  all  known  substances  ?  Which  is  the  most  infusible  of 
the  metals? — 151.  To  what  is  the  facility  of  liquefaction  proportioned?  Give  illustra- 
tions of  this  in  the  case  of  water  and  phosphorus. — 152.  What  important  results  How 
from  tlie  absorption  and  evolution  of  heat  in  liquefaction  and  solidification  ? 


OF    THESE    LAWS.  123 

climate.  The  act  of  freezing  liberates  heat,  and  very  percepti- 
bly moderates  the  temperature  of  the  atmosphere.  As  soon  as 
ice  begins  to  form  upon  the  surface  of  a  lake  in  winter,  the 
tempera* ure  of  the  atmosphere  is  immediately  elevated.  In 
the  severest  weather  of  winter,  if  a  snow  storm  occur,  the  air 
at  once  becomes  warmer  from  the  heat,  previously  latent  in  the 
watery  vapor,  now  given  forth  by  its  condensation  and  solidifi- 
cation. For  the  same  reason  water  is  often  placed  in  cellars 
for  the  purpose  of  preventing  frost  by  the  heat  given  forth  by 
its  own  congelation.  2d.  The  large  amount  of  heat  required 
for  liquefaction  tends  to  make  the  melting  of  solids  s'ow 
and  gradual,  and  the  large  amount  of  heat  given  forth  in  solidi- 
fication tends  to  make  the  congelation  of  liquids  equally  slo.v 
and  gradual.  A  check  is  thus  placed  upon  the  rapidity  of  both 
these  processes,  and  matter  is  prevented  from  suddenly  passing 
from  one  state  to  the  other  in  either  direction.  We  see  the  im- 
portance of  this  pro  vis  on  in  the  impediment  which  is  thus 
placed  in  the  way  of  the  sudden  liquefaction  of  large  masses  of 
snow  and  ice  in  the  spring;  if  it  were  not  for  the  immense 
amount  of  heat  required,  and  which  can  not  readily  be  obtained, 
the  ice  and  snow  that  had  accumulated  during  a  long  winter 
would,  at  the  first  approach  of  mild  weather,  be  at  once  con- 
verted into  water,  and  sweep  away  not  only  the  works  of  man, 
but  also  those  of  Nature  herself, — the  trees,  rocks,  and  hills. 
The  difficulty  of  suddenly  supplying  so  vast  an  amount  of  heat 
necessarily  makes  the  process  of  melting  very  gradual.  What 
would  be  the  consequences  if  there  were  no  sueli  provision  can 
be  imagined  from  the  destructive  effects  that  are  produced  in 
s  >ite  of  it,  by  the  melting  of  ice  and  snow  in  the  spring;  if  the 
vast  body  of  water  which  is  produced  were  formed  in  the  course 
of  a  single  day,  it  is  evident  that  every  thing  would  be  swept 
before  it.  Occasion  illy  catastrophes  of  this  kind  do  occur,  when 
a  volcano,  su  -h  as  Etna,  pours  forth  a  stream  of  lava  over  fields 
of  ice  and  snow ;  tlje  des  ruction  which  is  produced  by  the  tor- 
rents of  water  is  even  greater  than  that  of  the  lava  itself.  As 
we  advance  towards  the  north  the  transition  from  winter  to 
summer  is  very  rapid,  taking  place  almo-t  in  a  day,  and  it  is 
evident  tint  the  beneficial  results  of  this  constitution  of  matter 
in  countries  where  the  masses  of  snow  and  ice  accumulated  in 
winter  are  immense,  must  be  altogether  incalculable.  Again, 

Wh:it  elect  is  pnvlure-1  upon  the  temperature  of  the  air  by  the  freezing  of  water  in  fie 
autumn?  U'h  it  eTeet  is  pro.luee  1  u;>o;i  the  mpitlity  of  the  melting  of  suow  in  tiio 
spring  by  tlie  absorption  of  *o  large  au  amouut  of  heat  ? 


124  DISCOVERED    BY    DR.    BLACK. 

when  in  the  autumn  large  masses  of  water  are  frozen,  the  heat 
latent  in  the  liquid,  and  essential  to  its  liquidity,  is  given  forth, 
and  this  has  the  effect  of  elevating  the  temperature  of  the  re- 
maining water,  and  also  of  warming  the  atmosphere  in  contact 
with  it.  The  evolution  of  this  large  amount  of  heat  has  the 
effect  of  retarding  the  freezing  process,  and  limiting  its  effects. 
An  impediment  is  thus  placed  in  the  way  of  the  sudden  freez- 
ing of  large  bodies  of  water.  So  happily  adjusted  are  all  the 
arrangements  of  Nature  to  subserve  the  comfort  of  man,  and 
the  preservation  of  animal  and  vegetable  life. 

153.  The  beneficial  effects  of  all  the  laws  of  Nature,  and 
of  their  exceptions  in  special  cases.    All  animal  and  vegetable 
life  depends  upon  the  preservation  in  a  permanently  liquid  state 
of  vast  quantities  of  water.     To  secure  this  end,  the  freezing 
of  water  is  made  a  slow  process,  by  the  latent  heat  which  u 
given  forth  as  eoon  as  it  begins  to  take  place.     A  similar  pro- 
vision, as  we  shall  see,  prevents  it  from  too  rapidly  evaporating. 
Both  these  arrangements  show  the  wisdom,  power  and  benefi- 
cence of  the  Most  High  most  emphatically  and  plainly,  as  in- 
deed do  all  the  laws  to  which  he  has  subjected  the  world  of 
matter.     But  especially  arc  these  attributes  shown  in  the  ex- 
ceptions which  he  has  made  to  his  own  laws,  when  their  regular 
operation  would  be  injurious  to  the  welfare  of  man.     These 
display  a  very  peculiar  and  refined  design  which  demands  our 
highest  admiration ;  and  perhaps  the  most  striking  of  the  e  ex- 
ceptions is  shown  in  the  exemption  of  water  from  the  ordinary 
law  of  expansion  and  contraction,  when  its  execution  would  be 
injurious  to  man.     When  water  has  cooled  to  a  certain  point, 
the  ordinary  law  is  reversed,  the  warm  water  sinks,  and  the 
cold  water  floats  upon  the  surface.     In  what  powerful  language 
does  this  single  fact  in  Nature  speak  to  every  religious  mind ! 

154.  The  discoverer  of  the  laws  of  Latent  Zlcat.     It  is  to 
the  celebrated  Dr.  Joseph  Black,  Prof,  of  Chemistry  in  the 
University  of  Edinburgh,  that  we  are  indebted  for  the  greater 
part  of  our  knowledge  on  this  subject.     It  is  stated  that  an 
observation  of  Fahrenheit,  recorded  by  the  celebrated  Boer- 
haave,  "  that  water  would  become  considerably  colder  than  melt- 
ing snow  without  freezing,  and  would  freeze  in  a  moment,  if 
disturbed,  and  in  the  act  of  freezing  emit  many  degrees  of  heat," 

153.  How  is  the  permanently  liquid  state  of  large  amounts  of  water  secured  ?  What 
speci.-.l  design  is  shown  by  the  peculiar  constitution  of  water  and  its  exception  at  cer- 
tain temperatures,  to  the  law  of  expansion  from  heat. — 154.  Who  was  tho  discoverer  of 
tiie  laws  of  latent  heat?  What  directed  his  attention  to  the  subject? 


EXPERIMENTS    ON  125 

first  suggested  to  Dr.  Black  the  idea  that  the  heat  received  by 
ice  during  its  conversion  into  water  is  not  lost,  but  is  contained 
in  the  water.  He  instituted  a  careful  train  of  experiments 
which  fully  established  the  immense  absorption  of  heat  in  lique- 
faction and  vaporization,  and  its  corresponding  evolution  in  con- 
densation and  solidification.  These  experiments  may  be  fo:ind 
fully  detailed  in  his  own  words,  in  his  Lectures,  one  of  the  most 
instructive  and  interesting  works  on  chemistry  to  be  found  in 
our  language.  This  discovery  of  Dr.  Black  unfolded  the  true 
theory  of  the  steam  engine,  and  suggested  to  Mr.  Watt  many 
of  his  most  important  improvements. 

Experiments:    Effects  of  Heat.— Liquefaction. 

1.  Liquefaction.     That  heat  produces  liquefaction  may  be  shown  by  heating  ice, 
lead,  or  any  other  solid  easily  fusible. 

2.  That  liquefaction  is  accompanied  by  the  disappearance  of  a  large  amount  of  heat 
may  be  shown  by  heating  a  cup  tilled  witii  ice  at  0°,  and  containing  a  thermometer,  over 
a  lamp.     Tiie  thermometer  wiil  rise  to  32°  and  then  remain  stationary  until  till  the  ice 
has  melted,  notwithstanding  it  has  been  receiving  heat  at  the  same  rate  all  the  time. 
Wh  it  h  is  become  of  i:  ?    Evidently  it  has  been  absorbed.     The  ice  may  be  reduced  to  0" 
by  immersion  in  a  freezing  mixture  of  ice  and  salt. 

J.  The  same  fact  is  shown  by  dissolving  common  salt,  nitrate  of  potash,  nitrate  of 
ammonia,  chloride  of  calcium,  and  in  general  all  the  salts,  in  water,  and  noting  the  great 
diminution  of  temper  iture  which  results,  as  tested  by  the  thermometer. 

4  Take  207  parts  or  lead,  118  of  tin,  284  of  bismuth,  melt  them  together  in  a  crucible, 
and  Ti'ducj  them  to  a  finely  divided  state  by  throwing  into  cold  water.  On  dissolving 
thi;  a.loy  in  1;U7  parts  of  mercury,  the  thermometer  will  sink  from  64°  F.  to  14°,  and 
water  may  be  fro/.ea  by  tiie  process. 

5.  The  amount  of  heat  absorbed  in  the  melting  of  ice  may  be  shown  to  be  what 
would  heat  an  equal  weight  of  water  140°,  by  pouring  a  pound  cf  water  at  172°  upon  a 
piund  of  ice  at  32J.     The  ice  will  be  melted  by  the  heat  of  the  hot  water,  but  the  tern. 
pLT.it  are  of  the  whole  mixture  at  the  conclusion  of  the  experiment  will  be  only  32°,  i.  e., 
14  i°  of  neat  will  h  ive  disappeared  and  been  absorbed. 

6.  The  same  f  .ct  is  shown  by  the  experiment  described  on  page  114.     Two  glass  beak- 
er:, one  containing  a  pound  of  ice  at  32°,  the  other  a  pound  of  v/ater  at  32°,  each  having 
a  thermometer  suspended  in  it,  with  the  bulb  a  little  distance  below  the  surface,    are 
place  1  in  a  shallo.v  tin  pan  kept  boiling  by  a  lamp.     They  receive  heat  at  the  same  rate, 
and  the  temperature  of  the  water  rises,  while  that  of  the  ire  remains  stationary  at  32°1 
By  the  time  the  water  has  reached  172°,  or  received  140°  of  heat,  the  ice,  which  has  re- 
ceived just  as  much,  will  only  have  melted,  and  the  temperature  of  the  vessel  containing 
it  will  still  be  only  32°.     See'Fig.  52. 

7.  Solid  ideation   produces   Heat.     Potassium  and  Sodium  pressed  together 
in  a  mortar  produce  a   liquid  alloy;   add  mercury,  and  this  liquid  becomes  a  solid, 
and  heat  enough  is  set  f:-ee  to  inflame  the  naphtha  adhering  to  the  potassium. 

8.  To  a  strong  solution  of  chloride  of  calcium  or  muriate  of  lime,  add  a  drop  or  two 
of  sulphuric  acid ;  a  solid  results,  and  much  heat  is  produced. 

9.  \Vater  and  quirk  lime  mixed,  solidify  with  the  production  of  much  heat.     If  phos- 
phorus in  a  watch  glass  be  placed  upon  the  mixture  it  will  be  inflamed,  and  water  in  a 
test  tube  may  be  boiled. 

1 0  L'lace  a,  small  jar  of  water  at  60°  or  70°.  and  containing  a  thermometer,  within 
'  a  larger  jar,  and  let  the  space  between  them  be  filled  with  a  freezing  mixture  of  snow 
and  salt  at  a  temperature  of  0°,  as  shown  by  a  second  thermometer.  The  water  in. 
the  inner  vessel  will  steadily  sink  in  temperature,  until  its  thermometer  indicates  32°, 
but  at  this  degree  it  will  remain  stationary,  though  the  mixture  around  it  is  at  0°.  or  32< 
IO.V.M-;  the  water  at  the  same  time  wiil  slowly  freeze.  Why  is  this?  It  is  manifestly 
owing  to  the  heat  fciven  out  in  the  solidification  of  the  water.  See  Fig  53. 

1 1.  Dissolve  sulphate  of  so  la  in  water  at  91°  F.  until  the  water  refuses  to  take  up  any 
more  of  the  salt ;  cork  the  bottle  containing  the  saturated  solution  tightly  and  set  it 


126  LIQUEFACTION. FREEZING    MIXTURES. 

aside  to  cool.  The  bottle  should  be  entirely  full  and  be  permitted  to  stand  very  quietly. 
If  it  be  agitated,  the  bottle  will  become  perceptibly  warm  to  tiie  hand  from  the  rsipid 
crystallization  and' solidification  of  its  liquid  contents.  If  shaking  the  l>ottie  be  not  suf- 
ficient to  produce  crystallization,  extract  the  tork  and  drop  in  a  bit  of  stick  or  a  small 
er^  stal. 

i  2.  Prepare  a  saturated  solution  of  acetate  of  soda,  and  when  cold  pour  it  over  the 
bulb  of  an  air  thermometer.  The  air  wLl  immediately  expand,  showing  the  evolution  of 
heat. 

1  J.  Freezing  Mixtures.  1.  To  sulphate  of  soda,  8  ounces,  add  5  ounces,  by 
weight,  of  chlorohydric  or  muriatic  acid.  Temperature  will  sink  from  50°  to  0°. 

2.  To  20  ounces  by  weight  of  a  mixture  of  equal  parts  of  sulphuric  acid  and  water, 
previously  mingled  and  cooled,  add  30  ounces  of  snow  or  pounded  ice ;  temperature  will 
gink  from  32°  to  — 23P. 

3.  To  sulphate  of  soda,  10  oz.,  add  8  fluid  oz.  of  a  mixture  of  equal  parts  of  sulphuric 
acid  and  water,  cooled  :  temperature  will  sink  from  50°  to  3°. 

4    Dissolve  powdered  sal  ammoniac  in  water  ami  note  the  diminution  of  temperature. 
5.  Dissolve  nitrate  of  ammonia  in  water ;  temperature  will  sink  from  50°  to  49° 
6    Dissolve  a  mixture  of  equal  parts  of  sal  ammoniac  and  nitre  in  water. 
7-  Common  salt,  1  part  by  weight ;  snow  or  pounded  ice,  2  parts ;  temperature  will 
sink  to  —5°. 

8.  Common  salt,  5  parts  by  weight ;  nitrate  of  ammonia,  5  parts  ;  snow  or  ice,  12  parts ; 
temperature  will  sink  to  — 25°. 

9.  <  hlorohvdric  acid,  5  parts  by  weight:  snow  or  ice,  8  parts:  temperature  will  sink 
from  32°  to  —27°. 

10  Chloro  hydric  acid,  5  parts,  poured  upon  8  parts  of  sulphate  of  soda,  will  reduce 
temperature  from  £0°  to  0°. 

11.  Crystallized  chloride  of  calcium,  and  2  parts  of  snow,  will  reduce  temperature  to 
— 40°,  and  freeze  mercury. 

12.  If  the  chloride,  in  the  last  experiment,  be  cooled  to  32°,  the  mixture  will  cause  a 
thermometer  to  fall  to  —50°, 


§  IV.— Effects  of  Heat:— Vaporization.— Ebullition. 

155.  Vaporization.  It  has  been  seen  that  the  first  effect  of 
heat  is,  to  separate  the  particles  of  bodies  from  each  other,  and  at 
the  same  time  to  elevate  their  temperature;  that  then,  as  the  heat 
accumulates,  the  force  of  cohesion  is  weakened  to  such  a  degree 
as  to  admit  of  the  easy  movement  of  the  particles  upon  each  other, 
and  the  solid  becomes  a  liquid ;  and  that  this  takes  place  without 
any  elevation  of  temperature.  If  the  heat  be  still  further  in- 
creased a  third  and  final  effect  is  produced.  In  the  ca^e  of  some 
substances  the  particles  are  pushed  so  far  from  each  other  as  to 
acquire  unlimited  freedom  of  motion,  and  the  substance  passes 
into  the  state  of  an  invisible  gas,  or  vapor,  resembling  the  at- 
mosphere. This  process  is  called  vaporization.  There  are 
some  substances,  such  as  ice,  arsenic,  sulphur,  camphor,  which 
can  yield  vapor  without  passing  through  the  intermediate  stale 
of  liquidity;  but  in  general  all  solid  bodies  are  first  liquefied,  and 
then  by  a  further  application  of  heat,  are  converted  into  vapors. 

155.  What  is  the  first  effect  of  heat  on  solids?  What  is  the  second?  If  the  bent  >e 
pushed  beyond  the  degree  required  for  liquefaction,  what  results?  What  is  vaporiza- 
tion.? Do  all  solids,  in  vaporizing,  pass  through  the  state  of  liquefaction? 


ABSORPTION    OF    HEAT  127 

156.  The  physical  properties  of  Vapors.    Vapors  are  trans- 
parent and  colorless,  like  the  gases ;  though  there  is  a  small 
number  of  colored  liquids  which  produce  colored  vapors.     In 
general,  they  possess  the  same  physical  properties  as  gases  ;  the 
chief  difference  between  them  is,  that  a  vapor  is  readily  con- 
densed into  a  liquid  by  a  diminution  of  temperature,  while  a 
gas  remains  in  the  aeriform  state  at  all  common  temperatures. 
The  effect  of  pressure  upon  vapor  is  the  same  as  upon  gases, 
provided  they  are  not  condensed  by  it,  i.  e.,  the  volume  which 
they  occupy  is  inversely  as  the  pressure.     Double  the  pressure 
and  the  volume  is  reduced  one  half.    The  expansion  of  vapors  by 
heat  is  also  the  same  as  that  of  gases,  i.  e.,  for  every  degree  of  heat 
added  to  them  they  expand  ^-^  of  the  bulk  which  they  occupy 
at  32°.     This  law  does  not  hold  good  unless  the  quantity  of  the 
vapor  heated  remains  the  same,  and  does  not  apply  to  cases 
where  fresh  portions  of  vapor  are  continually  rising  from  the 
liquid  by  which  they  are  produced ;  but  when  there  is  no  ad- 
dition made  to  the  quantity  of  the  vapor,  then  they  expand  just 
as  an  equal  volume  of  air  would  do,  and  thereby  exert  a  certain 
amount  of  mechanical  force.     It  is  always  to  be  borne  in  mind 
that  a  vapor,  unless  it  be  colored,  is  as  invisible  as  the  atmos- 
phere, and  that  its  particles  are  so  far  removed  from  each  other 
as  to  oppose  no  obstacle  to  the  passage  of  light. 

157.  Difference    between    Evaporation    and    Ebullition. 
Vapor  is  rising  at  all  times,  and  at  all  temperatures,  from  the 
S'irface  of  liquids,  but  the  higher  the  temperature,  in  general, 
the  more  rapid  the  process.    When  it  goes  on  quietly  and  slowly, 
at  natural  temperatures,  from  the  surface  of  liquids,  it  is  called 
evaporation ;  but  when,  by  the  application  of  a  large  amount 
of  heat,  vapor  is  formed  so  rapidly  at  the  bottom  of  a  vessel  as 
to  produce  violent  agitation  in  the  liquid,  it  is  called  boiling,  or 
ebullition.     The  subject  therefore  naturally  resolves  itself  into 
two  parts,  evaporation  and  ebullition ;  we  will  consider  the  lat- 
ter first. 

158.  Ebullition.    Ebullition,  or  the  rapid  and  violent  for- 
mation of  vapor,  takes  place  in  different  liquids  at  different 
temperatures ;  but  in  the  same  liquid,  under  the  same  circum- 
stances, always  at  the  same  temperature ;  and  this  is  called  its 
boiling  point.     Thus,  pure  water  boils  at  212°  F.,  alcohol  at 

156  State  the  physical  properties  of  vapors.  What  is  the  difference  between  a  vapor 
and  a  gas  ?  What  are  the  effects  of  pressure  on  vapors  and  gases  ?  Of  heat  ?  Are  va- 
pors always  invisible? — 157.  State  the  difference  between  evaporation  and  ebullition.— 
159.  Define  ebullition.  Is  the  boi'ing  point  of  the  same  liquid  always  constant?  State 
the  boiling  points  of  water,  Sulphuric  etaer.  Mercury,  &c. 


128 


IN    EBULLITION. 


Fig.  54. 


212 


m 


175°,  sulphuric  ether  at  96°,  sulphuric  acid  at  620°,  turpentine 
at  316°,  mercury  at  602°. 

159.  Absorption  and  disappearance  of  a  large  amount  of 
heat  during-  Ebullition.  The  most  important  fact  connected 
with  this  process  is,  that  it  is  attended  by  the  absorption  of  an 
enormous  amount  of  heat,  which  be- 
comes insensible  to  the  thermometer, 
just  as  in  the  case  of  liquefaction. 
The  fact  of  this  absorption  may  be 
proved  by  the  following  experiment: 
If 'we  half  fill  a  flask,  Fig.  54,  with 
pure  water  at  62°,  suspend  a  ther- 
mometer in  it,  and  place  it  over  a  lamp 
or  fire,  the  thermometer  will  steadily 
rise  until  the  water  reaches  the  tem- 
perature of  212°.  It  will  then  cease 
rising  and  continue  permanently  at  this 
point  until  the  water  is  all  boiled  away. 
Suppose  at  the  commencement  of  the 
experiment  that  the  water  was  at  62°, 
and  that  it  rose  to  212°,  the  boiling 
point,  in  six  minutes.  It  gained  then, 
in  these  six  minutes,  150°  of  heat,  or 
25°  each  minute.  This  is  the  rate  per 
minute  at  which  heat  entered  the  water.  The  time  occupied 
by  the  water  in  boiling  entirely  away  was  forty  minutes.  As 
it  was  receiving  heat  at  the  rate  of  25°  per  minute,  and  was 
forty  minutes  in  boiling  away,  it  is  quite  evident  that  in  the 
process  it  must  have  received  1000°  of  heat ;  yet  the  thermome- 
ter during  the  whole  time  did  not  rise  above  212°.  What  then 
has  become  of  this  1000°  of  heat?  It  has  evidently  entered 
into  the  steam  and  become  latent,  or  insensible  to  the  thermome- 
ter. It  has  been  ascertained  by  the  pyrometer,  (§  137,)  that 
red  heat  takes  place  at  980°.  Consequently,  an  amount  of  heat 
has  been  imparted  to  the  water  which,  if  it  had  been  a  solid 
substance,  like  iron,  would  have  heated  it  red-hot ;  and  yet  the 
water  has  indicated  only  the  temperature  of  212°!  This  sim- 
ple experiment  furnishes  satisfactory  proof  that  in  the  process 
of  vaporization  a  vast  amount  of  heat  is  absorbed  and  becomes 

159.  What  is  the  most  important  fact  connected  with  ebullition  ?  How  may  this  be 
proved  ?  How  much  heat  is  absorbed  or  made  latent  in  the  boiling  of  water  ?  How 
much  more  time  is  required  to  convert  a  given  weight  of  water  into  steam,  than  to 
heat  it  from  32°  to  212°  ? 


Heat  absorbed  in  Boiling, 


EVOLUTION    OF    HEAT 


129 


latent  and  insensible  to  the  thermometer,  that  it  requires  from 
5 ]r  to  6  times  as  much  time  to  convert  any  given  quantity 
of  water  into  steam,  as  it  does  to  raise  the  same  water  from  32° 
to  212°,  or  heat  it  180°,  and  consequently  that  5^  or  6  times  as 
much  heat  is  absorbed  in  the  conversion  of  water  into  steam  as 
is  necessary  to  raise  it  from  32°  to  212°  or  heat  it  by  180°,  i.  e.,, 
about  1000°. 

163  The  heat  absorbed  in  Vaporization  given  out  :  n  Con- 
densation. The  heat  thus  made  latent  in  the  conversion  of  a 
liquid  into  a  vapor,  is  again  given  out  and  made  sensible  when 
the  vapor  is  condensed  and  re-converted  into  a  liquid.  This 
may  be  proved  by  the  following  experiment,  Fig.  55.  Let  a 
be  a  strong  copper  vessel,  having  a  brass  tube  bent  twice  at 


Htut  git-en  out  in  Condensation  of  Steam. 

right  angles  connected  with  it,  and  dipping  beneath  the  surface 
of  water,  of  the  temperature  of  32°  in  the  glass  cup,/.  At 
d  there  is  a  thermometer  for  measuring  the  temperature  of  the 
water ;  c  is  a  stop-cock  opening  into  the  air ;  b  another  stop- 
cock commanding  the  entrance  to  the  tube.  A  powerful  lamp 
is  placed  beneath,  and  the  water  in  a  made  to  boil ;  c  is  then 
closed,  and  b  opened.  The  steam  rushes  into  the  cold  water  in 
ft  and  is  condensed  by  it,  until  this  also  has  reached  the  tem- 
perature of  212°.  The  water  in  f  will  then  begin  to  boil,  and 
the  steam  commence  rising  into  the  air.  The  amount  of  cold 


160.  Is  this  heat  annihilated?     Can  it  he  ohtaine<t  again  hy  condensation?     IIo-.v  is 
this  proved?     How  much  latent  heat  is  given  out  in  the  condensation  of  steam? 


130  IN    CONDENSATION. 

water,  at  32°,  contained  in  /at  the  beginning  of  the  experiment 
was  11  cubic  inches;  at  the  conclusion  of  the  experiment  the 
amount  of  water  has  been  increased  to  13  cubic  inches,  at  tem- 
perature of  212°.  It  has  increased  in  volume  by  two  cubic 
inches,  and  has  done  so  by  the  condensation  of  steam,  at  tem- 
perature of  212°,  from  the  copper  boiler.  The  latent  heat, 
therefore,  contained  in  two  cubic  inches  of  water  in  the  form  of 
steam,  of  the  temperature  of  212°,  has  raised  the  11  cubic 
inches  in  the  glass  cup  from  32°  to  212°.  The  amount  of  heat, 
therefore,  latent  in  two  cubic  inches  of  water  at  212°,  in  the 
form  of  steam,  is  sufficient  to  raise  the  temperature  of  a  volume 
of  water  in  the  liquid  state,  5J  times  greater  than  itself,  from 
32°  to  212°,  i.  e.,  by  180°.  Consequently,  the  sum  of  the  heat 
given  out  by  the  condensation  of  this  amount  of  steam  is  equal 
to  180X5^990°.  The  raising  the  temperature  by  180°,  of 
an  amount  of  water  5^  times  greater  than  the  amount  which 
has  been  condensed,  is  the  same  thing  as  raising  the  temperature 
of  an  amount  of  water  equal  to  that  which  has  been  condensed 
by  5 1  times  180°  — 990°;  from  which  we  see  -very  plainly  that 
the  amount  of  latent  heat  given  forth  in  the  condensation  of 
steam,  and  its  reconversion  into  a  liquid,  is  equal  to  the  amount 
of  latent  heat  absorbed  when  water  is  converted  into  vapor, 
i.  e.,  about  1000°  in  each  case.  These  important  facts  were 
first  demonstrated  by  Dr.  Black,  shortly  after  his  discovery  of 
the  heat  made  latent  in  the  process  of  liquefaction,  and  a  full 
account  of  it  may  be  found  in  the  1st  volume  of  Dr.  Black's 
Le  tures,  already  referred  to. 

151.  The  amount  of  heat  absorbed  is  not  the  same  for  all 
Vapors.  Equal  weights  of  different  liquids  require  very  differ- 
ent amounts  of  latent  heat  to  convert  them  into  vapor.  Thus, 
while  water  absorbs  and  renders  latent  1000°  of  heat,  ammonia 
absorbs  830°,  alcohol  386°,  ether  162°,  turpentine  133°.  The 
amount  of  heat  which  is  rendered  latent  in  each  case  may  be  de- 
termined by  distSll:ng  over  a  given  weight  of  the  liquid,  and  con- 
densing it  in  a  large  volume  of  wrater,  the  temperature  of  which  is 
noted  at  the  beginning  of  the  experiment,  and  also  at  its  close ; 
Fig.  56.  The  liquid  to  be  tried  is  placed  in  the  flask  A,  the 
neck  of  which  is  connected  with  a  glass  receiver,  B,  furnished 
with  a  spiral  condensing  tube  terminating  at  D  ;  this  receiver  is 
placed  in  a  vessel  c,  with  a  considerable  quantity  of  water,  the 
weight  of  which  has  been  accurately  determined.  The  liquid 

151.  Is  the  amount  of  heat  made  latent  the  same  for  all  vapors?     How  may  this 
amount  be  determined  for  each  ? 


BOILING    POINT    VARIABLE. 


131 


Fig.  56. 


| 


Determination  of  the  Latent  Htat  of  Vapors. 


in  A  is  distilled  over  into 
B  ;  the  quantity  that 
condenses  is  carefully 
weighed,  and  the  rise  of 
temperature  experienced 
by  the  water  used  for  con- 
densation is  estimated  by 
a  thermometer,  t.  The 
whole  is  enclosed  in  an 
outer  tin  plate  vessel,  and 
is  still  further  protected 
from  the  radiation  of  the 
lamp  by  the  tin  plate 
screen  R.  s  is  a  glass 
rod  for  agitating  the 


water.  A  pint  of  water 
converted  into  steam  will, 
on  condensation,  raise  the 
temperature  of  10  p'nls 
99°  and  a  fraction.  A 
gallon  of  water  converted 
into  steam,  at  212°,  and 
then  condensed,  will  raise  5  '  gallons  of  water  from  32°  to  212°, 
or  180°.  It  requires,  therefore,  5.}  times  as  much  water  at  32° 
to  condense  steam,  as  the  water  from  which  the  steam  was  origin- 
ally formed.  If  the  condensing  water  be  not  so  cold  as  32°,  a 
larger  quantity  of  it  will  be  needed.  By  careful  experiments 
of  this  kind  the  latent  heat  of  all  vapors  may  be  determined. 

162.  Boiling-  Point  variable— Influenced  by  the  pressure 
of  the  Atmosphere.  The  boiling  point  of  the  same  liquid  is  not 
to  be  considered  perfectly  constant;  it  depends  upon  circum- 
stances, the  most  important  of  which  is  the  pressure  of  the 
atmosphere  upon  its  surface.  This  pressure  is  equal  to  15  Ibs. 
(see  §  9,)  upon  every  square  inch  ;  it  operates  upon 
liquids,  as  well  as  solids,  and  its  effect  is  to  keep  the  par- 
ticles of  liquid  down,  and  prevent  them  from  passing  into  the 
vaporous  state ;  this  it  does  by  the  compression  which  it  exer- 
cises and  it  amounts  to  the  same  thing  as  adding  just  so  much 
to  the  cohesion  existing  in  the  liquid,  tending  to  keep  its  parti- 
cles together.  This  additional  cohesion  can  only  be  counterac'ed 
by  heat,  and  no  liquid  can  boil  until  it  has  acquired  heat  enough 

1^2    Ts  tho  boiling  point  ever  affected  hv  circnmstunces  ?     What  is  the  effect  of  a  varia- 
tion in  the  atmospheric  pressure?    Explain  this. 


132  MEASUREMENT   OF   HEIGHTS. 

to  overcome  this  pressure  of  the  atmosphere.  The  elasticity 
of  the  vapor,  or  its  tendency  to  expand,  must  be  equal  to  the 
force  which  tends  to  prevent  it  from  expanding ;  in  all  cases 
where  a  liquid  boils  in  the  open  air,  the  elasticity  of  the  vapor, 
and  the  pressure  of  the  atmosphere,  exactly  balance  each  other. 
Now  if  ;he  pressure  of  the  atmosphere  be  diminished,  the  elastic 
ibrce  required  to  balance  it  will  be  diminished  also ;  and  a?  this 
depends  upon  the  temperature,  the  heat  required  will  le  less. 
Consequently,  if  the  atmospheric  pressure  be  diminished,  boiling 
will  take  place  at  a  lower  temperature ;  if,  on  the  other  hand, 
the  atmospheric  pressure  be  increased,  more  elastic  force  must 
be  possessed  by  the  vapor  before  it  can  rise,  and  this  it  can  not 
have  without  additional  heat ;  boiling,  therefore,  must  take  place 
at  a  higher  temperature.  This  can  readily  be  shown  by  experi- 
^ment.  Remove  the  pressure  from  warm 
Fig.  57.  water  by  means  of  the  air  pump,  and  it  will 

boil  at  the  temperature  of  70°,  Fig.  57. 
Sulphuric  ether,  in  a  vacuum,  will  boil  at 
— 46°,  or  140°  lowrer  than  in  the  open  air, 
at  a  temperature  such  that  water  will  easily 
freeze  in  contact  with  it,  as  may  be  proved 
by  experiment.  As  we  ascend  in  the  at- 
mosphere the  pressure  of  the  air  diminishes, 
consequently  the  boiling  point  is  lowered. 
So  regularly  does  this  decline  take  place 
_  that  it  affords  a  measure  of  height.  A  fall 

water  Boiling  at  IQO.  of  1°  F.  indicates  an  elevation  of  596  feet. 
On  the  contrary,  at  the  bottom  of  mines  the 
boiling  point  is  raised  in  consequence  of  the  increase  of  the  at- 
mospheric pressure.  At  the  Hospital  of  St.  Bernard,  on  the 
Alps,  about  8,400  feet  above  the  sea,  water  boils  at  196°;  on 
the  top  of  Mount  Blanc,  at  184°.  In  consequence  of  this  low 
temperature,  it  has  been  found  difficult  to  cook  food  by  boiling 
at  these  high  points,  as  the  solvent  power  of  water,  and  its  effi- 
cacy in  cooking  meats  and  vegetables,  depends  upon  its  tempera- 
ture. This  difficulty  has  been  obviated  by  the  use  of  Papin's 
Digester,  an  instrument  to  be  described  hereafter.  It  is  evident, 
from  this,  that  it  is  necessary  to  take  the  height  of  the  barome- 
ter into  the  account  in  a!l  experiments  upon  the  boiling  points 

What  is  the  effect  of  removing  the  atmospheric  pressure  altogether?  What  is  the 
effect  of  elevation  in  the  air  upon  the  boiling  point?  What  practical  difficulty  results 
from  this?  What  is  the  variation  of  the  boiling  point  within  the  ordinary  range  of  the 
barometer  ? 


CIRCUMSTANCES    AFFECTING  133 

of  liquids.  A  variation  of  one-tenth  of  an  inch  makes  a  differ- 
ence of  more  than  ^°  F.,  so  that,  within  the  ordinary  range 
of  the  barometer,  the  boiling  point  of  water  may  vary  5°. 

163.  Wollaston's  Hypsometer.    It  has  been  stated  that  the 
lowering  of  the  boiling  point,  in  proportion  to  the  elevation 
above  the  level  of  the  sea,  is  made  use  of  as  a  means  of  meas- 
uring the  height  of  mountains.     It  is  only  necessary  to  note 
the  temperature  of  water  boiling  at  the  ba^e  of  the  mountain, 
and  then  at  the  point  of  elevation.     (1°  F.  is  equivalent  to  596 
feet  in  height.)     An  instrument  for  taking  these  observations 
successfully,  was  invented  by  Archdeacon  Wollaston,  arranged 
in  such  a  way  that  a  1000th  part  of  a  degree  of  the  thermome- 
ter might  be  read  upon  the  scale,  and  so  delicate  was  it  that  the 
effect  produced  upon  the  boiling  point  by  the  height  of  an  ordi- 
nary table  could  readily  be  ascertained. 

164.  Influence  of  adhesion  on  the  boiling-  point    Adhesion 
of  the  liquid  to  the  surface  of  the  vessel  has  a  decided  effect 
upon  the  boiling  point;  and  as  the  degree  of  adhesion  depends 
upon  the  substance  employed,  the  material  of  which  the  ve-sel 
i^  made  ha?  some  effect  upon  the  boiling  point.     Thus  water 
sometimes  boils  at  214°  in  a  glass  vessel,  but  falls  to  212°  if  a 
few  iron  filings  be  dropped  in ;  this  was  fir  -t  noticed  by  Gay 
Lu-^sac.     If  the  inside  of  a  vessel  be  varnished,  the  boiling  will 
sometimes  not  take  place  short  of  221°,  and  then  will  proceed 
irregularly,  the  temperature  falling  to  212°,  at  every  occurrence 
of  boiling.     The  presence  of  a  little  oil  upon  the  surface  of  a 
liquid  also  elcva'.e.s  the  boiiing  point.     Af.er  sulphuric'  ac'd  has 
been  boiled  in  a  glass  flask,  the  boi  ing  point  is  said  to  be  ele- 
vated five  or  six  degrees.     In  all  these  cases  the  effect  is  due 
to  the  attraction  of  adhesion  exerted  by  the  surface  in  question 
upon  the  water,  which  tends  to  retain  it  in  the  liquid  stale,  anJ 
this  can  only  be  overcome  by  an  addition  to  the  temperature. 
It  takes  place  with  other  liquids.,  as  well  as  water,  and  with  sonu 
of  them  to  a  much  greater  extent.     Though  the  temperature 
of  the  boiling  water  may  be  thus  elevated,  the  temperature  of 
the  vapor  formed  is  always  at  212°,  or  at  whatever  point  the 
atrno  ;pheric  pressure  at  the  time  may  require.     As  a  general 
rule,  however,  the  temperature  of  the  liquid  boiling,  and  the 
vapor  formed,  are  exactly  the  same. 

165.  The  Air  dissolved  in  Water  favors  its  Ebullition. 


1G3.  Describe  Wollaston'a  Hypsometer. — 1(14.  What  is  the  effect  of  adhesion  on  the 
boiling  point?  Give  some  illustrations. — 105  What  effoct  has  the  air  dissolved  iu 
water  upon  its  boiling  ?  If  air  be  entirely  expelled  from  water,  wliat  results  ? 


134  THE    BOILING    POINT. 

Water  possesses  the  power  of  dissolving  air.  This  may  be 
proved  by  heating  water  in  a  flask,  over  a  spirit  lamp,  when  the 
air  may  be  seen  to  separate  from  the  water  in  the  form  of 
bubbles,  and  rise  to  the  surface.  These  bubbles  of  air 
furnish,  as  it  were,  an  avenue  of  escape  to  the  steam ;  and  at 
the  same  time,  the  presence  of  so  large  an  amount  of  aeriform 
matter  tends  to  diminish  the  cohesion  of  the  particles  of  water, 
and  to  facilitate  the  separation  that  is  necessary  to  enable  them 
to  assume  the  state  of  vapor.  If  the  air  be  expelled  from  water 
by  long  continued  boiling,  it  may  be  heated  in  an  open  glass 
vessel  to  the  temperature  of  360°,  without  boiling.  The  heat 
thus  collected  in  the  water  causes  it  to  flash  into  steam  almost 
instantaneously,  with  a  loud  report,  when  it  does  boil,  and  the  ves- 
sel is  generally  broken;  the  temperature  of  the  vapor  formed  is 
only  212°,  and  that  of  the  water  immediately  sinks  to  the  same 
point.  It  is  extremely  difficult  to  expel  all  the  air  from  water 
boiling  in  vacuo  for  some  time  will  not  effect  it.  If  water,  how- 
ever, be  slowly  frozen,  the  air  is  entirely  expelled,  and  if  a  lump 
of  this  ice  be  immersed  in  heated  oil,  or  turpentine,  F o  as  to  melt 
without  coming  into  contact  with  the  air,  it  may  be  heated  to 
many  degrees  above  212°  without  boiling,  and  will  then  suddenly 
be  converted  into  vapor  with  great  violence.  Liquids  which  con- 
tain but  little  air,  and  which  require  but  little  latent  heat  to 
pass  into  vapor,  such  as  alcohol,  ether,  and  sulphuric  acrd,  boil 
with  great  irregularity,  and  with  sudden  bursts,  instead  of  with 
the  regularity  and  steadiness  of  water. 

166.  Solids  dissolved  in  a  Liquid  elevate  its  Boiling  Point. 
The  boiling  point  of  a  liquid  is  not  changed  by  the  presence  of 
foreign  bodies,  which  are  mechanically  diffused  through  it  like 
sand  or  mud  in  water ;  but  it  is  changed  by  all  substances  which 
are  capable  of  forming  a  true  so'ution  with  it.     Thus  rosins 
dissolved  in  alcohol,  retard  its  boiling ;  salts  dissolved  in  water, 
elevate  the  boiling  point ;  acids   the  same ;  alcohol  seems  to 
lower  it.     This  is  owing  to  the  attraction  of  adhesion,  exerted 
by  the  substances  in  question,  which  tends  to  bind  the  particles 
of  water  closely  to  itself,  and  to  prevent  them  from  escaping. 
A  saturated  solution  of  common  salt  boils  at  227°  ;  of  nitre,  at 
240°  ;  sal  ammoniac,  at  238°  ;  chloride  of  calcium,  355°. 

167.  Increase  of  Pressure  elevates  the  Boiling-  Point;— 
Diminished  Pressure  lowers  it.    If  water  be  boiled  in  a  close 

What  is  the  effect  of  in  trod  vu-  in  £  ice  into  heated  oil  of  turpentine  ? — K6.  What  effect 
has  the  solution  of  solids  in  a  liquid  upon  the  boiling  point?— 167.  What  is  the  effect 
of  increased  pressure  on  the  boiling  point .' 


ELEVATION    OF    BOILING    POINT 


1 


vessel,  the  steam  collecting  in  the  upper  part  soon  presses  on 
the  surface  of  the  water  with  so  much  force  as  to  put  an  entire 
stop  to  the  whole  process  of  ebullition,  and  it  will  not  recom- 
mence until  the  water  has  been  heated  considerably  above  212°. 
This  may  be  shown  by  boiling  water  in  a  strong  glass  flask,  pro- 
vided with  a  stop-cock,  and  having  a  thermometer  immer.-ed  in 
the  fluid.  The  stop-cock  being  open,  the  water  will  boil  at 
212° ;  but  if  the  stop-cock  be  closed,  in  a  few  minutes  the  boil- 
ing will  be  seen  to  cease,  so  that  there  will  be  no  agitation  of 
the  surface,  and  it  will  not  recommence  until  the  thermometer 
has  risen  several  degrees.  If,  then,  at  this  moment,  the  stop- 
cock be  opened,  the  steam  will  rush  out,  pressure  will  be 


Fig.  58. 


removed,  boiling  will  recommence  with 
great  violence,  and  the  thermometer  im- 
mediately sink  to  212° ;  Fig.  58.  It  is 
quite  evident  from  this  experiment  that 
increase  of  pressure  elevates  the  boiling 
point.  If  the  spring  safety  valve  screwed 
upon  the  stop-cock  be  removed,  and  air 
be  forced  into  the  flask,  the  stop-cock 
then  closed,  and  the  fla-k  placed  over  a 
spirit  lamp,  a  longer  time  will  be  required 
than  before  for  the  water  to  boil,  and  it 
will  not  do  so  until  the  thermometer  has 
risen  considerably  above  212°,  depending 
upon  the  amount  of  air  forced  in;  this 
also  proves  the  effect  of  increased  pres- 
sure in  elevating  the  boiling  point.  On 
the  contrary,  if  a  flexible  tube  be  attached 
to  this  flask,  and  the  air  be  exhausted  by 
the  air  pump,  the  water  will  boil  at  a 
temperature  lower  than  212°,  because 
the  natural  pressure  of  the  atmosphere 
is  removed  from  it. 

168.  Elcvrr  cm  of  ths  boiling-  pomt 
indicates  Increase  of  Pressure.  This 
principle  is  very  snti-factorily  illustrated 
in  the  apparatus  of  Dr,  Marcet,  repre- 
sented in  Fiq.  59.  B  is  a  strong  iron  g'obe,  about  half  filled 
with  water,  and  having  mercury  at  the  bottom  to  the  depth  of 


Steam  Flask. 


Describe  the  stenm  flask.  -168.  How  may  increase  of  pressure  be  inferred  frrom  the 
elevation  of  the  boiling  point  i 


136 


SHOWS    INCREASED    PRESSURE. 


Fig.  59. 


30  in 


about  an  inch ;  t  is  a  thermometer  screwed  steam  tight  into  the 
globe  and  graduated  as  high  as  500°.  It  indicates  the  tempera- 
ture of  the  steam  in  the  upper  part  of  the  globe ;  c  is  a  stop- 
coc-k,  which  can  be  opened  or  shut  at  pleasure ;  a  is  a  long  and 
strong  tube,  graduated  into  inches  and  parts  of  an  inch,  open 
at  both  ends,  and  the  lower  extremity  dipping  beneath  the  level 
of  the  mercury.  The  water  is  made  to  boil  vigorously  by  the 
flame  of  the  lamp,  and  the  stop-cock  being  open  and  steam 
escaping,  the  thermometer  will  indicate  the  temperature  of 
212°,  and  the  mercury  remain  stationary  at  the  foot  of  the  tube. 
The  pressure  of  the  steam  at  this  moment,  -in  the  interior  of  the 
apparatus  is  sufficient  to  drive  out  all  the  air,  and  amounts  to  1  f)  Ibs. 
upon  every  square  inch.  If  the  stop- 
cock be  now  closed,  the  steam,  having 
no  avenue  of  escape,  begins  to  collect 
in  the  top  of  the  globe,  and  to  react  upon 
the  water.  The  pressure  thus  created 
puts  a  stop  to  the  boiling  of  the  water. 
The  heat  proceeding  from  the  lamp  is 
no  longer  wanted  in  order  to  become 
latent  in  the  vapor,  there  being  no  vapor 
formed ;  the  temperature  of  the  whole 
apparatus  rises,  and  the  thermometer 
every  moment  indicates  a  temperature 
steadily  increasing  above  2 1 2°.  At  the 
same  time  the  increased  pressure  causes 
the  mercury  to  rise  in  the  tube,  «,  and 
it  at  length  makes  its  appearance  above 
the  globe,  so  as  to  be  plainly  seen.  As 
the  temperature  rises  higher  and  higher, 
the  mercury  in  a  advances  steadily  up- 
wards, indicating  the  gradual  increase  of 
the  pressure  in  the  interior  of  the  boiler. 
When  the  mercury  has  reached  the 
height  of  30  inches,  it  is  an  indication 
that  the  pressure  in  the  interior  of  the 
boiler  is  now  two  atmospheres,  or  twi  e 
15  Ibs.  to  the  square  inch,  i.  e.,  3J 
Ibs.  ;  and  if  the  thermometer  be 
noted  at  this  moment  it  will  be  found  to 
Manet's  Apparatus.  stand  at  250°.  "When  the  thermometer 


Describe  Marcet's  apparatus.     What  reduction  must  be  made  upon  the  actual  press- 

'irc  iu  order  to  calculate  ilic  explosive  force .' 


THE  CULINARY    PARADOX. 


137 


has  reached  275°  the  mercury  will  have  risen  60  inches  in  the 
tube,  and  the  pressure  will  be  45  Ibs.  to  the  square  inch;  when 
it  has  attained  294°,  the  mercury  in  the  tube  will  have  ascended  90 
inche  •,  and  the  pressure  will  have  increased  to  four  atmo  pheres, 
or  GJ  Ibs.  to  the  square  imh.  As  temperature  rises,  pressure 
steadily  increases,  because  with  every  addition  of  heat  the 
greater  the  tendency  of  the  water  to  flash  into  steam,  and  eventu- 
ally the  globe  will  be  burst  by  the  process.  If  now,  under 
these  circumstances,  the  stop-cock  be  suddenly  opened,  the 
pressure  will  be  removed  from  the  surface  of  the  water,  a  large 
quantity  will  flash  into  steam,  absorbing  an  immense  amount 
of  heat,  and  the  mercury  in  the  thermometer  w  11  immediately 
sink  to  212°.  It  is  evident,  therefore,  that  the  temperature  of 
the  steam  in  a  boiler  is  a  sure  exponent  of  the  amount  of  the 
pres  u;-e  in  the  interior. 

The  pressures  just  given  are  the  actual  pressures  produced  by 
the  elastic  force  of  the  vapor,  but  as  ihe  atmosphere  presses  upon 
the  outside  of  the  globe  with  a  Ibrce  of  15  Ibs.  to  the  square  inch, 
the  pressure  tending  to  burst  the  globe  is  found  by  ded  ;c  ing 
this  amount  from  the  actual  pressure,  and  consequently  250°  of 
the  thermometer  is  said  to  indicate  a  pressure  of  15  Ibs.,  2753  a 
pressure  of  30  Ibs.,  294°  a  pressure  of  45  Ibs.  to  the  square  inch. 
The  sudden  falling  of  the  thermometer  to  212°  on  opening  the 
stop-cock  is  explained  by  the  immense  absorption  of  heat  conse- 
quent upon  the  rapid  passage  of  so  much  water  from  the  liquid  to 
tiie  aeriform  state.  That  it  is  not  owing  to  the  escape  of  the  steam, 
but  to  its  formation,  might  be  shown  by  discharging  the  steam 
into -a  c'oied  vessel,  heated  to  2 12°,  from  whi  h 
none  of  it  cou'd  escape.  At  the  close  of  the 
experiment  the  steam  in  the  closed  vessel 
would  be  found  to  be  only  at  the  temperature 
of  212°.  The  water  in  the  boiler  has  then 
lost  heat,  but  nothing  else  has  been  apparently 
heated  by  it.  The  diminution  of  temp  -rature 
is  due,  therefore,  to  the  sudden  passage  of  a 
q:mn  ity  of  water  into  the  state  of  vapor,  by 
which  a  large  amount  of  heat  has  been  made 
latent  and  become  insensible  to  the  ther- 
mometer. 

1C9.     The    Culinary    Paradox.     Water 
Culinary  p.tra  /cz.       made  to  boil  by  the  application  of  Cold.    AVe 


Fig.  60. 


169.  Describe  the  culinary  paradox,  and  explain  it. 


103 


EXPANSION    OF    WATER    IN    FORMING    STEAM. 


have  seen  that  boiling  has  been  made  to  cease  in  the  steam 
flask,  Fig.  58,  by  closing  the  stop-cock.  It  can  be  made  to  re- 
commence by  the  application  of  cold  water.  The  effect  of  the 
cold  water  is  to  condense  the  steam  in  the  upper  part  of  the 
flask;  consequently  there  is  a  vacuum  formed;  pressure  is 
removed  from  the  surface  of  the  water,  and  it  will  recommence 
boiling  with  great  violence.  If,  at  the  moment  when  the  water 
first  begins  to  boil  again,  the  stop-coc'k  be  opened,  the  air  will 
rush  in  with  a  hissing  noi  e,  showing  conclusively  the  existence 
of  the  vacuum.  This  experiment  may  be  performed  with  an 
ord;nary  glass  flask.  Boil  a  little  water,  and  when  the  steam  is 
escaping,  cork  it  tightly ;  take  it  from  the  lamp  and  pour  cold 
water  over  the  upper  part ;  the  boiling  will  recommence  and 
proceed  with  vigor ;  apply  hot  water,  and  it  will  again  cease. 
Remove  the  cork  beneath  the  water  and  the  inverted  flask  will 
be  at  once  filled,  showing  the  formation  of  a  vacuum  by  the 
condensation  of  the  steam.  Fig.  60. 

170.  Expansion  of  Liquids  in  passing-  into  Vapor,— espe- 
cially water,  in  forming-. Steam.  Vapors  occupy  more  space 
than  the  liquids  from  which  they  are  pro- 
duced. Water,  at  its  point  of  greatest  densi- 
ty, viz.,  39.5°,  expands  in  passing  into  vapor, 
1696  times,  or  in  round  numbers,  1700  times ; 
i.  e.,  a  cubic  inch  of  water  makes  about  a 
cubic  foot  of  steam.  Alcohol  expands  493 
times  ;  ether,  212  times.  The  amount  of  this 
expansion  in  the  case  of  water  may  be  readily 
shown  by  the  apparatus  represented  in  Fig. 
61.  The  cylinder,  ft,  is  fitted  with  a  steam- 
tight  piston,  a  p.  The  weight  of  the  piston 
is  accurately  balanced  by  means  of  the  weight, 
w,  so  that  it  will  remain  stationary  in  any 
position  in  the  cylinder  in  which  it  may  be 
placed,  without  tending  to  move  up  or  down, 
and  exerting  no  pressure  upon  anything 
placed  below  it.  Now  let  a  very  small 
quantity  of  water  be  introduced  into  the 
cylinder  below  the  piston,  and  the  heat  of 
a  lamp  applied.  The  temperature  of  the 
Expansion  of  Water,  water  will  steadily  rise  to  212°,  after  whicii 

170.  What  js  the  expansion  which  different  liquids  iindergo  in  vaporizing?  How  may 
ff.is  he  proved  in  the  case  of  water?  If  water  be  toiled  below  212°  what  effect  has 
tuis  on  expausiou? 


THE    CONDENSATION    OF    STEAM.  139 

it  will  remain  stationary,  and  an  invisible  vapor  or  gas  will  be 
formed,  and  the  piston  gradually  rise.  This  process  will  go  on 
until  the  whole  of  the  water  has  been  converted  into  steam. 
On  measuring  the  space  occupied  by  the  steam  and  compar'ng 
it  with  the  space  occupied  by  the  water  at  the  commencement 
of  the  experiment,  it  will  be  found  to  be  1G96  times  greater; 
in  other  words,  the  water,  in  passing  into  vapor,  has  expanded 
1696,  or  nearly  1700  times;  and  as  a  cubic  foot  contains  1728 
cubic  inches,  we  may  say  in  round  numbers,  that  a  cubic  inch 
of  water  will  make  a  cubic  foot  of  steam.  This  expansion 
takes  place  against  the  pressure  of  the  atmosphere,  (the  piston 
lifting  the  atmospheric  column  as  it  rise-)  which  amounts  to 
15  Ibs.  on  every  square  inch.  If  this  pressure  were  diminished 
the  water  would  expand  more  than  1700  times  in  passing  i..to 
steam ;  if  it  were  increased,  it  would  expand  less.  In  genera1, 
however,  as  the  average  pressure  of  the  atmosphere  is  about 
15  Ibs.  to  the  square  inch,  we  conclude  that  water,  parsing  into 
the  state  of  steam,  in  the  open  air,  expands  1700  times.  If 
water  be  boiled  at  a  temperature  lower  than  212"  the  expans'on 
which  it  undergoes  in  passing  into  vapor  will  be  proportionably 
increased;  thus,  if  it  be  made  to  bo:l  at  77°,  one  cubic  inch  will 
expand  into  23,090  cubic  inches  of  vapor ;  if  it  boil  at  68°,  it  will 
expand  into  58,224  cubic  inches.  This  expansion  of  water,  in 
passing  in'o  steam,  is  one  of  the  moving  forces  in  the  steam 
eng  ne,  and  the  efficient  working  of  this  extraordinary  machine 
depends  upon  this  simple  fact. 

171.  Condensation  of  Steam  or  its  reconversion  into 
Water,  by  decrease  of  temperature.  One  of  the  mo  t  remark- 
able properties  of  steam  is  its  ready  condensation  into  water, 
occupying  1700  times  less  space  than  itself  as  soon  as  its  tem- 
perature is  reduced  below  21*2°.  Thus,  if  in'o  the  cylinder,  repre- 
sented in  Fig.  61,  in  which  the  piston  has  been  driven  up  by 
the  conversion  of  the  water  into  steam,  a  little  coM  water  at 
32°  be  introduced  beneath  the  piston,  the  steam  will  be  instantly 
condensed  into  water,  occupying  1700  times  less  space  than  the 
vapor ;  a  vacuum  will  consequently  be  famed  beneath  the  pis- 
ton, and  as  the  cylinder  is  open  to  the  air  at  the  top,  the  press- 
ure of  the  atmosphere  will  drive  the  piston  down  with  a  force 
of  15  Ibs.  to  every  square  inch.  If  the  pisloii  pos.-ess  an 
area  of  one  square  foot  the  atmospheric  pressure  will  be  ob- 

171  How  may  steam  readily  be  reconverted  into  water  ?  What  effect  is  produced  upon 
the  steam  in  a  steam  cylinder  by  injecting  cold  water?  What  force  is  brought  into  play 
by  this  condensation  ? 


140 


THE    STEAM    ENGINE. 


tamed  bj  multiplying  144,  the  number  of  square  inches  in  this 
area,  by  15  =z  2 1 60  Ibs. ;  in  other  words,  the  atmospheric  pressure, 
in  this  case,  will  be  almost  one  ton.  The  completeness  of  the 
vacuum,  and  the  degree  of  atmospheric  pressure,  will  depend 
upon  the  temperature  of  the  condensing  water ;  if  it  be  not  so 
co'.d  as  32°  the  vapor  will  not  be  entirely  condensed,  the  vacuum 
not  FO  perfect,  and  the  atmospheric  pressure  proportionably  di- 
m'nished.  Hence  we  have  a  second  force,  brought  into  play  by 
the  vacuum  created  by  condensed  steam.  Both  these  forces, 
the  expansion  of  water  in  vaporization,  and  the  atmospheric 
pressure,  are  employed  in  the  condensing  steam  engine. 

FiS-  G2-  172.    Wollaston's  Steam  Bulb.    Both 

these  forces  arc  admirably  illustrated  by 
a  little  instrument  represented  in  Fig. 
62.  It  consists  of  a  metallic  bulb,  sur- 
mounted by  a  cylinder  of  the  same,  into 
which  a  steam-tight  piston  is  fitted.  The 
bulb  should  be  half  filled  with  water  and 
held  over  a  lamp.  When  the  water 
boils  it  expands,  in  passing  into  steam, 
1700  times,  and  drives  the  piston  up. 
Now  remove  the  lamp  and  dip  the  bulb 
into  cold  water;  immediately  the  steam 
is  condensed,  a  vacuum  is  formed,  the 
pressure  of  the  atmosphere  is  brought 
into  action,  and  the  piston  is  driven  down 
with  very  considerable  force.  In  the 
steam  engine  this  double  process  is  re- 
peated alternately  on  each  side  of  the 
piston  for  every  stroke.  The  great  im- 
provement of  Mr.  Watt,  in  the  steam  en- 
grne,  consisted  in  condensing  the  steam 
in  a  condenser,  separated  from  the  cylin- 
der, FO  as  to  avoid  the  necessity  of  cooling  the  cylinder  below 
212°,  or  the  boiling  point  of  water,  for  every  stroke  of  the  pis- 
ton. 

173.  The  Steam  Engine.  This  wonderful  machine  was  per- 
fected by  Mr.  James  Watt,  of  Glasgow,  in  Scotland,  about  the 
year  1765.  His  great  improvement  consisted  in  the  condensa- 
tion of  the  steam  in  a  vessel  appropriated  exclusively  to  this 
purpose,  called  the  condenser.  He  was  thus  led -to  notice  the 


Wottaston's  Steam  Bulb. 


172.  Describe  Wollaston's  steam  bulb.    What  two  forces  does  it  illustrate  ?— 173.  Who 
invented  the  steam  engine  ? 


MR.  WATT'S  IMPROVEMENTS.  141 

immense  absorption  of  heat  which  takes  place  when  water  is 
converted  into  steam,  and  its  evolution  again  when  the  steam  is 
condensed  inro  water, — a  subject  which  had  been  previously 
investigated  by  Dr.  Black,  who  was  at  that  time  Prof,  of  Medi- 
cine and  Lecturer  on  Chemistry  in  the  University  of  Glasgow, 
and  an  intimate  friend  of  Mr.  Watt.  The  following  is  the  ac- 
count given  by  Dr.  Black  of  the  successive  steps  in  the  im- 
provement of  the  steam  engine:  "About  that  time  Mr.  Watt 
came  to  settle  in  Glasgow,  as  a  maker  of  mathematical  instru- 
ments ;  but  being  molested  by  some  of  the  corporations,  who 
considered  him  as  ah  intruder  on  their  privileges,  the  University 
protected  him  by  giving  him  a  shop  within  their  precincts,  and 
by  conferring  on  him  the  title  of  'Mathematical  Instrument 
Maker  to  the  University.'  I  soon  had  occasion  to  employ  him 
to  make  some  things  which  I  needed  for  my  experiments,  a..d 
found  him  to  be  a  young  man  possessing  most  uncommon  tal- 
ents for  mechanical  knowledge  and  practice,  with  an  originality, 
readiness,  and  copiousness  of  invention,  which  often  surprised 
and  delighted  me  in  our  frequent  conversations  together.  A 
few  years  after  he  was  settled  at  Glasgow,  he  was  employed 
by  the  Professors  of  Natural  Philosophy  to  examine  and  rectify 
a  small  model  of  a  steam  engine  which  was  out  of  order.  This 
turned  a  part  of  his  thoughts  and  fertile  invention  to  the  nature 
and  improvement  of  steam  engines,  to  the  perfection  of  their 
machinery,  and  to  the  different  means  by  which  their  great  con- 
sumption of  fuel  might  be  diminished.  He  soon  acquired  such 
a  knowledge  on  this  subject  that  he  Avas  employed  to  plan  and 
erect  several  engines,  in  different  places,  while  at  the  same  time 
he  was  frequently  making  new  experiments  to  lessen  the  waste 
of  heat  from  the  external  surface  of  the  boiler,  and  from  that 
of  the  cylinder.  But  after  he  had  been  thus  employed  a  con- 
siderable time  he  perceived  that  by  far  the  greatest  waste  of 
heat  proceeded  from  the  waste  of  steam  in  filling  the  cylinder. 
In  filling  the  cylinder  with  steam,  for  every  stroke  of  the  com- 
mon engine  a  great  part  of  the  steam  is  chilled  and  condensed 
by  the  coldness  of  the  cylinder  before  this  last  is  heated  enough 
to  qualify  it  for  being  filled  with  elastic  vapor,  or  perfect  steam  ; 
he  perceived,  therefore,  that  by  preventing  this  waste  of  steam, 
an  incomparably  greater  saving  of  heat  and  fuel  would  be  at- 
tained than  by  any  other  contrivance.  It  was  thus  that,  in  the 
beginning  of  the  year  1765,  the  fortunate  thought  occurred  to 

Give  the  history  of  its  improvement. 


142  TWO    FORMS    OF    STEAM    ENGINE. 

him  of  conden-ing  the  steam  by  cold,  in  a  separate  vessel,  or 
apparatus,  between  which  and  the  cylinder  a  communication 
was  to  be  opened  for  that  purpose  every  time  the  steam  was  to 
be  condensed,  while  the  cylinder  itself  might  be  preserved  per- 
petually hot,  no  cold  water  or  air  being  ever  admitted  into  its 
cavity."  Such  is  Dr.  Black's  account  of  the  invention  of  the 
steam  engine.  It  was  soon  brought,  by  Mr.  Watt,  to  the  high- 
est degree  'of  perfection,  so  as  to  leave  hardly  anything  to  be 
d'sired,  either  in  regard  to  its  principles,  or  mechanical  detaiK 
•The  model,  alluded  to  by  Dr.  Black  is  still  preserved  in  the 
Cabins!  of  kite  University  of  Glasgow. 


Two  forms  of  the  Steam  Engine.  There  are  two 
'.forms  of  it,  differing  essentially  from  each  other,  viz.,  the  con- 
den  ing  and  non-condensing  engine.  In  the  former,  loih  the 
two  forces  described  above,  viz.,  the  expansive  force  of  steam, 
and  the  pressure  of  the  atmosphere  brought  into  play  by  its 
condensation,  are  employed;  hence  this  is  called  the  con- 
densing engine,  or,  the  low-pressure  engine.  In  the  latter,  only 
one  of  the  two  forces  described,  viz.,  the  expansive  force  of 
steam,  is  employed;  and  as.  only  this  one  force  is  used,  it  is 
necessary,  in  order  to  obtain  an  equal  effect,  to  make  use  of 
steam  possessing  an  expansive  power  of  at  least  15  Ibs.  to 
the  square  inch  greater  than  in  the  condensing  engine  ;  conse- 
quently this  is  called  the  non-condensing,  or  high-pressure  en- 
gine. 

175.  Condensing-  and  Non-condensing-  Engines.  The  dif- 
ference between  the  two  forms  of  the  steam  engine  is  indicated 
in  Fig.  63.  In  1,  the  piston  having  been  driven  dowrn  by  the 
steam,  is  rising  again  by  the  pre-sure  of  a  fresh  supply  from  the 
boiler  through  the  pipe,  BO  The  steam  that  drove  it  down  is 
issuing  through  the  stop-cock  at  the  top,  which  is  open  for  its 
escape,  into  the  air,  and  it  is  very  evident  that  the  piston  in  ris- 
ing is  acting  against  the  pressure  of  the  atmosphere,  and  has  to 
lift  a  column  of  air  of  the  same  area  with  itself,  extending  to 
the  upper  limit  of  the  atmosphere,  and  pressing  with  a  weight  of 
15  Ibs.  upon  every  square  inch;  all  of  which  the  steam  be'ow 
the  piston  is  obliged  to  raise,,  In  order  to  raise  this  immense 
weight,  amounting  to  nearly  2200  Ibs.  to  the  square  foot,  the 
steam  must  be  of  high  pressure  ;  and  as  it  is  also  let  off  into  the 
air  and  escapes  after  having  done  its  work  in  driving  the  piston, 

174.  What  are  the  two  forms  of  the  stenm  engine  ?  State  the  difference  between  them. 
—175.  Describe  Fig.  63,  showing  the  difference  between  the  condensing  and  non-con- 
densing engine. 


THE    MOST    COMPLETE    FORM 


143 


without  being  condensed,  this  form  of  the  steam  engine  has  re- 
ceived the  name  of  the  High-pressure  and  Non-conden.-ing  en- 
gine. In  2,  the  piston  having  been  driven  down  by  the  force  of 
the  steam,  is  ascending  by  the  pressure  of  a  fresh  supply  from 


Principle  of  Non-condensing  and  Condensing  Steam  Engines. 

the  boiler  through  the  tube  B.  The  steam  that  drove  it  down, 
however,  instead  of  escaping  through  the  stop-cock  c,  which  is 
closed,  passe 5  through  the  stop-cock  o,  into  an  adjo'ning  vessel, 
c,  called  the  condenser,  where  it  comes  into  contact  with  a 
stream  of  cold  water,  by  which  it  is  immediately  condened  into 
a  quantity  of  water  170!)  times  le>s  than  itself,  and  a  vacuum 
at  once  created.  As  soon  as  this  takes  place,  the  steam  still 
remaining  in  the  cylinder,  rushes  through  o,  into  the  condenser, 
where  it  is  also  at  once  condensed ;  thus  the  process  goes  on, 
until  a  vacuum,  more  or  less  perfect,  depending  upon  the  cold- 
ness of  the  condenser,  is  produced,  not  only  in  the  condenser, 
but  also  extending  into  the  cylinder.  There  being,  therefore,  a 
vacuum  in  the  upper  part  of  the  cylinder,  it  is  evident  that  the 
piston  has  no  atmospheric  column  to  lift,  pressing  with  15 
lb>.  to  the  square  inch,  and  it  need  not,  therefore,  possess 
as  much  expansive  force  by  exactly  this  amount:  hence  its 
name  of  Condensing  and  Low-pressure. 

176.  The  Steam  Engine  in  its  most  complete  form.  In 
the  steam  engine,  in  its  complete  form,  there  is  an  arrangement 
by  which  the  steam  from  the  boiler  can  be  supplied  to  both 
sides  of  the  piston  alternately,  and  then,  having  done  its  work, 

176.  Describe  the  condensing  steam  engine  in  its  most  complete  form.     Show  how  the 
piston  is  made  to  work  in  a  vacuum. 


144 


is  THZ  CO:;DZXSIXG  ENGINE. 

Fi<r.  64. 


T/'ie  Condensing  Steam  Engine. 

be  discharged  from  both  sides  alternately  in'o  the  condenser. 
In  Fig.  63,  the  discharge  pipes  into  the  condenser  are  seen  at 
o  and  c.  Consequently  there  is  always  a  vacu-um  in  the  cyl- 
inder, extending  into  it  from  the  condenser,  on  that  side  of  the 
piston  opposite  to  that  on  which  the  steam  from  the  boiler  is 
pressing;  so  that,  in  moving  in  both  directions,  the  pision  is 
working  in  a  vacuum,  and  the  pressure  of  the  atmosphere  is 
altogether  taken  off.  This  constitutes  the  most  perfect  form  of 
the  steam  engine,  and  is  represented  in  Fig.  64.  A  represents 
the  cylinder,  having  a  portion  of  one  side  removed  to  show  the 
interior,  .s  is  the  pipe,  through  which  steam  enters  from  the 
boiler,  u  is  the  pipe  conveying  the  steam  from  the  cylinder  to 
O,  which  is  the  condenser.  Here  it  is  condeii.  ed  into  water  by 


LATENT    HEAT    OF    THE    CONDENSING    ENGINE.  145 

cold  water  thrown  in  through  the  pipe  T,  by  the  pump  R.  The 
water  thrown  into  the  condenser  for  this  purpose,  and  that  which 
is  formed  by  the  condensation  of  the  steam,  is  drawn  off  by  the 
pump  M,  in  order  that  the  condenser  may  be  prevented  from 
filling,  and  is  discharged  continually  into  the  well  N.  It  is  very 
hot  from  the  latent  heat  given  forth  by  the  condensed  steam, 
and  advantage  is  taken  of  this  by  using  it  to  replenish  the  boiler, 
which  is  done  by  means  of  the  pump  Q.  The  piston,  therefore, 
it  will  be  seen,  works  continually  in  a  vacuum,  and  the  motion 
comniunicated  to  it  is  transmitted  by  means  of  the  working 
beam  L,  and  the  connecting  rod  i,  to  the  crank  K,  by  which  an 
impetus  is  imparted  to  the  fly  wheel  v.  From  the  direction  of 
the  arrows  it  will  be  seen  that  the  piston  is  going  down,  the 
connecting  rod  i  is  going  up,  and  the  fly  wheel  is  turning  towards 
the  left.  The  non-condensing  or  high  pressure  engine  resem- 
bles the  above,  exactly,  except  in  the  omission  of  the  apparatus 
beneath  the  upper  plate,  viz.,  the  condenser  o,  the  pumps  M 
and  R.  The  pump  Q  is  retained  to  feed  the  boiler.  The  pipe 
u,  instead  of  continuing  to  o,  is  broken,  turned  upwards,  and 
discharges  steam  by  puffs  into  the  air. 

177.  Latent  Heat  of  the  Condensing  Engine.  It  is  evident 
from  the  principles  laid  down  above,  that  the  condensation  of 
this  large  amount  of  steam  is  attended  by  the  giving  out  of  the 
enormous  quantity  of  latent  heat  which  it  contains,  viz.,  1000°, 
which  has  a  tendency  to  heat  the  condenser  very  hot,  and  to 
impair  its  efficiency.  It  is  evident,  al  o,  that  if  the  conden-er 
becomes  heated  to  212°,  no  more  steam  can  be  condensed. 
To  prevent  it  from  becoming  thus  heated,  a  great  quantity  of 
cold  water  must  be  used.  The  condensing  engine  can  not, 
therefore,  be  employed  except  where  a  large  amount  of  cold 
water  can  readily  be  obtained.  It  is  unfi'.ted,  therefore,  for  ine 
in  locomotives.  In  con-equence  of  the  additional  size  of  the 
engine  and  the  larger  amount  of  machinery  requiredjt  can  nut 
be  employed  in  confined  situatroin  of  limited  extent,  and  in 
steamboats  on  shaUow  waters.  The  magnificent  marine  engines 
of  ocean  steamers  are,  however,  always  condensing  engines,  and 
so  also  are  the  ponderous  engines  used  for  draining  mines  and 
pimping  water  for  aqueducts.  The  Cornish  steam  engine  is  a 
peculiar  form  of  the  steam  engine  used  in  the  mines  of  Corn- 
wall, for  the  purpo  e  of  raising  water. 

177    Explain  the  large  amount  of  heat  set  free  by  the  condensation  of  the  steam  in  the 
condensing  engine. 

7 


146 


THE    BOILER. 


178.  The  Boiler.  The  steam  engine  consists  of  two  parts, 
quite  distinct  from  each  other:  1st,  the  machinery,  by  which 
the  power  is  made  to  produce  motion  ;  (this  has  been  already  de- 
scribed,) and  2d,  the  apparatus  in  which  the  power  it;  elf  is  gene- 
rated. The  Boiler  is  the  instrument  for  the  production  of  power. 
It  consists  of  a  strong  copper  or  iron  vessel,  Fig.  65,  made  of 


Fig.  65. 


Boiler  of  Steam  Engine. 

well  rolled  plates  of  metal  strongly  riveted  together.  Usually 
it  is  cylindrical  in  shape,  and  if  possible,  the  fire  box  containing 
the  coals,  and  the  flues  by  which  the  smoke  is  carried  off,  are 
contained  within  the  boiler,  in  order  that  every  particle  of  heat 
generated  may  go  to  the  production  of  steam.  The  steam,  as 
it  is  formed,  collects  in  the  upper  part  of  the  boiler,  and  fresh 
portions  being  continually  added  to  it,  all  of  which  tend  to 
occupy  a  space  1700  times  greater  than  the  water  from  which 
they  are  formed,  it  is  obvious  that  its  tension  is  steadily  increas- 
ing, and  a  very  powerful  pressure  exerted  upon  the  water  and 
the  sides  of  the  boiler.  The  temperature,  at  the  same  time, 
steadily  rises,  and  if  there  be  no  opportunity  for  the  steam  to  es- 
cape, the  boiler  will  finally  explode.  To  prevent  such  a  catasfro- 
phe,  a  safety  valve  is  provided ;  see  s  v  in  Fig.  65.  This  consists 
of  a  small  piece  of  iron  or  brass  fitting  tightly  over  an  aperture 
in  the  top  of  the  boiler,  and  confined  in  its  place  by  a  heavy 
weight.  So  long  as  the  steam  exerts  a  less  pressure  upon  the 
under  side  of  the  movable  plug,  than  the  weight,  it  will  remain 

.  178.  Into  what  two  distinct  parts  may  the  steam  engine  be  divided  ?  Describe  the  con- 
struction and  arrangement  of  the  boiler. 


STEAM    MUST    BK    COMPRESSED  147 

in  its  place,  and  the  steam  can  not  escape ;  but  whenever  it  has 
accumulated  to  such  a  degree  as  to  press  upon  the  plug  with  a 
power  greater  than  the  weight,  it  will  raise  it,  and  escape  into  the 
air,  until  the  pressure  in  the  inside  is  made  equal  to  the  pressure 
on  the  outside.  Usually,  this  movable  plug  is  kept  in  its  place 
by  a  lever,  from  one  end  of  which  the  weight  is  suspended. 
This  may  be  seen  at  5  v,  in  Fig.  65  ;  also,  at  A,  in  Fig.  71.  The 
pressure  in  the  interior  may  be  measured  by  means  of  the  mer- 
curial gauge  that  has  been  described  in  the  account  of  Marcet's 
apparatus,  (§1 68,)  or  by  others  depending  on  different  principles. 
By  the  operation  of  the  safety  valve,  and  a  careful  observation  of 
the  gauges,  the  danger  of  explosion  is  guarded  against.  When 
the  temperature  of  the  water  has  risen  to  250°  there  is  a  pressure 
of  30  Ibs.  to  the  square  inch  in  the  interior  of  the  boiler ;  when 
itjias  mounted  to  275°,  there  is  a  pressure  of  45  Ibs. ;  at  294°, 
a  pressure  of  60  Ibs.,  &c. ;  but  as  the  atmospheric  pre-sure  on 
the  outside  of  the  boiler,  tending  to  bind  its  plates  more  firmly 
together,  amounts  to  15  Ibs.  on  every  square  inch,  the  actual 
internal  pressure  tending  to  burst  the  boiler,  or  the  working 
power  of  the  steam,  is  the  excess  of  the  total  pressure  over  15 
Ibs.,  and  is  found  by  subtracting  15  from  the  number  indicating 
the  total  pressure.  The  explosive  force  for  250°  is,  therefore, 
15  lb>. ;  for  275°,  30  Ibs.;  294°,  45  Ibs.  This  fact  must  be 
constantly  borne  in  mind  in  all  calculations  upon  the  pressure 
upon  the  inside  of  boilers.  The  steam,  when  formed,  collects 
in  the  upper  part  of  the  boiler,  and  is  conveyed  to  the  cyl- 
inder by  the  pipe  £  which  is  commanded  by  a  stop-cor-k,  under 
the  control  of  the  engineer;  #  is  a  pipe  for  supplying  the  boiler 
with  water ;  n  is  an  opening  by  which  it  may  be  entered  and 
cleansed  ;  b  is  a  lower  portion  of  the  boiler,  communicating  with 
the  upper  by  means  of  the  tubes  P  p  P,  and  intended  to  facili- 
tate the  production  of  steam  ;  c  is  the  fire  box ;  r  the  grate ; 
the  course  of  the  smoke  and  flame  is  indicated  by  the  arrows ; 
after  passing  beneath  the  lower  boiler,  they  circulate  around  the 
upper,  and  finally  escape  by  the  chimney  c,  commanded  by  the 
damper  R.  The  locomotive  boiler,  as  will  be  seen  presently, 
is  arranged  upon  a  somewhat  different  plan. 

179.  The  Boiler  is  not  only  an  instrument  for  converting 
water  into  vapor,  but  also  for  compressing-  this  vapor.  In 
order  to  obtain  any  mechanical  power  from  steam,  it  is  not  suffi- 
cient simply  to  convert  the  water  into  vapor ;  if  this  be  all  that 

179.  How  is  the  requisite  compression  of  the  vapor  formed  in  the  boiler  effected  ? 


148         IN    ORDEK    TO    PRODUCE    MECHANICAL    POWER. 

is  done  the  steam  would  have  no  more  mechanical  power  than 
an  equal  volume  of  air  of  the  same  temperature  :  all  that  would 
have  been  accomplished  would  have  been  to  convert  water  into 
an  aeriform  fluid,  no  more.  In  order  to  obtain  any  mechanical 
power  from  steam,  it  must  be  compressed,  just  as  in  the  ca*e  of 
air.  If  we  wish  to  make  use  of  the  elasticity  of  air  as  a  moving 
power,  we  must  compress  it  by  powerful  forcing  pumps  ;  a  large 
quantity  of  air  is  thus  packed  into  a  small  space,  and  as  it  tends 
to  return  to  its  original  volume  in  consequence  of  its  elasticity, 
it  is  evident  that  we  have  here  a  very  considerable  source  of 
power.  In  the  same  way,  if  we  wish  to  obtain  power  from 
steam,  we  must  compress  it,  and  at  the  same  time  elevate  its 
temperature.  Both  these  conditions  are  requisite.  If  steam 
be  compressed  without  any  addition  to  its  temperature,  a  portion 
is  reconverted  into  water,  and  its  elastic  force  remains  un- 
changed ;  if,  however,  it  be  powerfully  compressed,  and  at  the 
same  time  elevated  in  temperature,  its  elastic  force  is  enor- 
mously increased.  This  will  be  made  more  clear  hereafter. 
These  conditions  being  preserved,  the  more  powerfully  it  is 
compressed,  the  more  violently  does  it  tend  to  return  to  its  orig- 
inal volume.  The  only  difference  is,  that  instead  of  compress- 
ing the  steam  by  pumps,  we  do  it  by  forming  more  and  more 
steam  from  the  water  within  the  boiler,  and  every  fresh  forma- 
tion more  forcibly  compresses  that  which  existed  before,  and 
proportionably  increases  its  elasticity.  This  soon  generates  an 
enormous  power,  which  not  only  endangers  the  boiler,  but  also 
reacts  upon  the  water,  and  tends  to  stop  the  formation  of  addi- 
tional steam ;  to  overcome  this  tendency  the  temperature  must 
be  steadily  elevated.  It  is  therefore  by  increasing  the  heat  that 
the  expansive  power  of  steam  is  augmented ;  but  the  two  do 
not  increase  at  an  equal  rate ;  the  power  increases  much  faster 
than  the  temperature,  and  when  we  reach  very  high  tempera- 
tures, such  as  400°  ;  an  addition  of  4°  or  5°  to-the  temperature 
of  the  boiler  adds  as  much  to  the  elastic  power  of  the  steam  as 
40°  added  to  it  at  the  temperature  of  212°V  It  will  be  observed 
that  for  this  process  to  go  on,  there  must  be  a  continued  supply 
of  water  in  the  boiler;  if  the  water  has  all  boiled  away  then 
the  steam  is  only  increased  in  volume  by  the  increase  of  tem- 
perature, at  the  same  rate  as  so  much  air  would  be,  i.  e.,  for  1  °, 
^.J^  of  the  space  it  occupied  at  32°.  The  steam  being  thus 
formed  and  thus  compressed,  tends  to  rush  forth  with  great  fury. 
It  presses  upon  all  areas  of  the  boiler  of  equal  size,  with  equal 


MODE    IN    WHICH   PRESSURE    IS  149 

power,  and  if  a  section  of  the  boiler  were  movable,  it  would 
press  it  steadily  outward. 

180.    Law  of  the  Propagation  of  Pressure  through  Fluids. 
This  equal  distribution  of  pressure  is  owing  to  the  law  of  the 
propagation  of  pressure  through  fluids,  both  in  the  state  of 
liquids  and  in  that  of  vapors  or  gases,  viz.,  that  a  force  applied 
to  a  fluid  at  one  point,  is  propagated  through  it  equally  in  all 
directions.     This  is  illustrated  in  Fig. 
Fig.  66.  66,  where  a  closed  vessel  being  en- 

tirely filled  with  water,  and  having  a 
number  of  pistons  pressed  down  upon 
the  liquid  on  all  sides,  and  there  being 
two  weights  of  five  pounds  each  or  a 
force  of  10  Ibs.  applied  upon  the 
piston  A,  this  pressure  of  10  Ibs.  is 
propagated  equally  in  all  directions, 
and  every  one  of  the  other  pistons,  B, 
C,  D,.  E,  having  an  equal  area,  tends  to 
move  outwardly  wiih  the  same  force, 

Pressure  Propagated  in  Fluids.      VIZ.,     10    Ibs.       The     Same     would    be 

true  if  the  vessel  were  filled  with  air, 

or  any  other  aeriform  fluid,  like  steam.  Nor  does  it  make  any 
difference  whether  the  internal  pressure  be  produced  from  with- 
out as  in  Fig.  66,  or  from  within  by  internal  expansion,  as  it 
would  be  if  this  water  were  converted  into  steam,  occupying 
1700  times  more  space  than  before.  In  any  case  the  pressure 
which  is  exerted  upon  any  area  of  the  inside  surface  of  the 
boiler,  as  a  foot  square,  for  example,  will  be  exerted  to  an  equal 
degree  upon  every  other  area  of  equal  size.  Nor  does  the 
shape  of  the  vessel  make  any  difference,  however  irregular  this 
shape  may  b3.  If  a  tube  be  carried  from  one  vessel  to  another, 
at  some  distance,  so  long  as  this  tube  is  open  and  the  passage 
free  from  obstruction,  the  pressure  upon  any  definite  area  in  the 
first  vessel  will  be  propagated  through  the  fluid  in  the  tube, 
whether  it  be  liquid  or  vapor,  and  be  exerted  to  the  same  deirivo 
upon  every  equal  area  in  the  second  vessel.  Consequently  if 
there  be  a  pressure  of  60  Ibs.  to  the  square  inch  at  one  point  of 
the  internal  surface  of  a  boiler,  there  is  the  same  pressure  to 
the  square  inch  at  every  other  point  in  the  boiler,  or  in  any  closed 
vessel  connected  with  the  boiler  by  an  open  tube  or  pipe. 


180.  State  the  law  of  the  propagation  of  pressure  through  fluids. 


150    TRANSMITTED  FROM  THE  BOILER  TO  THE  CYLINDER. 


Fig.  67. 


Pressure  transmitter]  from  Boiler 
to  Cylinder. 


181.  Mode  in  which  the  Pressure  is  transmitted  from  the 
Boiler  to  the  Cylinder.    On  attaching  to  the  upper  part  of  the 

boiler,  B,  a  tube  leading  to  the  bot- 
tom of  a  cylindrical  chamber,  in 
which  there  is  a  movable  piston,  as 
is  represented  in  Fig.  67,  it  is  evi- 
dent that  the  steam  will  at  once  fill 
the  tube ;  the  cylinder  c  will  be- 
come a  part  of  the  boiler,  and  the 
steam  will  press  upon  the  lower 
side  of  the  piston  r  with  the  same 
force  precisely  as  upon  an  equal 
area  of  the  boiler.  If  the  steam 
exert  a  pressure  in  the  boiler  of 
GO  Ibs.  to  the  square  iuch,  it  will 
exert  the  same  pressure  in  the 
cylinder.  If  the  piston  in  the  cyl- 
inder have  a  we'ght  upon  it,  which 

presses  it  down  \vith  the  force  of  GO  Ibs.  to  the  square  inch,  it  will 
not  be  moved  from  its  position;  but  if  it  be  pressed  by  a  weight 
less  than  60  Ibs.  to  the  square  inch,  it  will  be  driven  to  the  top 
of  the  cylinder.  If,  when  it  has  reached  this  point,  the  steam 
through  another  pipe  be  brought  to  bear  upon  its  upper  side, 
while  at  the  same  time  it  is  shut  off  from  the  lower  side,  and 
the  steam  confined  there,  be  let  off  into  the  air,  it  is  evident  that 
the  piston  will  be  driven  down  again  with  the  same  force  as 
it  was  driven  up.  The  piston,  then,  may  be  looked  upon  as  a 
movable  section  of  the  boiler,  which  is  alternately  driven  up  and 
down  by  the  steam  admitted  upon  its  under  and  upper  side ; 
and  if  machinery  be  attached  to  this  movable  piston,  it  will  par- 
ticipate in  its  motion, 

182.  Explosion  of  Steam  Boilers.    A  boiler  like  that  repre- 
sented in  Fig.  65,  if  made  of  good  materials,  may  be  gradually 
heated  to  a  degree  much  higher  than  212°,  without  any  Tagger 
of  bursting,  so  long  as  the  engine  is  working  and  the  water 
covers  all  the  parts  which  are  exposed  to  the  direct  action  of 
the  flame,  because,  under  these  circumstances,  no  portion  of  the 
boiler  can  be  heated  hotter  than  the  temperature  of  the  wa'er 
itself.     But  if  the  water  should,  from  any  cause,  fall  so  low 
that  some  of  the  parts  exposed  to  the  flame  should  have  no 

181.  How  is  the  pressure  transmitted  from  the  boiler  to  the  cylinder?  Why  may  the 
piston  be  regarded  as  a  movable  section  of  the  boiler? — 182.  What  is  the  cause  of  the 
explosion  of  steam  boilers,  and  how  may  they  be  prevented? 


THE    EXPLOSION    OF    BOILERS.  151 

water  upon  the  inside  to  keep  them  cool,  these  might  become 
red-hot,  and  when  the  boiler  was  replenished  with  water,  this 
coming  into  contact  with  the  red  hot  iron,  would  instantly  pro- 
duce a  vast  volume  of  steam  of  immense  expansive  power,  and 
before  it  could  raise  the  safety  valve  and  escape,  the  boiler 
would  explode.  Such  accidents  are  very  likely  to  happen 
immediately  upon  setting  an  engine  in  motion,  after  stopping 
it  for  a  short  time.  During  this  interval  of  quiet,  the  water 
steadily  boiling  away,  and  its  level  falling,  may  at  length  sink 
below  the  top  of  the  flues,  and  a  portion  of  the  boiler  become 
heated  very  hot,  no  water  being  forced  in  to  supply  the  place  of 
that  which  is  evaporated,  in  consequence  of  the  stoppage  of  the 
pumps.  If,  at  the  same  time,  the  safety  valve  be  shut,  the  steam 
formed  will  react  upon  the  surface  of  the  water  with  so  much 
force  as  finally  to  stop  the  ebullition,  and  keep  its  surface  per- 
fectly quiet,  but  still  with  a  constantly  increasing  tendency  to 
boil  with  vehemence,  as  we  have  seen  illustrated  in  the  steam 
flask,  (§  1G7.)  Now,  under  these  circumstances,  let  this  press- 
ure be  removed  by  the  starting  of  the  engine.  The  water  will 
recommence  boiling  with  so  much  fury  that  it  will  be  clashed 
ag  linst  the  top  of  the  boiler,  and  coming  into  contact  with  the 
too  highly  heated  portions,  it  will  flash  into  steam  of  such  ex- 
pansive power  that  nothing  can  control  it,  and  an  explosion  will 
result.  Or,  suppose  that,  the  water  boiling  away,  and  the  boiler 
becoming  too  hot,  the  safety  valves  at  first  are  opened,  so  that 
the  steam,  as  fast  as  formed,  escapes,  and  the  boiling  is  not 
checked  as  before,  and  afterwards,  at  the  instant  of  starting,  that 
these  valves  are  closed ;  then  the  pumps  beginning  to  work  at 
the  same  time  with  the  engine,  speedily  bring  up  the  level  of 
the  water  to  the  too  highly  heated  iron,  and  an  explosion  resulis 
as  before.  It  is  a  point,  therefore,  of  the  first  importance,  for 
the  engineer  to  keep  a  vigilant  eye  upon  the  level  of  the  water 
in  the  interior  of  the  boiler.  This  may  be  observed  by  having 
stop-coL'ks  at  different  levels,  which  from  time  to  time  must  be 
opened  to  ascertain  if  they  discharge  water  or  steam ;  or  by  a 
curved  tube  of  glass,  connected  with  the  boiler,  in  such  a  way 
as  to  show  the  height  of  the  water.  See  o,  in  boiler,  Fig,  120. 
There  are  other  means  by  which  the  same  end  may  be  at- 
tained. Let  s,  in  Fig.  65,  represent  a  steam  whistle,  which  can 
be  made  to  sound  by  pulling  a  wire  from  bebw,  attached  to  the 
float,/,  and  let  it  be  arranged  in  such  a  way  that  when  the  float 

Whv  is  it  necessary  te  keep  a  vigilant  eye  upon  the  height  of  the  water  in  the  boiler? 
Hosv  may  this  be  ascertained  ? 


152 


THE    BOILERS    OP    LOCOMOTIVES. 


has  sunk  to  a  certain  fixed  point  it  will  sound  the  whistle,  then, 
whenever  the  water  in  the  boiler  has  declined  so  far  as  to  en- 
danger its  safety,  the  float  descending  with  it  will  open  the 
whistle,  and  sound  the  alarm.  Again,  let  e  be  a  weight,  attached 
to  a  cord  passing  over  a  pulley,  and  descending  through  (he 
upright  pillar,/,  until  it  enters  the  boiler  and  is  attached  to  the 
float,/;  as  the  float  falls  from  the  gradual  sinking  of  the  water, 
it  draws  the  weight  up,  and  being  placed  in  full  view  of  the  en- 
gineer, indicates  the  danger  within. 

183.  Boilers  of  Locomotives.  The  boilers  of  locomotives  are 
constructed  somewhat  differently  from  others.  One  peculiarity 
of  the  locomotive  consists  in  its  rapid  motion,  and  proportion- 
ably  great  consumption  of  steam.  Four  cylinders  full  of  steam 
are  required  for  every  revolution  of  the  wheels.  The  boiler 
must  therefore  be  constructed  in  such  a  way  as  to  produce 
steam  very  fa^t.  To  this  end  the  fire  box,  D,  Fig.  68,  is  en- 
tirely surrounded  by  water,  soKhat  all  the  heat  produced  is 
obliged  to  go  to  the  formation  of  steam ;  the  flame  and  smoke 
are  then  carried  through  a  large  number  of  small  pipes,  indi- 
cated by  the  arrow  in 
68<  the  figure,  which  pass 

through  the  boiler,  and 
terminate  in  a  chamber 
immediately  beneath  the 
chimney.  These  tubes 
expose  a  very  large 
heating  surface,  and  are 
also  surrounded  by 
water;  all  the  heat  pro- 
duced is  therefore  com- 
pelled to  enter  the  water, 
and  the  formation  of 
steam  is  made  wonder- 
Locomotive  Boiler.  fulI7  rapid.  In  the  fig- 

ure,   E    represents    the 

steam  dome,  from  the  upper  part  of  which  the  steam  is  con- 
veyed to  the  cylinders  through  the  pipe  Fv  In  this  manner  the 
spray  and  water  are  prevented  from  surging  into  the  cylinders. 
.As  the  smallness  of  the  tubes  tends  to  diminish  the  draught,  the 
steam,  after  having  done  its  work  in  the  cylinder,  is  discharged 


183.  Describe  the  boiler  of  the  locomotive. 
How  is  tiie  draught  maintained? 


Why  is  it  necessary  to  make  steam  so  fast* 


THE    ALTERNATING    MOVEMENT  153 

through  a  pipe  directly  into  the  air  chamber  beneath  the  eh'm- 
ney,  and  ru.-hing  violently  upwards,  drives  all  the  air  before  it, 
precisely  as  the  plunger  of  a  pump  would,  if  similarly  situated. 
A  vacuum  ii  consequently  created  behind  it,  in  th3  lower  part 
of  the  chimney  and  air  chamber ;  and  this  must  be  supplie  I  by 
a  rush  of  air  through  the  fire  grate,  the  fire  box,  and  the  tubes. 
The  combustion  is  at  once  increased  arid  made  more  and  more 
vigorous  with  every  puff  of  steam.  In  this  way  a  draught  is 
created  equal  to  that  of  a  chimney  80  or  90  feet  in  height ;  the 
more  rapid  the  movement  of  the  engine,  the  more  powerful  the 
draught,  and  the  more  abundant  the  production  of  steam.  This 
mode  of  increasing  the  draught  by  discharging  steam  into  the 
chimney  is  the  great  improvement  made  in  the  steam  engine 
by  Mr.  Geo.  Stephenson,  by  which  it  was  adapted  for  use  upon 
railroads. 

When  steam  is  discharged  in  jets  through  a  pipe  into  the  lower 
part  of  another  tube,  it  always  tends  to  produce  a  vacuum  below 
it,  and  an  arrangement  of  this  kind  is  often  employed  for  the  pur- 
pose of  ventilation.  Steam  thus  escaping  expands  enormously 
as  it  enters  the  atmosphere,  and  so  much  heat  becomes  latent 
by  this  expansion  that  the  hand  placed  in  the  jet  actually  ex- 
periences a  sensation  of  cold,  even  though  the  temperature  of 
the  steam  may  be  considerably  higher  than  212°.  The  cooling 
effect  is  increased  by  the  rapid  intermixture  with  the  air. 

184.  The  alternating*  movement  of  the  Piston,  how  pro- 
duced.—The  Valves.  It  now  remains  to  consider  the  means  by 
which  the  steam  is  admitted  alternately  above  and  below  the 
piston.  This  is  accomplished  by  means  of  the  valves.  There 
are  many  different  forms  of  valves ;  but  the  simplest,  and  on 
the  whole  the  best  form,  is  the  sliding  valve  represented  at  G, 
Fig.  69.  Upon  the  side  of  the  cylinder  is  fitted  a  chest  through 
which  all  the  steam  which  is  admitted  to  the  piston  must  pass. 
This  is  called  the  steam  chest.  The  object  of  the  valve  is  to 
direct  the  steam  from  the  steam  chest  first  to  one  side  of  the 
piston  and  then  to  the  other,  at  the  same  time  allowing  that  upon 
the  opposite  side  to  escape  either  into  the  open  air"  or  into  the 
condenser.  In  order  to  accomplish  this  end  the  two  tubes  con- 
veying the  steam  to  the  two  ends  of  the  cylinder  are  made  to 
terminate  quite  near  each  o'.her,  as  is  represented  in  Figs.  69 
and  70,  and  over  them  there  is  made  to  slide,  steam  tight,  the 
piece  of  metal,  G,  which  is  moved  by  means  of  the  rod,  E, 

Show  how  steam  can  be  used  for  ventilation. — 184.  Explain  the  mode  in  which  the 
alternating  motion  of  the  piston  is  produced. 

7* 


154 


OF    THE    PISTON. THE    VALVES. 


through  the  steam-tight  packing  box,  B.  When  it  has  slid  over 
one  passage,  it  has  opened  the  other,  and  vice  versa.  In  Fig. 
69,  the  passage,  i,  is  open,  and  the  passage,  H,  is  dosed.  The 
steam  is  consequently  pressing  upon  the  under  side  of  the  pis- 


Fin.  70. 


Valve  driving  Piston  up. 


Valve  driving  Piston  down. 


ton,  and  it  is  rising  to  the  upper  end  of  the  cylinder.  When  it 
reaches  the  top,  the  valve  i.s  moved  by  the  action  of  the  engine 
so  as  to  open  the  passage,  H,  as  in  Fig.  70,  when  the  passage, 
i,  becomes  closed,  and  the  piston  begins  to  descend.  In  this 
manner,  by  moving  this  slide,  the  steam  is  admitted  first  to  one 
side  and  then  to  the  other  of  the  piston. 

The  next  point  is  to  provide  for  the  escape  of  the  steam  from 
the  end  of  the  cylinder  towards  which  the  piston  is  moving,  into 
the  open  air,  or  into  the  condenser.  This  is  accomplished  by 
making  the  under  side  of  the  sliding  valve  hollow,  >o  that,  at 
the  same  time  that  it  cuts  off  the  tube  over  which  it  is  moved 
from  communication  with  the  steam  of  the  steam  chest,  it  furn- 


Describe  the  valves. 


THE    EXPANSIVE    POWER    OF    STEAM  155 

ishes  a  way  of  escape  for  the  steam  in  the  cylinder  into  the 
escape  pipe,  T.  In  Fig.  69,  the  steam  from  H  is  passing  into 
the  escape  pipe,  T,  through  the  under  side  of  the  valve.  In 
Fig.  70,  the  steam  from  I  is  passing  into  the  same  escape  pipe 
through  the  groove  on  the  underside  of  the  valve.  By  this 
simple  contrivance  the  alternate  motion  of  the  piston  is  pro- 
duced. 

185.  Steam  may  be  used  expansively.    When  it  is  desired 
to  make  use  of  the  direct  pressure  of  the  steam  from  the  boiler 
for  a  portion  only  of  the  stroke  of  the  piston,  the  steam  is  shut 
off,  at  the  proper  point,  by  a  cut-oft*  valve.     The  steam  that  has 
been  admitted  into  the  cylinder  having  been  strongly  compressed 
in   the   manner    described   in    §    179,    has    still   great   elastic 
force,  and  tends  powerfully  to  enlarge  its  volume,  and  it  will  con- 
tinue to  urge  the  piston  to  the  end  of  the  cylinder  by  the  action 
of  this  expensive  tendency,  notwithstanding  the  connection  with 
the  boiler  has  been  entirely  broken.     This  is  called  using  steam 
expansively,  and  is  one  of  the  inventions  of  Mr.  "Watt,     The 
cut  off  valve  may  be  arranged  so  as  to  cut-off  the  steam  at  any 
portion  of  the  stroke  of  the  piston,  when  it  has  moved  J,  J,  ^  or 
%  of  the  length  of  the  cylinder.     It  is  obvious  that  the  sooner 
the  connection  with  the  boiler  is  cut  off  the  greater  the  saving 
of  the  steam,  and  the  more  economical  the  working  of  the  en- 
gine.    The  cut-off  is  sometimes  a  separate  valve,  sometimes 
merely  a  modification  of  the  slide  valve.     It  is  capable  of  ad- 
justment by  the  engineer,  according  to  the  work  to  be  performed 
by  the  engine. 

186.  The  expansive  power  of  Steam  increases  with  its 
temperature.    The  expansive  power  of  steam  increases  amaz- 
ingly with  the  temperature  at  which  it  is  formed,  so  that,  if  a 
portion  of  the  material  of  the  boiler,  in  consequence  of  the 
want  of  water,  should  have  become  heated  to  415°  F.,  the  ex- 
pansive force  of  the  steam  produced  would  be  300  pounds  to 
the  square  inch;  or  upon  one  square  foot  43,200  pounds,  more 
than  20  tons.     This  pressure,  however,  must  be  diminished  by 
15   pounds  to  the  square  inch,  because  the  pressure  of  the 
atmosphere  on  all  sides  of  the  boiler  tends  to  counteract  the 
expansive  force  of  the  steam  to  this  extent.     It  is  quite  evident 
that  a  force  of  this  degree  of  power  would  burst  almost  any 
boiler,  however  great  its  strength.     The  following  table,  founded 

185.  What  is  meant  by  using  steam  expansively  ?  What  is  the  advantage  of  cutting 
off  steam? — 186.  What  is  the  effect  upon  the  expansive  power  of  steam  of  increasing  its* 
temperature  ? 


156 


INCREASES    WITH    ITS     TEMPERATURE. 


upon  the  experiments  of  Regnault,  shows  the  increase  in  the 
pressure  of  steam  corresponding  with  the  increase  in  its  tem- 
perature. 

Regnauh's  Table  showing  the  Pressure  of  Steam  at  different  temperatures. 


-i.3  . 

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•3s, 

£ 

£ls 

•<  P, 

1 

212° 

11 

1  50  Ibs. 

364°.2 

7-.  6 

2 

15  Ibs. 

249°.5 

37°.5 

12 

165    " 

371°.l 

6o.9 

3 

30 

27  3°.  3 

23  \8 

13 

180    " 

377^.8 

6^.7 

4 

45 

291°.2 

17°.9 

14 

195    " 

384°.0 

6o.2 

5 

60 

306° 

14°.8 

15 

210    4t 

390°.0 

6^.0 

6 

75 

318^.2 

12°.2 

16 

225 

3950.4 

5o.4 

7 

90 

329  \6 

11°.4 

17 

240 

4(10°.  8 

5o.4 

8 

105 

339^.5 

9'\9 

18 

255 

405  .9 

5°.l 

9 

120 

348^.4 

•8°.9 

19 

270 

410°.8 

.  4\9 

T  > 

135 

356  ~.  6 

8V2 

20 

285 

415°.4 

4°.6 

This  table  corresponds  very  nearly  with  one  constructed 
many  years  since  by  Dulong  and  Arago.  They  made  the 
temperature  of  steam  at  30  atmospheres,  418°. 46;  at  50  atmo- 
spheres, 5 10°. 60.  It  will  be  observed  that  the  number  of  de- 
grees required  to  add  an  additional  atmosphere  is  much  smaller 
at  high  than  at  low  temperatures,  i.  e.,  the  greater  the  pressure, 
and  the  higher  the  temperature,  the  smaller  the  number  of  de- 
grees necessary  to  be  added  in  order  to  increase  the  elasticity 
and  expansive  power  of  the  steam.  Thus,  if  the  steam  be  at  2 1 2°, 
it  is  necessary  to  add  37°. 5  of  heat  in  order  to  increase  its  press- 
ure by  15  Ibs.;  while  if  it  be  at  410°  only  4°.6  are  required.  This 
io  one  of  the  principal  reasons  for  the  increased  economy  of  power 
in  using  steam  at  a  high,  rather  than  at  a  low  pressure. 

187.  No  economy  of  Fuel  in  boiling*  Water  at  a  low  tcm- 
psraturc.  As  wa^er  may  be  made  to  boil  at  a  temperature  of 
70°  in  a  vacuum,  it  has  been  a  question  whether,  by  the  removal 
of  the  atmospheric  pressure  from  the  boiler,  a  £reat  economical 
advantage  might  not  be  gained  in  the  saving  of  fuel.  Mr.  Watt 
ascertained,  by  carefuf  experiment,  that  nothing  is  gained  in 
this  manner,  because  the  lower  the  temperature  at  which  The 
steam  is  formed  the  greater  the  amount  of  latent  heat  which  it  con- 
Give  the  general  results  of  Regnault's  table.— 187.  Why  is  there  no  economy  of  fuel 
hi  boiling  water  at  a  low  temperature?  Who  ascertained  this  fact? 


NO    ECONOMY    IX    FORMING    STEAM 


157 


tains.  Bj  condensing  steam  formed  at  this  temperature,  and 
observing  the  quantity  of  heat  which  it  communicated  to  a  given 
weight  of  water,  he  ascertained  that  its  latent  heat,  instead  of 
being  about  1000°,  was  between  1200°  and  1300°.  It  is  now 
a  well  recognized  principle  that  whatever  be  the  temperature  at 
which  steam  or  vapor  may  be  formed,  the  sum  total  of  the  heat 
contained  in  it,  both  sensible  and  insensible,  is  nearly  the  same. 
Thus,  according  to  the  experiments  of  Clement  and  Desorm^s, 
a  certain  weight  of  steam  at  212°,  condensed  into  water  at  ,32°, 
gave  out, 

Sensible  heat, 180°. 

Latent  heat, 950°.         Total,     1130°. 

The  same  weight  at  250°,  gave  out, 

Sensible  heat, 218°. 

Latent  heat, 912°.         Total,     1130°. 

The  same  weight  at  100°,  gave  out, 

Sensible  heat, 68°. 

Latent  heat, 1062°.         Total,     1130°. 

Consequently,  whatever  the  temperature  at  which  steam  is 
forme  1,  th(3  tolal  amount  of  heat  required  is  nearly  the  same. 
Mr.  Watt  was  of  the  opinion  that  this  was  strictly  true  ;  but 
Regnault  has  shown  that  the  sum  of  the  sensible  and  latent  heat 
increases  as  the  temperature  rises;  the  amount,  however,  is  so 
small  that  it  may  be  neglected  in  practice.  It  will  be  remem- 
biTed  that  the  lower  the  temperature  at  which  water  boils,  the 
greater  the  amount  of  its  expansion  in  passing  into  vapor ;  con- 
sequently, the  greater  the  amount  of  latent  heat  necessary. 

RegnaulCs  Table  showing  the  sum  of  sensible  and  latent  heat  in  steam  al 
different  temperatures : 


Tempera- 
ture. 

Lafent 
Heat. 

Sum  of 
Latent  Heat 
and  Sensible 
Heat. 

Tempera- 
ture. 

Latent 
Heat. 

Sum  of 
Latent  Heat 
and  Sensible 
Heat 

32°       . 

1092°.  6 

1124*.6 

24S° 

939°.  6 

ii87*.« 

5:)° 

Io8i>°.0 

1130°.0 

266° 

927  °.0 

llftfto-.O 

68° 

1067°.4 

11  35°.  4 

284° 

914°.  4 

119S°.4 

86° 

1<>54C.8 

114U°.8 

302° 

901°.8 

12030.8 

104° 

li)42°.2 

1146°.2 

320° 

889J.2 

1209°.  2 

122° 

lu2'J°.G 

1151°.6 

338° 

874°.8 

2i2°.a 

140° 

1017°.  0 

1167°,0 

SoG0 

862°.  2 

2  18°.  2 

158° 

1004o.4 

116'2°.4 

374° 

849°.  6 

2  23°.  6 

176° 

9i)lp.8 

1167°.  8 

392° 

835°.  2 

227°.  2 

194° 

979°.  2 

11  73°.  2 

410* 

822°.  6 

232°.  6 

212- 

9G50.6 

1178°.  6 

428° 

8(>8°.  2 

23<>°.2 

230° 

9o2°.2 

1182°.2 

446° 

795°.  6 

1241<>.6 

How  may  it  be  proved  ?     Give  the  general  results  of  Regnault's  table. 


158  AT    A    LOW    TEMPERATURE. 

188.  No  economy  in  using-  Liquids  which  boil  at  a  lower 
temperature  than  Water.  As  alcohol  and  ether  boil  at  lower 
temperatures  than  water,  it  might  be  thought  that  it  would  be 
economy  to  use  them,  instead  of  water,  as  sources  of  power. 
This,  however,  would  not  be  the  case,  even  though  they  could 
be  procured  for  nothing,  for  two  reasons :  first,  on  account  of 
the  comparatively  small  expansion  of  these  liquids  in  passing 
into  vapor.  A  cubic  foot  of  water  yields  1700  cubic  feet  of 
steam ;  a  cubic  foot  of  alcohol  yields  only  493  cubic  feet  of 
vapor.  It  is  necessary,  therefore,  to  boil  away  more  than  3 
cubic  feet  of  alcohol  in  order  to  make  1700  cubic  feet  of  alco- 
holic vapor  and  create  a  moving  power  equal  to  that  of  steam. 
A  cubic  foot  of  ether  yields  only  212  cubic  feet  of  vapor ;  it  is 
necessary,  therefore,  to  boil  away  8  cubic  feet  of  ether  to  make 
1700  cubic  feet  of  ethereal  vapor.  This  would  require  a  cor- 
responding enlargement  of  the  boiler,  and  many  of  the  other 
parts  of  the  engine.  Secondly,  to  form  1700  feet  of  alcoholic 
and  ethereal  vapor  would  require  more  heat  than  to  form  17(0 
cubic  feet  of  steam.  Thus,  the  latent  heat  of  steam  is  1000°  ; 
the  latent  heat  of  an  equal  volume  of  alcoholic  vapor  is  1575° ; 
the  latent  heat  of  an  equal  volume  of  vapor  of  ether  is  2500°. 
Their  cost  in  fuel  would  be  proportionate  to  the  sum  of  the 
sensible  and  latent  heat  of  equal  volumes ;  it  is  evident,  there- 
fore, that  the  advantage  would  be  decidedly  on  the  side  of  water. 
This  may  be  clearly  seen  from  the  following  table : 

TJte  Latent  Heat  contained  in  equal  volumes  of  Water,  Alcohol,  Etlier, 

and  Spirits  of  Turpentine : 

A  cu.  ft.  of  Water  yields  1700  cu.  ft.  of  Steam,  latent  heat, ....  1000°. 
A  cu  ft.  of  Alcohol  yields  493  cu,  ft.  of  Vapor,  latent  heat,  457°. 

493  cubic  feet:  457°: :  1700  cubic  feet:  x°— 1575°. 

A  cu.  ft.  of  Ether  yields  212  cu.  ft.  of  Vapor,  latent  heat,  312°. 

212  cu-bic  feet:  312J::  1700  cubic  feet: -x°= 2500°. 

A  cu.  ft.  of  Spts.  Turp.  yields  192  cu.  ft.  of  Vapor,  latent  heat,  183°. 

192  cubic  feet:  183 3: :  1700  cubic  feet:  x  — 1620°. 

The  heat,  therefore,  required  to  produce  an  equal  amount  of 
mechanical  power  from  water,  alcohol,  ether,  and  spirits  of  tur- 
pentine, is  as  1000°  to  1575°  to  2500°  to  1620°. 

189.    Super-heated  Steam.  Steam  which  receives  an  acces- 
sion of  heat .  after  it  has  been  separated  from  the  water  that 

188.  Why  is  there  no  economy  in  using  liquids  which  boil  at  a  lower  temperatme  iVi.m 
•water?  Show  this  from  the  table  in  the  case  of  alcohol,  ether,  and  spirits  of  turpentme. 
—189.  What  is  meant  by  super-heated  steam  ? 


PAPIN'S  DIGESTER.  159 

formed  it,  by  passing  through  a  series  of  hot  pipes,  acquires 
some  important  properties  which  distinguish  it  from  ordinary- 
steam.  In  the  first  place,  it  has  more  expansive  power,  and 
this  may  be  imparted  to  it  without  any  additional  expenditure 
of  fuel.  Secondly,  it  is  not  so  readily  condensed  as  common 
steam ;  ordinary  steam  returns  at  once  to  the  liquid  state  as 
soon  as  its  temperature  is  at  all  reduced ;  but  in  the  case  of 
super-heated  steam  no  part  of  it  can  return  to  the  liquid  state 
until  it  lose  all  the  heat  which  has  been  imparted  to  it  by  the 
super-heating  process.  For  this  reason  super-heated  steam  is 
often  employed  in  high-pressure  steam  engines,  in  which  it  is 
considered  important  to  prevent  the  condensation  of  the  steam  as 
much  as  possible  during  its  progress  through  the  cylinder ;  in 
this  manner  all  condensation  is  avoided  until  the  steam  has  been 
allowed  to  escape  into  the  air.  It  is  formed  by  causing  the 
steam,  after  it  has  been  made  in  the  boiler,  to  pass  through  a 
series  of  very  hot  tubes  before  it  is  allowed  to  enter  the  cylinder. 
199.  Papin's  Dig-ester.  The  solvent  powers  of  water  are 
greatly  increased  by  the  high  temperature  which  may  be  given 
to  it  by  boiling  it  under  great  pressure.  At  the  pressure  of 
two  atmospheres,  or  30  pounds  to  the  square  inch,  the  tempera- 
ture of  water  is  250° ;  at  three  atmospheres,  275°.  This  in- 
creased solvent  power  is  turned  to  good  account  in  Papin's 
Dige.-ter,  which  consists  of  a  very  strong  metallic  vessel,  upon 
which  the  lid,  C,  fits  steam  tight  and  is  confined  by  a  powerful 
screw ;  a  safety  valve  is  provided  to  prevent  explosion.  The 
water  and  the  substances  to  be  dissolved  must  be  introduced 
before  the  top  is  screwed  down.  By  this  instrument  gelatine 
and  albumen  have  been  extracted  from  bones  and  applied  to  the 
formation  of  various  valuable  products.  These  bones  might  be 
boiled  at  the  temperature  of  212°  for  an  indefinite  period,  without 
change.  This  apparatus  is  of  the  greatest  utility  for  boiling 
vegetables  and  meats  at  points  of  great  elevation,  where  the 
pressure  of  the  atmosphere  is  so  low  that  the  heat  of  water  at 
the  boiling  point  is  not  sufficient  for  cooking.  By  enclosing 
these  articles  .in  a  vessel  of  this  description  the  heat  may  be  in- 
creased to  the  required  degree  without  the  slightest  difficulty. 
On  the  same  principle,  the  cooking  of  vegetables  at  ordinary 
levels  may  be  quickened  by  covering  the  pot  containing  them 
with  a  lid  firmly  held  in  its  place  by  a  few  bricks.  Steam, 
heated  to  a  high  temperature  by  passing  through  red-hot  pipes, 
rnay  also  be  used  for  the  same  purpose ;  and  for  converting 

190.  Describe  tii«  construction  and  use  of  Papin's  digester. 


ICO 


THi:    SPHEROIDAL    STATE. 

ig.  n 


Papin^s  Digester. 

wood  into  charcoal  by  driving  off  all  the  volatile  portions,  leav- 
ing the  pure  carbon  behind ;  also  for  the  distillation  of  oil>%  and 
the  extraction  of  lard  and  fat  from  the  bodies  of  animals.  Steam 
may  be  heated  hot  enough  to  melt  lead  and  to  set  wood  on  fire. 
191.  The  Spheroidal  State.  Though  heat  is  the  cause  of 
ebullition,  and  a  sufficient  amount  of  it  would  no  doubt  produce 
the  vaporization  of  the  most  refractory  substances,  yet  a  high 
degree  suddenly  applied  to  liquids  vaporizes  them  more  slowly 
than  a  lower  degree.  Water  thrown  on  a  plate  of  iron,  or  sil- 
ver, heated  to  redness,  instead  of  instantly  flashing  into  steam, 
rolls  upon  its  surface  in  globules,  and  is  a  long  time  in  disap- 
pearing. This  is  occasioned  by  an  atmosphere  of  vapor  that  is 
at  once  formed  around  the  globules  of  water,  which,  being  a 
poor  conductor  of  heat,  cuts  it  off  from  the  action  of  the  hot 
plate,  and  by  its  elasticity  actually  interposes  a  cushion  between 
them  and  elevates  the  globule  slightly  above  the  plate.  This 
elevation  of  the  drop  above  the  plate  is  perceptible  by  the  eye. 
The  apparatus  for  showing  this  is  represented  in  Fig.  72. 

191.  Explain  the  spheroidal  state. 


THE    SPHEROIDAL    STATE    EXPLAINS 


161 


Fig.  72. 


Space  between  the  Hot  Plate  and  the  Drop. 


A  lamp,  called  an  eolopile,  is  mounted  upon  a  foot,  provided 

with  screws,  so  that  it 
may  be  adjusted  to  an 
exact  level.  Immedi- 
ately over  it  is  placed  a 
smooth  plate  of  silver, 
which  is  heated  red-hot 
by  the  inflammation  of 
the  alcohol  in  the  eolo- 
pile. In  the  middle  of 
this  plate  is  placed  a  hol- 
low cylinder,  open  at 
both  ends,  also  of  silver, 
and  having  a  longitudi- 
nal slit  on  two  opposite 
sides,  at  equal'distances  from  each  other.  Three  or  four  grains 
of  water,  blackened  by  lamp-black,  are  then  poured  into  the 
cylinder,  and  its  top  is  covered  by  a  small  disk  of  metal.  The 
water  is  immediately  thrown  into  the  spheroidal  state,  and  if  a 
candle  be  placed  directly  opposite  to  the  slit  on  one  side,  and 
the  eye  applied  to  the  other,  it  will  be  seen  that  the  water  does 
not  rest  upon  the  hot  plate,  but  is  supported  above  it.  The 
electric  spark  can  also  be  seen  through  the 
same  interval,  between  the  plate  and  the 
drop.  Thus  situated,  water  is  said  to  be 
in  the  spheroidal  state,  from  the  spheroidal 
form  it  assumes  in  rolling  upon  the  red-hot 
plate.  The  apparatus  for  performing  these 
experiments  is  represented  in  Fig.  73. 
The  red-hot  capsule  of  silver  or  copper 
may  be  filled  nearly  full  of  water  without 
its  boiling,  and  if  a  thermometer  be  dexter- 
ously introduced,  the  temperature  will  be 
found  to  be  about  205°,  instead  of  212°. 
Under  similar  circumstances  the  tempera- 
ture of  alcohol  is  168°,  instead  of  170°,  its 
boiling  point;  ether  93°,  instead  of  96°; 
sulphurous  ac'd  only  13°,  considerably  be- 
1  >w  the  freezing'point  of  water.  For  water 
to  pa<s  into  this  state  it  is  necessary  that 

Temperature   of  \V,it,r  m      i  i     ,  A    •        i     i        A 

spheroidal  siate.        tne  plate  or  capsule  have  attained  the  tem- 
perature of  at  least  340°.     If  at  this  mo. 

Describe  the  experiments. 


Fig.  73. 


205" 


1C2 


THE    EXPLOSIONS    OF    BOILERS,    ALSO 


Fig.  74. 


Fig.  75. 


ment  the  red-hot  capsule,  nearly  full  of  water,  be  quickly  and 
carefully  removed  from  the  flame  and  placed  upon  a  tripod 
stand,  it  gradually  cools,  and  the  water  being 
less  and  less  repelled,  at  length  comes  into 
direct  contact  with  the  metal,  bursts  into 
steam  with  explosive  violence,  and  is  project- 
ed in  all  directions,  affording  an  excellent 
illustration  of  increased  activity  of  ebullition 
produced  by  diminution  of  temperature,  Fly. 
74.  Even  if  the  water  be  boiling,  its  tem- 
perature sinks  from  5°  to  7°  below  the  boiling 
point  at  the  moment  it  falls  on  the  healed 

The  Lamp  Removed,    surface,  i.  6.,  from  212°  to  207°. 

192.    It  explains  the  explosions  of  Steam 

Boilers.    If  a  copper  flask  be  heated  red-hot   by  a  powerful 
lamp,  a  large  quantity  of  water  may  be  introduced  "into  it  through 

a  fine  tube,  without  its  boiling,  and 
a  cork  securely  fitted  to  its  mouth. 
If  now  the  lamp  be  extinguished,  as 
the  fla-k  cools,  the  water  at  length 
comes  into  contact  with  the  metal, 
flashes  into  steam,  and  the  cork  is 
driven  out  with  great  fury.  This  is 
thought  by  some  to  be  the  state  of 
things  in  the  interior  of  steam  boil- 
ers when  explosions  are  produced 
by  diminishing  the  heat  of  the  fire ; 
Fig.  75. 

On  the  same  principle  a  red-hot 
copper  ball  may  be  introduced  into 
water  at  the  temperature  of  75°, 
and  remain  visibly  red-hot  for  a  few 
seconds.  The  vapor  of  steam  which 
surrounds  the  ball  for  a  time  pre- 
vents the  contact  of  the  fluid ;  Fig. 
76.  As  soon  as  the  ball  has  suffi- 
ciently cooled,  the  water  ceases  to  be 
repelled  by  the  envelope  of  steam,  and  coming  into  contact  with 
tiie  hot  copper,  is  at  once  converted  into  steam,  scattering  the 
liquid  in  every  direction  ;  Fig.  77. 

192.  Show  how  it  may  explain  the  explosions  of  boilers.  Explain  the  red  heat  of  a 
copper  ball  under  water.  Show  how  water  and  mercury  may  be  frozen  in  a  red  hot  cru- 
cible. 


Explosion  of  Boiler. 
Lamp  Extinguished. 


THE    RED    HEAT    OF    METALS    UNDER    WATER.  1G3 

Fisr.  76. 


Ball  of  Copper  Red-hot  under  Water. 
Fiff.   77. 


Red-hot  Ball  Cooled. 


On  the  same  principle  the  human  hand,  moistened  w'tli  water, 
may  be  d'.pped  with  impunity  into  a  vessel  o/  melted  lead,  or 


164 


DISTILLATION. 


iron,  the  vapor  that  is  formed  by  the  moisture,  for  a  certain 
length  of  time,  keeping  off  the  melted  metal.  In  pouring  glass 
into  wooden  moulds  it  is  usual  to  introduce  first  a  small  portion 
of  water.  Bypassing  into  the  spheroidal  state  it  is  repelled 
from  the  glass,  so  that  it  does  not  injuriously  cool  it,  and  at  the 
same  time  protects  the  wood.  In  performing  these  experiments, 
provided  the  hot  surface  be  a  sufficiently  good  conductor  of  heat, 
the  nature  of  the  material  is  unimportant.  Silver,  platinum, 
copper  and  iron,  may  all  be  used.  One  liquid  may  be  thrown 
into  the  spheroidal  state  upon  the  surface  of  another,  as  water, 
alcohol,  or  ether,  on  the  surface  of  hot  oil.  Solids  can  also  be 
thrown  into  the  spheroidal  state  by  being  placed  on  hot  plates, 
as  iodine  on  hot  copper.  The  iodine  is  melted  and  thrown  into 
the  spheroidal  state,  emitting  but  little  vapor ;  but  if  the  lamp 
be  removed  so  as  to  permit  the  capsule  to  cool,  it  suddenly  bursts 
into  a  magnificent  cloud  of  rich  violet  vapor.  Liquefied  sul- 
phurous acid  passes  into  the  spheroidal  state  at  13°,  notwith- 
standing it  is  in  the  interior  of  a  red-hot  crucible.  If  a  drop 
of  water  be  introduced  into  the  acid,  under  these  circumstances, 
it' is  instantly  frozen.  Solidified  carbonic  acid  and  ether  pa-s 
into  the  spheroidal  state  at  so  low  a  temperature  that,  if  a  globule 
of  mercury  be  introduced  into  the  mixture,  it  is  immediately 
solidified,  and  may  be  turned  out  solid  upon  the  table. 

193.   Distillation.     The   difference    between    the   boiling 


Fig.  78 


Distillation  of  Water. 


LIEBIG'S  CONDENSING  TUBE. 


165 


points  of  liquids  is  sometimes  made  use  of  to  separate  them 
from  each  other,  and  to  clear  them  of  impurities.  This  pro  e  s 
is  called  distillation.  It  consists  in  raising  liquids  in'.o  vapor  by 
boiiing,  and  then  condensing  the  vapor  by  causing  it  to  come 
in  o  contact  with  some  cold  surface.  This  is  usually  accom- 
plished by  having  a  tube  of  considerable  length  leading  from 
the  top  of  a  closed  boiler  and  passing,  in  the  form  of  a  spiral, 
through  a  vessel  which  is  kept  filled  with  cold  water,  changed 
as  fa  4  as  it  becomes  warm ;  Fig.  78.  A  is  the  boiler;  C  is  the 
head  of  the  still ;  D  the  pipe  leading  to  the  condenser ;  F  the 
spiral  tube  in  which  the  vapor  is  condensed ;  K  the  point  where 
it  is  discharged  into  the  bowl  p ;  R  is  a  discharge  cock,  by  which 
water  is  constantly  supplied  to  the  vessel  I  j  K  L,  so  that  a 


Fig.  79. 


Liebig's  Condensing  Tube. 

current  of  cold  water  is  continually  passing  through  it,  entering 
at  the  bottom  and  issuing  at  the  top.  Sometimes,  in  place  of 
the  still,  a  condensing  tube,  Fig.  79,  is  employed.  The  princi- 
ple is  the  same  as  in  the  still,  but  it  is  more  convenient  for  use 

193.  Describe  the  process  of  distillation.     The  still.     Liebig's  condensing  tube.    The 
alembic. 


106 


THE    ALEMBIC. 


Fig.  80. 


in  the  laboratory  when  it  is  desired  to  distil  email  quantities  of 
liquid,  as  it  can  readily  be  adapted  to  a  flask  of  any  size,  as 
seen  in  the  figure.  It  consists  of  a  tube  of  copper,  b,  through 
which  passes  a  large  glass  tube,  closed  at  both  ends  by  corks, 
by  means  of  which  connections  may  be  formed  at  either  end 
with  smaller  tubes.  Through  the  copper  tube  cold  water  is 
continually  circulating,  entering  by  the  funnel  into  the  lower 
end,  and  flowing  out  above  into  the  bowl.  The  vapor  formed 
in  the  flask  «,  is  condensed  in  &,  and  is  collected,  drop  by  drop, 
in  the  bottle,  c.  Again,  the  same  process  may  be  carried  on  in 
the  Alembic,  of  which  a  representation  is  given  in  Fig.  80.  It 

consists  of  a  glass  boiler,  to 
which  a  head  is  adapted  by 
grinding,  in  such  a  way  that 
the  vapor  which  is  condensed 
upon  its  sides  trickles  into  a 
gutter  and  issues,  drop  by 
drop,  through  the  spout. 
This  is  a  very  convenient 
instrument  for  distillation 
on  a  small  scale. 

194.  Uses  of  Distilla- 
tion. One  of  the  most  im- 
portant uses  of  distillation 
is  the  purification  of  liquids 
fiom  the  foreign  substances 
with  which  they  may  be 
charged.  Thus  muddy  water 
can  be  made  clear  by  boiling 
it  and  condensing  the  vaj  or. 

Alembic.  The  foreign  particles  are  too 

heavy  to  rise  with  the  varor, 

and  remain  in  the  boiler.  Sugar  and  salt  dissolved  in  water 
can  not  rise  in  vapor;  consequently  they  are  L-ft  behind  in  the 
boiler,  while  the  water  is  dislilled  off.  In  such  cases  the  liquid 
left  behind  is  concentrated,  and  this  is  sometimes  one  object  of 
the  process. 

195.  The  separation  of  two  Liquids  by  Distillation.  Two 
liqurds,  thoroughly  mixed,  may  be  separated  by  this  process, 
provided  their  boiling  points  are  different.  Thus,  alcohol  boil- 


194    Explain  the  uses  of  distillation.— 195.  Show  how  two  liquids  may  be  separated 
by  distillation. 


THE    USES    OF    DISTILLATION.  1G7 

ing  at  176°,  while  water  bolls  at  212°,  it  is  quite  evident  that 
the  alcohol  can  be  boiled  and  raised  into  vapor  before  the  water 
is  hot  enough  to  do  the  same ;  and  this  being  condensed,  it  will 
trickle  down  into  the  receiver,  leaving  the  water  behind  it.  To 
ensure  the  success  of  this  process  the  temperature  must  be  kept 
as  near  as  possible  to  the  boiling  point  of  alcohol,  and  below 
that  of  wafer.  O.i  the  same  principle  a  volatile  substance 
m'ght  be  boiled  off,  and  the  liquid  left  behind  made  stronger 
and  purer.  This  last  projess  is  sometimes  called  Condensation. 
The  distillation  of  pure  water  from  salt  water,  which  is  some- 
times done  on  shipboard,  is  accomplished  on  the  same  principles. 
The  salt  and  other  impurities  dissolved  in  the  water  can  not 
rise  with  the  vapor  of  water,  on  account  of  their  greater  spe- 
cific gravity.  The  vapor,  therefore,  produced  by  the  boiling  of 
sea  water,  is  comparatively  pure,  and  when  condensed  in  the 
worm  of  the  still,  proves  a  tolerably  wholesome  water.  These 
processes,  it  can  be  readily  seen  are  matters  of  great  practical 
importance  in  the  arts. 

Experiments  :— Effects  of  Heat:    Vaporization. 

1.  Vaporization.     Heat  the  cause ;  shown  by  heating  water  or  alcohol. 

2.  Solids  are  sometimes  vaporized  without  liquefying ;  shown  by  heating,  in  a  Flor- 
ence flask,  camphor,  sulphur,  benzoic  acid,  sal  ammoniac,  arsenious  acid      Let  a  second 
flask  be  inverted  over  the  tjrst,  that  the  vapors  which  are  formed  may  be  collected  and 
condensed      This  is  called  sublimation. 

3.  Ebullition.     Different  liquids  boil  at  different  temperatures  ;  this  may  be  shown 
by  placing  a  thermometer  in  boiling  water,  ether  and  alcohol.     The  last  two  should  not 
be  boiled  over  a  lamp,  but  by  immersion  in  boiling  hot  water,  in  test  tubes. 

4.  Boil  water  in  a  metallic  vessel  and  in  a  glass  vessel,  successively,  using  the  same 
thermometer  to  show  the  effect  of  nature  of  the  vessel  upon  the  boiling  point. 

6.  Gall  attention  to  toe  fact  that  in  the  boiling  of  water  steam  is  formed  at  the  bottom 
of  the  liquid,  and  not  upon  its  surface 

6.  The  boiling  point  of  liquids  is  elevated  or  depressed  by  the  diminution  or  increase  of 
the  pressure  of  tne  atmosphere.     Water,  ether,  alcohol,  under  tiie  exnausted  receiver  of 
an  air  pump,  boil  respectively  at  70°,  —  44P,  and  3b'°. 

7.  The  principal  fact  connectctt  with  vaporization,  viz.,  the  absorption  and  entire  dis- 
appearance of  a  large  amount  of  heat,  is  shown  by  placing  a  thermometer  in  a  flask  of 
w  iter,  and  heating  over  a  spirit  lamp.     The  temperature  of  the  water  will  rise  until  it 
reaches  212°.     Above  this  point  the  mercury  refuses  to  rise,  though  heat  is  continually 
entering  the  water  at  the  same  rate  as  before. 

8.  The  same  fact  is  shown  by  putting  a  thermometer  into  water  at  90°,  and  placing 
the  whole  under  the  receiver  of  an  air  pump  ;  exhaust,  and  as  soon  as  the  water  begins 
to  boil,  tie  thermometer  sinks,  owing  to  the  absorption  of  heat. 

9.  Again,  if  to  a  pound  of  water  at  212°,  8  pounds  of  red-hot  iron  filings  be  added, 
the  temperature  of  the  water  will  be  found,  on  trial,  not  to  have  been  increased  a  degree. 
Wh  it  has  become  of  the  heat  of  the  red-hot  iron  .' 

13  If  ether,  at  the  ordinary  atmospheric  temperature,  be  subjected  to  diminished 
pressure  by  being  placed  under  the  exhausted  receiver  of  an  air  pump,  it  will  boil  furi- 
ously, and  the  thermometer  will  immediately  sink  very  rapidly,  showing  the  absorption 
ol  a  large  amount  of  heat. 

11.  Place  some  pure  water,  at  62°,  in  a  flask,  over  a  good  spirit  lamp,  and  nofc  the 
number  of  nuauce^  it  takes  to  rise  to  212°,  or  to  gain  150°  of  heat.  Let  it  boil  as  many 
minutes  more,  and  tnen  note  the  temperature  ;  it  svill  be  found  to  be  still  no  higher  than 
212°  ;  yet  it  has  received  actually  150°  of  additional  heat.  What  has  become  of  it? 


1C8  EXPERIMENTS    ON 

12.  Note  the  number  of  minutes  that  it  takes  the  water  in  the  last  experiment  to  boil 
entirely  a\vay :  multiply  by  tae  number  of  degrees  of  heat  imparted  per  minute,  and 
it  wid  be  found  ttiat  1>JOO°  of  heat  have  been  absorbed. 

1  J.  Tne  heat  taus  absorbed  is  giveu  out  again  when  the  vapor  is  condensed.  Let  a 
tall  j:ir  be  filled  with  11  cubic  iucaes  of  water  at  81° ;  condense  steam  at  212°  into  it 
until  2  cubic  inches  have  been  added  to  the  11,  and  it  will  be  found  taat  t'.ie  temperature 
of  tae  water  has  increased  to  212"* ;  i  e..  the  heat  contained  in  steam  at  212°  is  sufficient, 
waea  condensed,  to  heat  5i  times  as  much  water  as  that  from  which  it  was  produced, 
from  32°  to  212° ;  i.  e  ,  18lA  180°X»2L  ^°-  See  F.g.  55. 

14.  The  boiling  point  varies  with  variation  in  pressure  ;  this  may  be  shown  by  boiling 
water  in  a  flask,  tightly  corked,  having  a  thermometer  in  it.  The  steam  being  prevented 
escaping,  reacts  upon  the  water  and  soon  exerts  a  powerful  pressure,  and  the  thermome- 
ter at  once  commences  to  rise.  Remove  the  pressure,  by  allowing  the  ste;un  to  escape, 
a»d  the  temperature  falls.  This  may  be  shown  by  Marcet's  apparatus,  or  the  steam 
flask.  Shut  the  stop  cock  of  each,  when  the  water  commences  boiang  and  the  thermome- 
ter will  rise  above  212° ;  open  it  again,  and  it  will  immediately  fall  to  212°  ;  exhaust  the 
air  from  the  steam  flask,  by  tae  air  pump,  and  it  will  boil  at  a  temperature  lower  than 

1  3.  The  Culinary  Paradox.  Boil  water  in  a  flask,  close  it  quickly  by  a  cork  ;  remove 
it  frain  the  lamp,  invert  it,  and  apply  cold  water  to  tae  upper  part ;  the  boiling  will  re- 
commence with  violence ;  apply  hot  water  and  it  will  cease. 

1  .<.  Wollaston's  steun  bulb  and  jar  of  cold  water,  shows  the  moving  forces  in  the 
steam  engine.     Boil  the  water  in  steam  bulb  until  the  piston  has  reached  the  top  of  the 
cylinder  ;  then  dip  in  cold  water,  and  the  piston  will  descend. 

17.  That  water  expands  1700  times  in  vaporizing,  may  be  shown  by  a  cylinder  in 
which  there  is  a  cubic  inch  of  water,  fitted  with  a  pis  on.  The  water  is  boiled  away  and 
the  piston  is  forced  up  until  the  capacity  of  the  space  below  it  amounts  to  1700  cubic 
inches 

1.  Spheroidal  S  'ate.    Heat  a  copper  ball  red-hot  in  a  powerful  lamp,  and  dip  it 
quickly  into  water  at  temperature  of  96°,  in  a  glass  jar.     It  will  remain  red-hot  for  a 
considerable  leng  h  of  time. 

2.  Drop  water  into  a  red-hot  capsule  of  copper,  until  it  is  nearly  full ;  then  remove 
the  lamp.     The  water  will  not  boil  until  the  lamp  is  taken  asvay. 

3.  Drop  water  into  a  red-hot  flask  of  copper  and  cork  it  tightly  ;  remove  the  lamp  ; 
the  cork,  in  a  few  ir.oaients,  will  be  driven  out  with  great  violence. 

4.  Heat  a  copper  dish,  pierced  with  holes,  red-hot,  and  drop  a  little  water  upon  it 
gently  from  a  glass  dropping  tube;  tue  water  will  not  run  thiough ;  remove  the  lamp 
and  the  water  will  then  readily  flow. 

5.  Drop  liquefied  sulphurous  acid  into  a  red-hot  capsule  of  platinum,  and  test  the 
temperature  with  a  thermoaieter. 

6.  Drop  water  into  a  red-hot  platinum  capsule  until  it  is  quite  full,  and  then  insert  a 
delicate  thermometer;  the  mercury  will  only  rise  to  'A)6°  F. 

7.  Throw  a  mixture  of  solidified  carbonic  acid  and  erher  into  a  red-hot  platinum  cap- 
sule; the  ether  will  almost  immediately  catch  fire,  producing  a  powerful  blaze:  intro- 
duce a  thermometer  into  the  mixture  beneath  the  flame,  and  the  mercury  will  be  fro/en. 
This  is  owing  to  the  low  temperature  at  which  the  carbonic  ucid  is  turotra  into  tue  sphe- 
roidal state. 

8.  Introduce  into  the  same  mixture  a  small  platinum  spoon  fil'ed  with  mercury;  it 
will  be  frozen,  and  may  be  turned  out  upon  the  table  in  the  i-o,id  Ftate. 

9.  Introduce  a  little  water  in  the  same  manner  into  the  same  mixture,  and  it  also  will 
be  frozen,  and  may  be  turned  out  upon  the  table  as  ice 

10.  Throw  a  few  grains  of  iodine  into  a  red-hot  platinum  crucible,  over  a  lamp,  and 
it  will  vaporize  slowly  in  consequence  of  being  thrown  into  the  spheioidal  state  at  a  low 
temperature,  and  only  a  little  heat  reaching  it ;  remove  the  lamp,  and  it  will  at  once 
burst  into  a  splendid  vio'et  cloud. 

1 1.  For  these  experiments  there  is  needed  a  powerful  alcohol  vapor  lamp,  and  thick 
capsules  of  copper,  piatinum,  or  silver,  which  retain  he-it  for  some  time. 

1.  Distillation.  Fill  a  common  retort,  half  full  of  water,  and  boil  it  slowly  over  a 
spirit  lamp ;  the  vapor  will  condense  in  the  neck  of  the  retort  and  trickle  drop  by  drop 
from  its  beak  into  a  cup  placed  to  receive  it. 

2  Take  some  well  water  and  pour  into  it  a  few  drops  of  sol.  of  oxalic  acid  ;  a  white 
cloud  will  be  produced,  showing  the  presence  of  lime  in  the  water.     Pour  the  same  water 
into  a  retort  nnd  distill  as  before:  collect  the  distilled  water  and  test  for  lime  again;  no 
lime  will  be  found,  showing  that  the  water  has  been  purified  by  distillation. 

3.  Dilute  alcohol  with  water  until  it  will  no  longer  inflame  when  a  taper  is  put  into  it ; 
then  pour  the  mixture  into  an  alembic,  h-iving  a  thermometer  in  it ;  heat  to  180°.  not 
higher;  vapor  will  rise  and  condense  in  the  neck,  and  finally  fall,  drop  by  drop,  into  a 
wine  glass  placed  to  catch  it ;  apply  the  taper  and  it  will  burn,  showing  that  the  alcohol 


EVAPORATION.  1G9 

his  been  separated  from  the  water.     This  will  show  how  alcohol  is  separated  from  watery 
solutions. 

4.  Try  the  same  experiment  with  wine. 

5.  Ditto  with  brandy  diluted  with  water;  with  other  liquors. 

6.  Boil  inuddy  or  turbid  water  in  a  retort,  aiid  observe  the  clearness  of  the  residual 
water. 


§  V.    Effects  of  Heat :— Evaporation ; 

196.  Evaporation.    Evaporation  has  been  described  as  the 
second  mode  of  vaporization.     It  differs  from  ebullition,  in  tak- 
ing place  from  the  surface  of  liquids,  while  ebullition  consists  in 
the  formation  of  vapor  at  the  bottom  of  a  liquid,  immediately 
in  contact  with  the  surface  of  the  boiling  vessel,  and  accompa- 
nied by  more  or  less  commotion  in  the  fluid  as  the  vapor  rises 
through  it.      Evaporation  is  a  slow  and  quiet  process,  unattended 
by  violent  action  ;  ebullition  is  rapid,  and  must  be  kept  up  by 
artificial  mean^.      Evaporation  goes  on  at  common  temperatures, 
and  may  take  place  even  at  the  lowest,  and  during  the  coldest 
seasons ;  while  ebullition  requires  a  high  degree  of  heat,  or  at 
least  the  removal  of  atmospheric  pressure. 

197.  Evaporation   takes  place  at  common  temperatures; 
Hsat  its  cause.   'To  prove  that  evaporation  takes  place  at  natu- 
ral temperatures,  nothing  more  is  necessary  than  to  expose  a 
quantity  of  water  to  the  open  air,  in  a  shallow  vessel ;  the  liquid 
will  be  found  gradually  to  diminish,  and  will  finally  disappear 
entirely.     If  a  quantity  of  water,  or  ether,  be  carefully  weighed, 
at  the  end  of  an  hour  it  will  be  found  to  have  lost  weight  very 
perceptibly.     It  was  for  a  long  time  thought  that  the  air  was 
th'3  cause  of  evaporation,  and  that,  in  consequence  of  its  affinity 
for  different  liquids,  it  dissolved    them  with  varying  degrees 
of  rapidity,  as  water  dissolves  the  different  salts ;  but  it  is  im- 
possible to  attribute  the  effect  to  this  cause,  for  it  is  an  estab- 
lishe  1  fast  that  evaporation  takes  place  in  vacuo,  that  the  air 
positively  retards  the  process,  and  that  one  of  the  best  means 
of  accelerating  it  is  to  remove  the  air  altogether.      The  sole  cause 
of  evaporation  is  Heat.     "We  know  that  this  is  true  in  the  ca?e 
of  ebullition,  because  we  perceive  the  actual  application  of  the 
heat ;  but  in  the  case  of  evaporation  it  is  not  so  apparent,  be- 

193.  What  is  the  second  mode  of  vaporization  ?  In  what  respects  does  evaporation 
differ  from  ebullition  ? — 197.  Prove  that  evaporation  takes  place  at  common  temperatures. 
Show  that  it  is  produced  by  heat,  and  not  by  the  action  of  the  air. 


170  HEAT    ITS    CAUSE. 

cause  there  is  no  actual  application  of  heat,  and  the  amount 
required  is  gathered  up  silently  and  quietly  on  every  hand.  It 
would  appear  that  in  the  liquid  state  the  particles  of  matter 
having  already  begun  to  separate  from  each  other  and  acquire 
facility  of  motion,  are  readily  pushed  still  further  apart  by  the 
heat  which  liquids,  at  ordinary  temperatures,  collect,  that  they 
at  length  cease  to  oppose  any  barrier  to  the  passage  of  light, 
become  invisible,  and  lighter  than  air,  and  finally  rise  and 
escape.  The  experiments  of  Dr.  Dalton  not  only  prove  that 
heat  is  the  true  cause  of  the  formation  of  vapor,  but  also  that 
the  actual  quantity  which  can  exist  in  any  given  space  is  de- 
pendent solely  upon  temperature.  If  a  little  water  be  placed  in 
a  dry  glass  flask,  a  quantity  of  vapor  will  be  formed  proportion- 
ate to  the  temperature ;  at  32°  the  flask  will  contain  but  a  very 
small  quantity  of  vapor ;  at  40°  more  vapor  will  exist  in  it ;  at 
50°  it  will  contain  still  more ;  and  at  60°  the  quantity  will  be 
still  further  increased.  If,  then,  under  these  circumstances,  the 
temperature  of  the  flask  be  again  suddenly  reduced  to  40°  a 
certain  portion  of  the  vapor  will  be  reconverted  into  water ;  the 
quantity  which  retains  the  form  of  vapor  remaining  precisely 
the  same  as  when  the  temperature  was  originally  at  40°. 

198.  The  amount  of  Vapor  formed,  and  its  elasticity,  are 
proportionate  to  the  temperature.  Vapors,  like  gases,  possess 
a  certain  elastic  force ;  by  this  is  meant  that  they  possess  a 
tendency  to  expand  indefinitely,  and  are  only  prevented  from 
doing  so  by  the  pressure  of  counteracting  forces,  of  which  the 
most  important  is  the  pressure  of  the  atmosphere.  If  confined 
in  a  closed  vessel  a  vapor  exerts  a  certain  pressure  upon  the 
sides  of  the  vessel,  in  consequence  of  its  elasticity  or  tendency 
to  expand,  and  the  degree  of  this  pressure,  and  the  amount  of 
vapor  formed,  will  depend  upon  the  temperature  to  which  the 
vessel  is  subjected.  If  the  vessel  be  a  bottle,  tightly  closed,  and 
containing  a  small  amount  of  water,  while  the  remainder  of  the 
space  is  filled  with  air,  the  air  within  the  bottle  will  not  prevent 
the  liquid  from  evaporating ;  a  certain  amount  will  pass  into  the 
state  of  vapor,' depending  upon  the  temperature  ;  its  elastic  force 
will  be  added  to  the  elastic  force  of  the  air  confined  in  the  bot- 
tle, and  a  pressure  exerted  upon  the  inside,  tending  to  burst  it. 
If,  under  these  circumstances,  the  stopple  of  the  bottle  be  re- 
moved, a  portion  of  the  mixed  air  and  vapor  will  rush  out :  if 

198.  Prove  that  vapors,  like  gases,  possess  elasticity,  and  exert  pressure  upon  the  in- 
side of  a  vess-el  containing  them.  What  effect  has  increase  of  temperature  upon  the 
elastic  force  of  vapors  ?  What  degree  cf  force  may  be  exerted  by  this  means  ? 


THZ  AMOUNT  OF  VAPOR  AND  ITS 


171 


Fig.  81. 


the  vessel  employed  be  a  bell  glass,  closed  at  (he  top,  and  open 
at  the  bottom,  having  a  small  quantity  of  water  in  it,  and  placed 
in  a  bath  of  mercury,  the  mercury  will  be  depressed  as  the  vapor 
is  formed,  showing  that  the  elastic  force  of  the  gaseous  contents 
of  the  bell  glass  has  been  increased.  If  the  temperature  bo 
steadily  raised  the  amount  of  vapor  formed,  and  the  elastic 
power  of  the  mixed  air  and  watery  vapor,  will  increase  at  an 
equal  rate,  and  the  pressure  upon  the  sides  of  the  vessel  will  be 
correspondingly  augmented.  When  212°  is  reached  the  water 
will  begin  to  boil,  and  the  pressure  be  still  further  augmented ; 
as  the  temperature  rises  beyond  this  point  the  pressure  will  go 
on,  increasing  in  force,  and  eventually  attain  such  a  degree  that 
no  amount  of  external  pressure  can  resist  it,  and  the  vessel  will 
be  rent  in  twain.  The  tendency,  therefore,  for  a  liquid  to  pass 
into  vapor,  is  not  only  due  to  heat,  but  is 
heightened  as  the  temperature  increases, 
and  when  a  certain  degree  has  been  at- 
tained, becomes  irresistible. 

199.  These  truths  illustrated  by  ex- 
periment. Let  D  c  A  be  a  glass  tube, 
curved  like  a  siphon,  the  upper  extremity 
open  to  the  air,  the  other  closed ;  let  the 
tube  be  half  filled  with  mercury,  so  that 
it  will  enclose  about  an  inch  of  air  in 
the  short  L>g,  and  a  drop  of  liquid  ether  be 
introduced  in  such  a  way  as  to  rise  through 
the  mercury,  and  enter  the  space  filled  with 
air ;  this  may  be  readily  done  by  a  skillful 
manipulation  of  the  apparatus.  As  soon  as 
the  liquid  reaches  the  confined  air  the  mer- 
cury in  the  short  leg  will  be  depressed  below 
its  former  level ;  this  depression  is  due  to 
the  elastic  force  of  the  vapor  of  ether 
formed.  If  the  tube  be  dipped  into  warm 
water,  at  temperature  of  100°  Fig.  81,  the 
column  of  mercury  will  be  still  further  de- 
pressed, and  the  more  as  the  temperature 
The  amount  and  elasticity  rises;  if,  on  the  contrary,  the  temperature 
0fVaTemp7raturTdt0  l;e  diminished,  the  column  of  mercury  in 
the  short  log  will  rise,  showing  that  the 
elastic  force  is  diminished.  From  this  experiment,  it  is  clear 


199.  Prove  this  fact  by  experiment.     Describe  F;g.  81. 


172        ELASTICITY    PROPORTIONATE    TO    TEMPERATURE. 

that  the  liquid  ether  introduced  into  confined  air  is  not  prevented 
from  passing  into  vapor  by  the  pressure  of  the  confined  air,  nor 
by  the  pressure  of  the  excess  of  the  column  of  mercury  in  the 
long  leg  over  that  in  the  short  leg,  nor  by  the  atmospheric  press- 
ure which  is  operating  upon  the  mercury  through  the  open  end 
of  the  tube,  but  that  it  proceeds  in  spite  of  these  opposing  forces, 
and  even  acts  against  the  whole  pressure  of  the  atmosphere  at  D. 
It  further  appears  that  this  elastic  force  is  increased  by  heat,  and 
is  diminished  by  cold.  If,  instead  of  leaving  a  space  filled  with 
air  in  the  short  leg  of  the  tube,  it  be  entirely  filled  with  mer- 
cury, and  a  drop  of  liquid  ether  introduced,  the  same  effect  will 
result;  the  mercury  will  be  immediately  depressed  in  the  short 
leg,  and  the  more,  the  higher  the  temperature  employed ;  it  will 
also  be  seen  that  the  vapor  formed  is  an  elastic,  transparent,  and 
invisible  fluid,  like  the  air. 

200.  The  rapidity  of  evaporation  varies  with  the  press- 
ure to  be  overcome;  in  a  Vacuum,  it  is  instantaneous.  In  the 
preceding  experiment  the  evaporation  of  the  liquid  goes  on  very 
slowly  and  gradually,  on  account  of  the  pressure  of  the  mercury 
and  of  the  atmosphere,  which  must  first  be  overcome ;  if  this 
pressure  be  diminished  it  will  proceed  more  rapidly ;  if  it  be 
entirely  removed,  the  evaporation  will  be  instantaneous.  In  a 
vacuum,  this  counteracting  pressure  is  entirely  removed,  and 
consequently,  if  a  small  portion  of  any  vaporizable  liquid  be 
introduced,  its  vapor  will  immediately  fill  the  whole  of  the  va- 
cant space.  The  quantity  and  elasticity  of  the  vapor  will  depend 
upon  the  temperature,  and  they  will  both  be  precisely  the  same 
as  though  the  evaporation  had  taken  place  in  air  at  the  same 
temperature,  instead  of  a  vacuum ;  the  only  difference  in  the 
two  cases  will  be  that,  in  a  vacuum,  the  evaporation  takes  place 
instantaneously,  while  in  the  air,  time  is  required  for  its  diffu- 
sion, owing  to  the  pressure  which  the  air  exerts ;  and  in  the 
vacuum,  the  elasticity  of  the  vapor  is  the  only  force  tending  to  de- 
press the  mercury,  while  in  air,  the  elasticity  of  the  vapor  added 
to  that  of  the  air,  is  the  depressing  force,  and  consequently  pro- 
duces a  greater  effect.  This  may  readily  be  proved  by  the  fol- 
lowing experiment.  Let  A,  Fig.  82,  be  a  glass  tube,  about  36 
inches  in  length,  open  at  the  lower  end,  and  let  it  be  completely 
filled  with  mercury,  closed  with  the  finger,  and  inverted,  in  a  vessel 
also  of  mercury.  As  soon  as  the  finger  is  withdrawn,  the  mercury 


200.  What  effect  has  pressure  upon  the  rapidity  of  evaporation?    How  does  evapora- 
tion proceed  in  a  vacuum  ? 


THE    RAPIDITY    OF  EVAPORATION 


173 


will  at  once  sink  in  the  tube  till 
the  height  of  the  top  of  the  col- 
umn above  the  level  of  the  mer- 
cury in  the  lower  vessel  is  about 
30  inches.  The  reason  of  this  is, 
that  the  weight  of  a  column  of 
mercury  of  this  height  is  exactly 
equal  to  the  weight  of  a  column 
of  air  of  an  equal  base,  extending 
to  the  extreme  limits  of  the  at- 
mosphere, and  the  column  of 
mercury,  and  that  of  air,  exactly 
balance  each  other.  All  the  space 
in  the  interior  of  the  tube,  above 
30  inches,  is  entirely  free  from 
air,  and  a  perfect  vacuum,  some- 
times called  the  torricellian  vacu- 
um, after  Torricelli,  a  celebrated 
Italian  philosopher.  If  now,  a 
drop  of  ether  be  introduced  into 
the  open  end  of  the  tube,  be- 
neath the  mercury,  it  will  rapidly 
rise,  in  consequence  of  its  supe- 
rior lightness,  until  it  reaches 
the  vacant  space ;  a  portion  of  it  will  then  immediately  flash  into 
vapor,  and  the  elasticity  of  the  vapor  formed  will  at  once  depress 
the  mercury  considerably  below  the  point  at  which  it  stood  a 
moment  before,  as  is  seen  in  the  tubes  B,  D,  &  E.  The  quantity 
and  elasticity  of  the  vapor  will  in  all  cases  be  exactly  propor- 
tional to  the  temperature,  and  the  mercury  will  continue  to  sink 
until  as  much  of  the  liquid  ether  has  evaporated  as  the  tem- 
perature is  capable  of  sustaining  in  the  vaporous  state.  The 
vacuum  will  then  be  saturated  with  vapor,  i.  e.,  it  will  hold  as 
much  vapor  as  is  capable  of  existing  in  it  at  that  particular  tem- 
perature. If  the  temperature  be  elevated  above  this  point, 
more  ether  will  be  evaporated,  and  the  mercury  still  further 
depressed ;  if  the  temperature  be  lowered,  some  of  the  vapor 
will  be  condensed  into  the  liquid  state  again,  and  the  mercury 
will  rise. 

201.    The    amount  of  evaporation  of  different    liquids  in 
a  vacuum,  at  the  same  temperature,  is  unequal.     Let  the  four 


The  rate  of  evaporation  of  different 
Liquids  unequal. 


Describe  the  experiment  by  which  this  is  proved. — 201.  Show  that  the  rapidity  of 
evaporation  of  different  liquids  in  a  vacuum  is  unequal. 


174 


VARIES    WITH    PRESSURE. 


Fig.  83. 


tubes,  A,  B,  D,  E,  Fig.  82,  be  all  filled  with 
mercury,  in  the  manner  already  described, 
and  let  the  mercury  in  each  have  sunk  to 
30  inches,  leaving  a  vacuum  above  it  in  eacl 
tube  ;  let  the  tube  A  be  preserved,  unchanged, 
as  a  standard  for  the  others,  and  into  the 
tubes  B,  D,  and  E,  let  some  drops  of  water, 
alcohol  and  ether,  be  respectively  introduced. 
As  soon  as  they  reach  the  vacuum  in  the  up- 
per part  of  each  tube,  the  mercurial  column 
in  each  case  will  be  depressed,  but  not  to 
the  same  extent  in  all.  In  the  tube  D,  con- 
taining the  alcohol,  it  will  be  more  depressed 
than  in  the  tube  B,  and  in  the  tube  E,  much 
more  depressed  than  in  either  B,  or  D.  This 
shows  that,  at  the  same  temperature,  the 
vapors  of  different  liquids  do  not  possess  the 
same  elastic  force ;  at  68°  the  elastic  force 
of  the  vapor  of  ether  is  nearly  25  times 
greater  than  that  of  the  vapor  of  water. 

202.  The  elastic  force  of  the  vapor  in 
a  saturated  space  does  not  vary  with  the 
pressure  to  which  it  is  subjected ;  but  it  does 
vary  with  the  temperature.  Let  Fig.  83 
represent  a  barometer  tube,  completely  filled 
with  mercury,  dipping  into  a  deep  cistern  of 
iron,  c  also  filled  with  the  same  fluid.  On 
introducing  a  few  drops  of  ether  beneath  the 
lower  edge  of  the  tube,  it  will  rise  to  the 
upper  part,  and  will  there  evaporate.  By 
this  formation  of  vapor,  the  mercurial  col- 
umn will  be  depressed,  and  at  the  same  time 
a  small  portion  of  liquid  ether  will  float  upon 
its  upper  surface,  at  s.  The  elastic  force  of 
this  enclosed  vapor  is  measured  by  the  dis- 
tance to  which  it  depresses  the  mercurial 
column.  If  its  elasticity  be  increased,  the 
column  of  mercury  is  lowered ;  if  it  be  di- 
minished, the  mercurial  column  rises ;  if  it 
remains  unchanged,  the  height  of  the  mercu- 
rial column  above  the  level  of  the  mercury 
in  the  vessel  be^w,  remains  unchanged. 
Now,  if  the  barometer  tube  be  depressed  by 
the  hand  in  the  lower  vessel,  this  will  tend 


THE    ELASTICITY 


175 


to  drive  the  mercury  farther  up  the  tube,  and  compress  the 
vapor ;  if,  on  the  contrary,  the  tube  be  raised  out  of  the  vessel, 
the  mercury  will  tend  to  fall,  and  the  pressure 
Fi<*  84  on  ^ie  vaPor  wiH  be  diminished.     In  either 

case,  no  effect  whatever  is  produced  in  the 
height,  s,  of  the  mercurial  column,  #,  above 
the  level,  c,  ^,  of  the  mercury  in  the  vessel 
below.  The  elastic  force  of  the  vapor,  there- 
fore, whether  it  be  compressed,  or  expanded, 
remains  the  same.  When  compression  takes 
place,  in  consequence  of  driving  the  tube 
down,  a  portion  of  the  vapor  is  condensed  into 
the  liquid  state  again,  and  the  elastic  force  of 
the  vapor  which  remains,  continues  the  same 
a^  before.  When  the  pressure  is  diminished 
by  drawing  the  tube  up,  an  additional  amount 
of  the  ether  evaporates,  which,  adding  its 
elasticity  to  that  of  the  original  vapor,  pre- 
serves its  elastic  force,  unchanged.  The 
height  of  the  column  of  mercury  remains, 
therefore,  the  same,  whether  the  tube  be  ele- 
vated, or  depressed ;  but  the  amount  of  liquid, 
ether  above  the  mercury  varies  considerably. 
As  the  tube  is  lowered,  the  mercury  rises,  and 
the  space  occupied  by  the  vapor  contracts  at 
the  same  rate,  while  the  amount  of  liquid 
ether  increases ;  as  the  tube  is  elevated,  the 
mercury  sinks,  and  the  space  occupied  by  the 
vapor  increases  at  the  same  rate,  while  the 
amount  of  liquid  ether  is  diminished, 

It  is  far  otherwise  when   the  temperature 
is  made  to  vary,     Let  a  similar  barometer 
tube  have  placed  over  it  another  tube,  con- 
,    siderably  larger  than  itself,  and  closed  at  the 

E  •astir.ity  varies  with.     ,  rr-       r>  j  T  ^ 

Temperature.  bottom,  -C  tff-  84,  and  Jet  Jiot  water  be  poured 
into  this  tube,  the  increased  temperature  causes  an  additional 
poraon  of  ether  to  evaporate  in  the  barometer  tube,  and  a  cor- 

202.  Does  the  elastic  force  of  a  vapor  vary  with  the  pressure  to  which  it  is  subjected, 
or  '.\itii  its  temperature?  Prove  this  by  experiment.  Explain  the  increase  in  the  vol- 
ume of  liquid  ether  by  increasing  the  pressure.  Explain  the  diminution  in  its  volume 
bv  the  removal  of  pressure.  Why,  in  both  cases,  does  tho  height  of  the  column  of  mer- 
cury renuan  ihe  same?  What  is  the  effect  of  applying  hot  water  to  a  portion  of  the 
tube  only  ?  Why  can  not  the  elastic  force  of  vapor  rise  above  that  due  to  the  tempera- 
ture 01  the  coldest  part  of  the  vessel? 


176  VARIES    WITH   TEMPERATURE. 

responding  increase  in  the  elasticity  of  the  original  vapor,  by 
which  the  column  of  mercury  is  rapidly  depressed.  As  water 
of  higher  temperature  is  employed,  the  effect  is  increased,  and 
iinally,  when  the  boiling  point  of  the  ether  is  reached,  the  elas- 
ticity of  the  vapor  is  great  enough  to  drive  the  mercury  entirely 
out  of  the  tube ;  or,  in  other  words,  its  elastic  force  is  exactly 
equal  to  that  of  the  surrounding  air ;  if  a  higher  temperature 
than  the  boiling  point  be  employed,  its  elasticity  becomes  great- 
er than  that  of  the  surrounding  air,  and  can  be  made  to  sus- 
tain a  column  of  mercury  varying  in  height  with  the  tempera- 
ture employed.  On  the  contrary,  if  this  process  be  reversed, 
and  the  temperature  surrounding  the  barometer  tube  be  dimin- 
ished, the  elastic  force  of  the  vapor  will  be  diminished,  and  the 
mercurial  column  will  rapidly  rise  until  it  has  attained  the 
height  of  30  inches.  The  above  statements,  however,  only 
hold  good  so  long  as  the  tube  is  heated  uniformly  through  its 
whole  extent;  if  only  a  portion  of  the  tube  be  heated,  a  very  dif- 
ferent result  takes  place ;  the  additional  vapor  formed  in  the 
hot  portions  of  the  tube  is  condensed  again  in  those  which  are 
not  thus  heated,  and  consequently  there  is  no  steady  and  pro- 
gressive increase  of  the  elastic  force ;  this  force  can  never  ex- 
ceed that  which  the  vapor  formed  in  the  coolest  part  naturally 
possesses,  because  the  excess  of  vapor  is  at  once  condensed 
as  soon  as  it  reaches  this  colder  space.  In  other  words,  its 
e^a^tic  force  can  never  rise  above  that  due  to  the  lowest  temper- 
ature which.prevails  anywhere  within  the  tube;  thus  if,  instead 
of  applying  hot  water  along  the  whole  length  of  the  tube,  in  the 
last  experiment,  the  hand  be  simply  applied  at  the  upper  part 
of  the  tube,  the  ether  may  be  made  to  boil,  but  the  height  of 
the  co!umn  of  mercury  is  but  little  affected,  for  the  additional 
ether  vapor  produced  is  at  once  condensed,  and  its  elastic  force 
destroyed  in  those  parts  of  the  tube  which  remain  unheated. 
From  what  has  been  said  it  is  evident  that,  in  order  to  increase 
the  elastic  force  of  vapor,  it  is  necessary  to  confine  or  compress 
if,  and  at  the  same  time  raise  its  temperature.  If  it  be  com- 
pressed only,  the  effect  is  merely  to  condense  a  portion  of  it 
into  water,  leaving  its  elastic  force  unchanged ;  if  it  be  heated, 
simply,  without  being  compressed  or  confined,  it  expands  indefi- 
nitely, and  its  ela-tic  force  also  remains  unchanged.  These 
facts  are  of  fundamental  importance  in  the  steam  engine.  To 
obtain  mechanical  power  from  steam,  it  must  be  both  compressed 
and  heated,  and  this  is  the  reason  why  a  very  strong  boiler, 
and  a  very  hot  fire,  are  necessary  to  develop  the  mechanical 


THE  ELASTIC  FORCROF  VAPOR  IN  TWO  CONNECTING    177 

power  of  steam  from  the  inert  state  in  which  it  exists  at  the 
tima  of  its  first  formation. 

Table  of  the  elastic  force  of  the  vapor  of  Water  at  different  temperatures: 


Pressure. 

Volume  of  Vapor 

Temperature. 

compared  with  that 
of  the  Water 

Inches  of  Mercury 

Pounds  per 

sustained. 

square  inch. 

producing  ic  as  1. 

—40 

0.052 

0.0255 

650588 

140 

0.104 

0.05 

342984 

32° 

0.199 

0.10 

182323 

50° 

0.373 

0.18 

102670 

100.°4 

1.873 

0.92 

22513 

150.°8 

7.530 

3.69 

6114 

201.  °2 

24.062 

11.80 

2u75 

212.° 

29.921 

14.67  or  15 

1696 

The  elastic  force  of  all  vapors,  if  compared  at  temperatures 
equally  distant  from  their  boiling  points,  whether  above  or  below 
them,  is  very  nearly  equal.  Thus  water,  at  242°,  i.  e.,  30° 
above  212°,  its  boiling  point,  has  an  elastic  force  of  52.90  inches 
of  mercury.  Ether,  at  134°,  30°  above  104°,  its  boiling  point, 
has  an  elastic  force  of  50.9  inches.  Water,  at  182°,  30°  below 
212°,  has  an  elastic  force  of  16  inches.  Ether,  at  74°,  30° 
below  its  boiling  point,  104°,  has  an  elastic  force  of  16.10  inches, 
i.  e.,  the  elasticity  of  these  two  vapors,  at  the  above  tempera- 
tures, is  very  nearly  equal. 

203.  The  elastic  force  of  vapor  in  two  connecting-  vessels 
of  different  temperature  can  not  rise  above  the  elastic  force 
of  the  colder  vessel.  When  two  vessels,  containing  the  same 
liquid,  at  different  temperatures  are  connected  by  a  tube  com- 
manded by  a  stop-cock,  so  long  as  the  stop-cock  is  closed,  the 
elasticity  of  the  vapor  in  the  hotter  vessel  is  proportionably 
greater  than  that  of  the  vapor  in  the  colder.  If  the  stop-cock 
be  opened,  and  a  communication  established  between  them,  the 
elasticity  of  ths  whole  apparatus  will  jiot  be  the  mean  of  that 
which  existed  in  the  two  vessels  previously,  but  that  which  cor- 
responds to  the  temperature  of  the  colder.  Let  the  vessel  A, 
in  Fig.  85,  containing  water  at  the  temperature  of  32°,  be 
placed  in  a  vessel  of  pounded  ice,  and  let  the  vessel  B  contain 
water  at  the  temperature  of  212°.  As  long  as  the  vessels  do 
not  communicate,  the  pressure  in  the  vessel  A  will  be  measured 


203.  What  is  the  elastic  force  of  vapor  contained  in  two  connecting  vessels  which  are 
unequally  heated  ?    Prove  this  fact  by  experiment. 
8* 


178  VESSELS  IS   THAT    OF    THE    COLDER. 

Fig    85. 


The  elastic  force  of  vapor  in  two  connecting  vessels  of  different  temperature 
can  not  nse  above  the  elastic  force  of  the  colder  vessel. 

by  a  column  of  mercury  0.199  inches  in  height;  in  the  vessel 
B,  by  a  column  29.921  inches  in  height.  But  as  soon  as  the 
communication  is  established,  by  opening  the  stop-cock  c,  the 
vapor  in  B,  in  consequence  of  its  high  pressure,  rushes  over  into 
the  vessel  A,  where  it  is  immediately  condensed,  thereby  di- 
minishing the  pressure  in  B,  and  continues  to  do  so  until  the 
pressure  in  B  is  brought  down  to  the  same  point  as  the  pressure 
in  A.  In  such  ca-es  the  pressure  becomes  equal  in  the  two  ves- 
sels, and  can  not  rise  above  that  which  is  proper  to  the  lowest 
of  the  two  temperatures.  This  is  a  principle  of  the  greatest 
importance  in  the  operation  of  the  steam  engine,  and  shows 
how  it  is  that  when  the  communication  is  opened  between  the 
condenser  and  the  end  of  the  cylinder  towards  which  the  piston 
is  moving,  the  pres-ure,  or  tension  of  the  steam  in  that  end  of 
the  cylinder  is  brought  down  at  once  to  the  degree  corresponding 
to  the  temperature  of  the  condenser,  and  this  without  at  all  di- 
minishing the  temperature  of  the  cylinder.  If  the  temperature 
of  the  condenser  be  kept  at  32°,  the  steam  from  the  cylinder  is 
condensed  into  water  as  fast  as  it  enters,  and  the  elastic  force  of 
the  vapor  eventua'ly  left  in  the  cylinder  is  reduced  to  the  tension 

What  connection  has  this  fact  with  the  escape  of  steam  from  the  cylinders  of  the  steam 
engine  into  the  condenser?  In  what  did  the  improvement  of  Watt,  in  the  steam  engine, 
eonsist?  Show  how  a  yacuum  may  be  produced  in  the  cylinder.  What  suggested 
the  idea  to  Mr.  Watt? 


EVAPORATION    OF    LIQUIDS    IN    AIR   DIFFERENT.          179 

due  to  the  temperature  of  32°,  i.  e.,  0.199  in.  This  tension  is  so 
small  that  a  nearly  perfect  vacuum  is  thus  produced  throughout 
both  the  cylinder  and  the  condenser.  This  was  the  capital  im- 
provement made  in  the  steam  engine  by  Mr.  Watt.  Being 
asked,  in  1817,  whether  he  recollected  how  the  first  idea  of  his 
great  discovery  came  into  his  mind,  he  replied,  "  Oh  yes,  per- 
fectly ;  one  Sunday  afternoon  I  had  gone  to  take  a  walk  on  the 
green  of  Glasgow,  and  when  about  half  way  between  the  Herd's 
house  and  Arn's  well,  my  thoughts  having  been  naturally  turned 
to  the  experiments  I  hud  been  engaged  in  for  saving  heat  in  the 
cylinder,  at  that  part  of  the  road  the  idea  occurred  to  me  that, 
as  steam  was  an  elastic  vapor,  it  would  expand  and  rush  into  a 
previously  exhausted  space ;  and  that  if  I  were  to  produce  a 
vacuum  in  a  separate  vessel,  and  open  a  communication  between 
the  steam  in  the  cylinder  and  the  exhausted  vessel,  such  would 
be  the  consequence." 

204.  The  rate  of  the  evaporation  of  different  Liquids  in  the 
air  is  different.  It  has  been  shown  that  the  rate  of  evaporation 
of  different  liquids  in  the  torricellian  vacuum  is  different.  The 
same  is  also  true  of  their  evaporation  in  air.  If  the  tubes  in 
the  apparatus  before  described,  Fig.  82,  be  half  filled  with  mer- 
cury, and  then  inverted  in  a  vessel  of  the  same  liquid,  the  upper 
part  of  each  tube  will  be  filled  with  air ;  now  let  a  few  drops 
of  water,  alcohol  and  ether,  be  introduced  into  the  three  tubes 
respectively,  and  it  will  be  found  that  almost  immediately  the 
mercury  will  be  unequally  depressed  in  each  tube.  The  great- 
est depression  will  take  place  in  the  tube  into  which  the  ether 
has  been  introduced,  and  the  least  in  the  one  into  which  the 
water,  while  the  tube  containing  the  alcohol  will  exhibit  a 
depression  intermediate  between  the  two.  This  shows  conclu- 
sively that  different  liquids  evaporate  in  air  with  different  de- 
grees of  rapidity.  The  same  fact  may  be  proved  by  exposing 
to  the  air  equal  quantities  of  the  same  liquids  in  vessels  of  equal 
size ;  the  ether  will  disappear  with  the  greatest  rapidity,  water 
with  the  least ;  and  those  liquids  will  be  found  to  evaporate 
with  the  greatest  rapidity  whose  boiling  point  is  the  lowest. 
Most  liquids  are  susceptible  of  this  gradual  dissipation,  and  even 
so  ne  solids  such  as  camphor  and  ice,  both  of  which  waste  away 
when  exposed  to  the  air, without  undergoing  liquefaction.  That 
mercury  evaporates,  may  be  shown  by  suspending  a  bit  of  gol  I 
leaf  in  a  bottle  partly  filled  with  this  liquid ;  in  a  few  weeks  the 

2r>4.  Is  the  rate  of  evaporation  of  different  liquids  in  the  air,  as  well  as  in  a  vacuum, 
Prove  this  by  experiment. 


180 


THE  BULK  OF  AIR  AFFECTED  BY  VAPOR. 


lower  part  of  the  gold  leaf  will  become  white  from  the  conden- 
sation of  the  vapor  of  mercury  upon  it.  In  general,  the  pro- 
cess of  evaporation,  for  every  liquid,  goes  on  precisely  the  same 
in  air  as  in  a  vacuum,  except  in  rapidity.  In  the  case  of  a 
vacuum,  the  vessel  acquires  the  full  complement  of  vapor  due 
to  the  temperature  instantaneously ;  in  the  case  of  air,  there  is 
a  mechanical  impediment  to  the  rise  of  vapor  which  retards  the 
process,  but  eventually  the  vessel  will  contain  the  same  quantity 
of  vapor  when  the  thermometer  is  at  the  same  height,  whether 
it  be  empty,  or  full  of  air. 

205.  The  presence  of  Vapor  in  Air  affects  its  bulk  and  den- 
sity. When  a  liquid  evaporates  into  the  air  contained  in  an 
open  flask,  a  portion  of  the  air  is  expelled,  in  consequence  of 
the  additional  bulk  imparted  to  it;  and  the  gaseous  contents 
of  the  flask  will  consist  of  a  mixture  of  air  and  the  vapor  of 
the  evaporating  liquid.  Whether  these  gaseous  contents  gain 
in  weight,  or  not,  will  depend  upon  the  density  of  the  vapor  in 
question ;  if  it  be  lighter  than  air,  the  gaseous  contents  of  the 
flask  will  weigh  less  than  before ;  if  heavier,  they  will  weigh 
more.  Watery  vapor  is  considerably  lighter  than  air,  and  con- 
sequently air,  saturated  with  moisture,  weighs  considerably  less 
than  perfectly  dry  air;  this  maybe  one  reason  of  the  fall  of  the 
barometer  just  previous  to  a  storm,  viz.,  the  gradually  increas- 
ing quantity  of  watery  vapor  in  the  air.  If,  on  the  other  hand, 
the  vapor  of  the  liquid  be  heavier  than  air,  as  in  the  case  of  the 
vapor  of  bromine,  the  weight  of  the  gaseous  contents  of  the  flask 
will  be  increased,  and  it  will  support  a  higher  mercurial  col- 


umn. 


Table  of  density  of  Vapors  at  the  boiling  point  of  their  liquids  respect- 
ively compared  with  that  of  Air. 


Air, 1.000 

Steam, 0.6235 

Alcohol, 1.6138 

Ether, 2.5860 


Bi-Sulphide  Carbon,    .     .  2.6447 

Spirit  of  Turpentine,  .     .  3.0130 

Mercury, 6.976 

Iodine,  8.716 


From  this  table  it  is  apparent  that  the  density  of  steam,  at 
212°,  and  of  watery  vapor  in  general,  is  much  less  than  that  of 
aSr.  This  fact  explains  the  rapid  rise  of  steam  in  the  air  when 
discharged  from  the  escape  pipe  of  a  steam  engine. 


205.  What  effect  has  the  presence  of  watery  vapor  in  the  air  upon  its  bulk  and  density  ? 
Why  does  moist  air  weigh  less  than  an  equal  bulk  of  dry  air?  What  effect  has  the 
moisture  in  the  atmosphere  upon  the  height  of  the  mercury  in  the  barometer? 


CIRCUMSTANCES    INFLUENCING    EVAPORATION.  181 

206.  Circumstances  which  influence  evaporation.       The 

same  liquid  evaporates  with  different  degrees  of  rapidity  at  dif- 
ferent times.  The  circumstances  which  chiefly  influence  evapo- 
ration are,  extent  of  surface,  and  the  state  of  the  air,  as  to  tem- 
perature, dryness,  stillness,  and  density. — 1st.  Extent  of  Sur- 
face. As  evaporation  takes  place  only  from  the  surface  of 
liquids,  it  is  obvious  that  its  rapidity  must  depend  upon  the  ex- 
tent of  surface  exposed ;  a  given  quantity  of  water  will  evapo- 
rate four  times  as  quickly  from  a  vessel  two  feet  square,  as  it 
will  from  a  ves.sel  one  foot  square. — 2d.  Temperature.  The 
effect  of  heat  in  hastening  evaporation  may  be  shown  by  put- 
ting an  equal  quantity  of  water  in  two  saucers,  one  of  which  is 
placed  in  a  warm,  the  other  in  a  cold  situation;  the  former  will  be 
quite  dry  before  the  liquid  in  the  other  is  perceptibly  diminished. 
Klevation  of  temperature  in  the  air,  in  the  evaporating  liquid,  and 
in  the  vessel  containing  it,  always  quickens  evaporation. — 3d. 
Slate  of  the  air  as  to  moisture  and  dryness.  As  the  amount  of 
vapor  which  can  exist  in  the  air  is  limited,  and  depends  upon 
its  temperature,  it  is  evident  that  if  the  air  be  saturated  with 
moisture,  no  more  can  be  evaporated,  and  that,  in  proportion  as 
it  approaches  saturation,  must  the  process  of  evaporation  be  re- 
tarded. Whereas,  if  the  air  contain  but  little  vapor,  it  can 
readily  take  up  a  large  additional  amount,  and  the  process  of 
evaporation  must  be  proportionably  hastened.  In  dry,  cold 
days,  in  winter,  the  evaporation  is  exceedingly  rapid ;  whereas, 
if  the  air  conta'n  much  moisture,  it  proceeds  very  slowly,  even 
though  the  air  be  warm. — 4th.  Stillness  of  the  air.  Evaporation 
is  much  slower  in  still  air  than  in  a  current.  The  air  immedi- 
ately in  contact  with  the  water  becomes  saturated  with  vapor, 
and  a  check  is  soon  put  to  evaporation  ;  if,  however,  the  air  be 
removed  as  fast  as  it  has  become  charged  with  vapor,  and  its 
place  supplied  with  fresh,  dry  air,  the  evaporation  continues 
without  interruption.  This  is  the  rea-on  why  evaporation  pro- 
ceeds writh  so  much  rapidity  upon  a  windy  day. — 5th.  Pressure 
has  also  a  marked  effect  upon  evaporation ;  if  the  atmospheric 
pressure  be  diminished,  evaporation  goes  on  more  rapidly,  be- 
cause there  is  less  resistance  to  be  overcome  ;  on  the  other  hand, 
increase  of  pressure,  by  increasing  the  resistance  to  be  over- 
co.ne,  tends  to  retard  the  process. 

207.  Absorption  of  Heat  in  Evaporation.— Diminution  of 
Temperature.    The  most  important  fact  connected  with  evapo- 

206.  State  the  circumstances  which  influence  evaporation      What  is  the  effect  of  extent 
of  surface?    Of  temperature?     Of  moisture  and  dryness?    Of  stillness  ?    Pressure? 


182 


ABSORPTION    OF   HEAT    IN    EVAPORATION. 


Fig.  86. 


ration,  as  with  ebullition,  is  the  absorption  and  disappearance 
of  a  large  amount  of  heat ;  and  what  strikes  one  at  first  as  very 
singular,  more  heat  is  absorbed  in  this  process  than  when  water 
bo:ls  at  212°.  For  it  has  been  found  that  the  lower  the  tem- 
perature at  which  a  vapor  is  formed,  the  greater  the  amount  of 
its  latent  heat ;  and  that  the  sum  of  the  insensible  and  sensible 
heat  in  vapor  formed  at  all  temperatures  is  very  nearly  a  con- 
stant quantity  ;  the  higher  the  sensible  heat  of  vapor,  the  smaller 
the  amount  of  its  insensible  heat,  and  the  lower  the  sensible 
heat,  the  larger  the  amount  of  'its  insensible  heat.  Thus,  a  cer- 
tain weight  of  vapor  at  100°,  condensed  in  a  receiver  contain- 
ing water  at  32°,  gives  out  according  to  Clement  §187,  p.  157. 

Sensible  heat, 68°. 

Latent  heat, 1062°.     Total,  .  .  1130°. 

The  same  weight  of  vapor  at  212°,  condensed  at  82°,  gives  out 

Sensible  heat, 180°. 

Latent  heat, 950°.     Total,  .  .   1130°. 

It  is  quite  evident,  then,  that  the 
vapor  formed  at  100°  contains  more 
latent  heat  than  the  vapor  at  212°, 
in  the  proportion  of  1062°  to  950°. 
In  consequence  of  the  large  amount 
of  heat  absorbed  in  evaporation,  the 
temperature  of  the  evaporating  liquid 
is  inui-h  reduced,  and  great  cold  is  the 
result.  The  fact  of  the  absorption  of 
heat,  and  of  the  production  of  cold  by 
evaporation,  can  readily  be  proved 
by  pouring  a  little  ether  on  the  hand, 
or  on  the  bulb  of  a  thermometer  cov- 
ered wish  linen,  Fig.  86.  The  more 
volatile  the  liquid,  and  the  more  the 
process  be  hastened  by  artificial 
means,  the  greater  the  degree  of  cold. 
Consequently,  ether  produces  a  great-. 
er  degree  of  cold  than  water  or  alco- 
hol, and  if  a  current  of  air  be  blown 
over  it,  the  cold  becomes  sufficiently 
intense  to  freeze  water  without  ditfi- 

Cold  produced  by  Evaporation.         Culty. 

207.  What  is  the  most  striking  fict  connecter!  with  evaporation?  Is  the  absorption 
of  heat  more,  or  less,  than  in  ebullition  ?  What  effect  has  evaporation  upon  tempera- 
ture ?  llow  can  this  fact  be  proved  ? 


0 


THE  CAUSE  OF  THE  COLD  183 

208.  Removal  of  atmospheric  pressure  hastens  Evapo- 
ration and  increases  the  intensity  of  the  Cold.  It  has  been 
shown  that  water  boils  at  a  lower  temperature,  and  with 
much  greater  rapidity,  when  the  atmospheric  pressure  is  dimin- 
ished ;  and  if  the  pressure  of  the  atmosphere  be  entirely  re- 
moved, water  may  even  be  made  to  boil  at  70°,  i.  e.,  142° 
be'ow  its  ordinary  point  of  ebullition ;  for  the  same  reason  the 
rapidity  of  evaporation  is  greatly  increased  by  the  diminution 
of  the  atmospheric  pressure,  and  it  becomes  most  rapid  when 
this  pressure  is  entirely  removed  by  the  use  of  the  air 
pump.  The  more  rapid  the  evaporation,  the  greater  is  the  de- 
gree of  cold  produced.  In  the  open  air,  the  cooling  effects  pro- 
duced by  the  evaporation  of  water  are  not  strikingly  apparent, 
because  the  process  is  comparatively  slow,  and  therefore  the 
quantity  of  heat  abstracted  from  any  substance  by  the  vapor,  in 
any  given  time,  is  but  little  more  than  it  receives  from  surround- 
ing objects ;  its  temperature,  therefore,  is  but  slightly  diminished. 
But  when  water  is  placed  in  a  vacuum,  its  evaporation  is  very 
r.ipid,  and  did  not  the  vapor  speedily  completely  fill  the  vacuum, 
and  thus  prevent  further  evaporation,  its  temperature  would 
soon  sink  low  enough  to  freeze.  If  the  vapor  that  rises  from 
the  water  be  removed  as  coon  as  it  is  formed,  by  some  substance 
placed  within  the  receiver  whi;'h  has  a  strong  chemical  affinity 
for  water,  like  sulphuric  acid,  or  chloride  of  calcium,  so  that  the 
completeness  of  the  vacuum  is  permanently  maintained,  water 
can  readily  be  frozen  by  its  own  evaporation.  In  Fig.  87,  the 
upper  pan  is  filled  with  water,  and  the 
Fig.  87.  lower  with  sulphuric  ac:d ;  the  wate-y 

vapor  is  absorbed  by  the  latter  nearly  as 
fast  as  it  is  formed,  and  a  gentle  work- 
ing of  the  pump  is  generally  sufficient 
to  freeze  the  water  in  a  few  moments. 
Or,  if  water  be  placed  in  sma!l  quan- 
tity, as  a  drop,  for  instance,  upon  a  piece 
of  cork,  or  some  other  substance  of  poor 
conducting  power  for  heat,  so  that  it  will 
not  readily  supply  to  it  the  heat  which 
Water  freezing  in  a  Vacuum,  is  carried  off  in  evaporation,  the  drop 
of  wa'cr  m  ly  be  easily  frozen  under 
the  exhausted  receiver  of  an  air  pump.  In  Fig.  87,  if  the  up- 

208.  What  effect  has  the  removal  of  atmospheric  pressure  upon  the  degree  of  cold  ? 
Show  how  water  may  be  frozen  by  the  evaporation  of  ether  under  the  receiver  of  ail  air 
pump.  Show  how  water  may  be  frozen  by  its  o\m  evaporation. 


184  PRODUCED  BY  EVAPORATION. 

per  vessel  be  removed,  a  thermometer  be  placed  in  the  lower 
vessel,  ether  poured  in,  and  a  watch  glass,  containing  a  small 
quantity  of  water,  be  placed  in  the  ether,  as  soon  as  the  exhaus- 
tion of  air  commences,  the  ether  will  begin  to  boil  at  a  tempera- 
ture considerably  below  32°,  and  the  water  will  be  speedily 
frozen.  By  the  application  of  this  principle  water  may  be  frozen 
in  considerable  quantities.  By  an  exhaust  pump,  worked  by 
a  steam  engine,  the  atmospheric  pressure  is  removed  from  the 
surface  of  ether  confined  in  a  metal  cylinder  placed  horizontally 
in  a  tank  of  salt  water.  The  ether  flashes  into  vapor,  taking 
the  heat  necessary  to  its  existence  in  this  condition  from  the 
surrounding  salt  water,  which  is  thus  cooled  down  to  25°. 
Salt  water  is  used  becauce  it  does  not  congeal  at  this  low  point. 
The  salt  water  thus  cooled,  is  then  made  to  circulate  around 
copper  vessels,  tinned  on  the  inside,  and  containing  pure  water, 
which,  in  a  few  moments,  is  frozen  solid.  The  salt  water,  in  per- 
forming this  process,  increases  in  temperature  only  5°  or  6°,  and 
is  returned  by  a  pump  to  the  original  tank,  where  it  is  again 
reduced  to  25°  by  the  evaporation  of  the  ether.  Thus,  by  the 
continual  working  of  the  exhaust  pump,  evaporation  is  effected, 
heat  absorbed,  cold  produced,  and  ice  made  to  the  amount  of 
four  tons  daily.  The  vapor  of  ether  removed  by  the  pump,  is 
conveyed  through  a  spiral  tube,  surrounded  by  a  large  quan- 
tity of  cold  water,  and  condensed  again  into  a  liquid  to  be  used 
a  second  time. 

209.  The  cause  of  the  cold  produced  by  Evaporation.     The 
cause  of  the  reduction  of  temperature  by  evaporation  is  simply 
this: — In  the  change  of  any  substance  from  the  liquid  to  the 
gaseous  state,  a  large  quantity  of  heat  is  absorbed  and  rendered 
latent,  and  this  heat  must  be  supplied  from  the  water  which 
remains  unevaporated.      For  every  drop  of  water  which  is 
vaporized,  the  water  which  is  left  behind  in  the  cup  will  be 
deprived  of  as  much  heat  as  would  be  sufficient  to  raise  the 
temperature  of  a  similar  drop  1000°  if.it  were  to  remain  liquid. 
This  immense  loss  of  heat  reduces  the  temperature  of  the  water 
in  the  cup  to  the  freezing  point,  and  compels  it  to  conceal. 
The  cold  produced  is  due,  therefore,  to  the  large  amount  of  heat 
made  latent  in  the  passage  of  a  substance  from  the  liquid  to  the 
gaseous  state. 

210.  The  Cryophorus.     This  is  a  curious  instrument,  in- 

Describe  the  process  by  which  water  may  be  frozen  upon  a  Inrge  pcale  by  the  evapo- 
ration of  ether.— 209.  State  the  cause  of  the  cold  produced  by  evaporation.— 210.  Describe 
the  Crj  ophorus. 


THE    CRYOPHORUS.  185 

vented  by  Dr.  "Wollaston,  and  intended  to  illustrate  the  freez- 
ing of  water  by  its  own  evaporation.  It  consists  of  two  bulbs 
of  glass  joined  by  a  tube.  One  bulb  is  half  filled  with  water 
and  bo'.led  over  a  lamp.  As  soon  as  the  steam  has  complexly 
filled  .the  whole  apparatus,  and  entirely  expelled  the  air,  through 
an  orifice  left  at  the  extreme  end  of  the  other  bulb,  this  aperture 
is  hermetically  sealed  by  the  blow-pipe.  Nothing,  therefore,  is 
left  within  the  apparatus  but  water  and  watery  vapor ;  if  this 
vapor  ba  condensed,  a  vacuum  is  at  once  produced,  which  of 
course  favors  rapid  evaporation.  To  use  the  apparatus,  all 
the  water  is  made  to  collect  in  one  bulb,  and  the  empty  bulb  is 
then  immersed  in  a  freezing  mixture  of  ice  and  salt,  as  repre- 
sented in  Fig.  88 ;  the  effect  is  to  condense  the  vapor  into  water, 


Tlie  Cryophorus, 

with  the  production  of  a  vacuum,  and  such  a  rapid  evaporation 
from  the  water  in  the  other  bulb,  that  it  is  soon  frozen.  The 
bulb  containing  the  water  is  prevented  from  receiving  heat  from 
surrounding  objects  by  a  jar  covered  with  a  pasteboard  I'd,  as 
represented  in  the  figure.  Instead  of  immersing  the  bulb  in  a 
freezing  mixture,  the  instrument  may  be  mounted  vertically  in 
the  bell  glass  of  an  air  pump,  in  such  a  way  that  its  empty 
bulb  may  dip  into  a  vessel  filled  with  ether,  placed  on  the  plate 
of  the  air  pump,  while  its  tube  passes  through  the  top  of  the 
bell,  and  its  bu'.b  containing  water  is  supported  in  the  air  above. 
Oa  exhausting  the  air  of  the  bell  glass,  the  ether  evaporates, 
cold  is  produced,  the  watery  vapor  in  the  bulb  i->  condensed,  and 
in  a  few  moments  the  water  in  the  upper  bulb  is  frozen  by  its 
own  evaporation  ;  care  should  be  taken  to  protect  it  from  the 
heat  of  surrounding  objects.  The  name  cryophoius  signifies 
frost-producer. 

Show  how  it  may  be  made  to  act  by  insertion  in  an  exhausted  receiver, 


186  THE    PULSE    GLASS. 

211.   The  Pulse  Glass.    This  is  an  instrument  similar  to  the 
cryophorus,  except  that  it  is  partially  filled  with  ether  and  its 

vapor,    instead    of    water. 

Fig  89'  ^n  alin  tne  hand  to 


«  -%  e*.  /7*\xL^«r  iv  v      one  bulb> the  vaP°r  expand- 

jy  ing  drives  all  the  fluid  into 

c        .     y^  the  other  bulb,  and  at  length 

Pulse  Glass.  produces  the  appearance  of 

violent  boiling.  At  this  in- 
stant a  sensation  of  coM  is  experienced  in  the  hand ;  Fig.  89. 
The  boiling  is  produced  by  the  rapid  vaporization,  from  the  Leat 
of  the  hand,  of  the  film  of  liquid  lining  the  inside  of  the  empty 
bulb. 

212.  The  cold  produced  by  Fountains  and  Earthen  Water 
Jars.     Evaporation   is   frequently    employed    to  produce  cold. 
Thus  fountains,  by  throwing  up  a  large  quantity  of  water  in  the 
air,  in  fine  spray  and  drops,  expose  a  large  surface  of  liquid, 
and  the  evaporation  which  this  produces  cools  the  air  very  per- 
ceptibly.    On  the  same  principle,  a  bo'tle  of  wine,  surround*  d 
by  a  piece  of  cotton  or  linen,  wetted  with  water  and  suspended  in 
a  draught  of  air,  will  have  its  temperature  reduced  several  de- 
grees.    The  famous  wine  coolers  used  in   Spain,  called  Alcaz- 
zarras,  depend  on  the  same  principle.     These  are  large  eaitlu  n 
vessels,  made  of  porous  clay,  and  unglazed.     The  bottles  of  wine, 
or  other  substances,  which  it  is  desired  to  cool,  are  placed  in  the 
inside,  and  the  remaining  space  filled  with  water;  owrlng  to  the 
porosity  of  the  clay  the  water  oozes  to  the  outside,  and  evapo- 
rating, soon  reduces  the  temperature  of  the  interior  of  the  jar 
several  degrees.    The  degree  of  cold  produced  is  much  increased 
by  a  current  of  air. 

213.  Effect  of  Evaporation  upon  Animal  Life      Evapora- 
tion takes  place  constantly  from  the  surface  of  our  bodies,  and 
thus  it  assists  powerfully  in  maintaining  the  equable  animal 
temperature  essential  to  comfort  and  health.     The  natural  tem- 
perature of  the  human  body,  in  health,  is  about  98°,  and  it  can 
not  be  raised  much  above  this  po'nt  without  producing  serious 
discomfort,  and   permanent  injury.     Violent  exercise   always 
tend-*  to  increase  the  animal  heat,  but  the  more  violent  it  is  the 
greater  the  quantity  of  perspiration  which  is  poured  forth  uf  on 
the  surface  of  the  skin,  and  the  more  abundant  the  evaporation, 


211.  Describe  the  pulse  glass.— 212.  Explain  the  coolness  produced  by  fountains  and 
water  jars.— 213.  What  is  the  elfect  of  evaporation  upon  the  animal  economy  ? 


EFFECT    OF    EVAPORATION    ON    CLIMATE.  187 

and  consequently,  the  greater  the  amount  of  heat  absorbed  and 
carried  off.  In  this  manner  nature  regulates  the  heat  of  the  sys- 
tem, and  during  health,  sustains  the  equilibrium  of  animal  tem- 
perature. If  this  evaporation  be  checked,  the  temperature  of  the 
system  rises,  fever  supervenes,  and  the  most  injurious  conse- 
quences often  result.  In  summer,  when  the  temperature  of  the 
a:r  is  nearly  as  great  as  that  of  the  human  body,  the  least  exer- 
tion is  attended  with  a  very  great  increase  of  the  animal  tem- 
perature, and  is  inconvenient  and  oppressive ;  but  at  the  same 
time  a  copious  perspiration  is  poured  forth,  the  evaporation  of 
which  not  only  tends  to  carry  off  all  the  superfluous  heat  that 
would  le  injurious  to  the  animal  economy,  but  also  enables  man 
to  perform  much  physical  and  mental  labor,  which  otherwise 
would  be  impossible. 

214.  Effect  of  Evaporation  on  the  temperature  of  the  Earth 
and  on  Climate.    The  effect  of  the  evaporation  of  the  immense 
quantity  of  water,  which  is  continually  taking  place,  is  to  lower 
the  temperature  of  the  earth  and  the  sea,  and  to  prevent  them 
from  becoming  excessively  heated  by  the  powerful  influence  of 
the  sun's  rays.     Were  it  not  for  this,  many  portions  even  of  th  3 
temperate  regions  of  the  earth  would  be  absolutely  uninhabitable 
in  summer.     The  temperature  of  the  atmosphere  is  al  o  lowered 
by  the  same  cause.     A  portion  of  the  heat  required  by  the  vapor 
is  drawn  from  the  air,  as  well  as  from  the  earth  and  the  sea, 
and  thus  it  is  rendered  much  less  oppressive.     The  high  tem- 
perature of  summer  is  mitigated  by  the  passage  of  water  from 
the  liquid  to  the  vaporous  state,  in  the  same  way  as  the  excess- 
ive cold  of  winter  is  moderated  by  the  passage  of  the  water 
from  the  liquid   to  the  solid  state ;  in   the  former  case,  va-t 
amounts  of  heat  become  latent ;  in  the  latter,  vast  amounts  of 
heat  previou-ly  latent,  become  sensible ;  it  is  strictly  true  that 
the  evaporation  of  water  greatly  cools  the  atmosphere,  while 
its  congelation  into  ice  and  snow  powerfully  heats  it. 

215.  The  effect  of  the  condensation  of  the  watery  vapor  cf 
the  air.    As  the  formation  of  watery  vapor  cools  the  air  by  the 
immense  amount  of  heat  which  it  renders  latent,  so  the  conden- 
sation of  this  watery  vapor  into  the  liquid  state  again,  tends 
powerfully  to  heat  the  air,  by  the  immense  amount  of  heat  pre- 
viously latent,  which  it  gives  out.     It  is  estimated  that  one 
Ib.  of  steam  at  212°,  in  undergoing  condensation,  would  raise 
3657  cubic  feet  of  air  10°,  and  cause  it  to  expand,  in  so  doing, 

214.  On  the  temperature  of  the  earth,  and  on  climate ?— 215.  What  is  the  effect  upon 
the  air  of  the  condensation  of  its  watery  vapor  'I 


188      AMOUNT  OF  WATERY  VAPOR  IN  THE  AIR. 

to  3733  cubic  feet.  Every  pint  of  rain  which  falls  indicates 
an  equivalent  expansion.  This  is  also  the  reason  why,  in 
the  very  cold  weather  of  winter,  the  temperature  of  the  atmo- 
sphere rises  the  instant  a  violent  snow  or  rain  storm  commences. 

216.  The  amount  of  watery  vapor  contained  in  ike  air. 
The  amount  of  watery  vapor  contained  in  the  air  is  enormous. 
It  is  estimated  to  be  at  least  50,000,000,000,000  tons.  The 
total  annual  fall  of  rain  is  estimated  at  188,452,000,000,000 
tons.  The  whole  of  this  vast  quantity  is^  raised  into  the  air 
from  the  waters  of  the  ocean  by  the  process  of  evaporation,  and 
this  shows  that  the  process  is  carried  on  upon  an  immense  scale. 
It  has  been  estimated  that  in  summer  the  number  of  pounds 
evaporated  from  the  surface  of  water,  under  favorable  circum- 
stances, is  104£  per  minute  to  the  acre,  and  the  number  of  gal- 
lons per  acre,  in  24  hours,  is  15,048.  In  consequence  of  this, 
the  atmosphere  is  at  all  times  charged  with  vapor,  the  amount 
of  which  is  perpetually  varying,  but  it  is  almost  always  below 
the  proportion  which  the  atmosphere  might  contain  if  it  were 
loaded  with  as  much  moisture  as  it  could  possibly  hold  at  its 
actual  temperature.  It  is  owing  to  the  circumstance  that 
the  air  is  seldom  thoroughly  saturated  with  watery  vapor,  that 
wet  bodies  become  dry,  and  that  the  surface  of  the  eoll,  how- 
ever moist  it  may  be,  in  a  very  brief  period  becomes  parched 
and  dusty.  By  this  process  of  evaporation  a  natural  distillation 
is  maintained,  by  which  a  perpetual  circulation  of  water  is  kept 
up.  The  water  is  raised  in  a  perfectly  pure  state  into  the  at- 
mosphere, is  transported  to  distant  regions,  and  being  condensed 
in  rain,  not  only  falls  upon  the  land  in  grateful  showers,  but  also 
carries  with  it  various  gaseous  products  useful  to  vegetation, 
such  as  Ammonia  and  Nitric  acid,  which  are  diffused  through  it. 
The  waters  thus  condensed,  descend  through  the  valleys  into 
the  rivers,  whence  they  are  returned  to  the  ocean,  or  else  sink- 
ing into  the  earth  eventually  reappear  as  springs.  Were  it  not 
for  this  process  the  earth  would  be  destitute  of  rain,  and  a  des- 
ert, producing  no  vegetation,  and  incapable  of  supporting  animal 
life.  If  evaporation  were  to  cease,  all  living  things  would  per- 
ish ;  there  would  be  no  rivers  or  brooks ;  no  clouds  or  brilliant 
sunrises,  or  sunsets ;  the  earth  would  be  shorn  of  its  beauty,  as 
well  as  deprived  of  life. 

217.    Hygrometers.    The  quantity  of  watery  vapor  existing 

215.  State  the  amount  of  watery  vapor  contained  in  the  air.  What  is  the  amount  of 
evaporation  from  the  surface  of  water  per  acre  ?  What  becomes  of  the  water  raised  jiito 
the  air  by  evaporation  ?  State  the  advantages  of  this  process  of  natural  distillation,. 


SAUSSURE'S  HYGROMETER. 


180 


Fig.  90. 


in  the  air  at  any  particular  time,  depends  entirely  upon  the 
temperature,  other  things  being  equal,  and  the  exact  amount 
can  be  ascertained  by  an  instrument  called  the 
hygrometer.  These  are  constructed  upon  very 
different  principles.  One  of  the  simplest  is 
the  hygrometer  of  Saussure,  which  depends 
upon  the  property  possessed  by  hair,  of  length- 
ening in  moist,  and  contracting  in  dry  air. 
A  single  hair  is  fastened  firmly  by  one  end,  and 
art  the  other  is  wound  once  or  twice  around  an 
axle  carrying  an  index.  As  it  contracts  or  ex- 
pands, it  causes  the  index  to  traverse  a  gradu- 
ated circle,  a  greater  or  less  distance,  and  thus 
it  furnishes  an  approximate  indication  of  the 
amount  of  the  moisture  present  in  the  atmos- 
phere; Fig.  90.  A  thermometer  is  also  at- 
tached to  the  instrument  for  the  purpose  of 
indicating  the  temperature  of  the  atmosphere 
at  the  time  when  the  observation  is  taken. 

218.  Banieirs  Hygrometer.  This  is  a 
more  accurate  instrument  than  the  last.  It 
consists  of  two  bulbs,  one  of  which  is  half  fi.lcd 
with  liquid  ether,  while  the  other  bulb  and  the 
tube  connecting  them  contain  nothing  but  the 
vapor  of  the  same  substance.  The  bulb  A 
encloses  a  thermometer,  for  the  purpo  e  of  indicating  its  tem- 
perature ;  the  bulb  B  is  enveloped  with  muslin.  There  is  a 
second  thermometer  for  the  purpose  of  indicating  the  tempera- 
ture of  the  atmo-phere.  The  principle  on  which  the  instru- 
ment acts  i.*,  that  when  the  atmosphere  contains  as  much  mois- 
ture as  it  can  hold  at  the  particular  temperature  which  it  pos- 
sesses, a  very  slight  reduction  of  temperature  will  cause  a  portion 
of  this  vapor  to  be  deposited  in  the  form  of  water.  When  the 
air  does  not  contain  as  much  vapor  as  it  can  hold  at  its  actual 
temperature,  it  must  be  reduced  to  tint  at  which  the  vapor  con- 
tained in  it  will  be  sufficient  to  saturate  it,  before  any  will  be 
deposited;  and  this  reduction  will  be  more  or  less,  according  to 
the  degree  of  saturation  of  the  air.  The  number  of  degrees, 
therefore,  which  the  temperature  of  the  atmo-phere  must  be 
reduced  before  it  will  deposit  its  watery  vapor,  is  then  a  meas- 


217.  How  may  the  degree  of  moisture  in  the  atmosphere  be  ascertained?    What  are 
Hygrometers  ?— 218.  Describe  Daniell's  Hygrometer. 


?»  HILL'S  IIYGROITETEU. 


Hygrometer  of  Daniett. 


i-'  cl>  ure  of  the  amount  of  vapor  in 

the  air.  To  use  this  hygrome- 
ter, we  first  note  the  tempera- 
ture of  the  air,  by  the  thermome- 
ter on  the  stem  of  the  instru- 
ment. We  then  pour  sulphuric 
ether,  drop  by  drop,  on  the  mus- 
lin. By  its  evaporation  it  cools 
the  bulb  B,  and  condenses  a  por- 
tion of  the  vapor  within  it;  a 
partial  vacuum  is  formed  in  A, 
in  consequence  of  which  the 
ether  in  it  begins  to  evaporate 
rapidly,  and  its  temperature,  ai:d 
that  of  the  whole  bulb,  to  sink, as 
indicated  by  its  thermometer. 
Presently,  a  degree  of  cold  is 
attained  at  which  the  outsi<!e  of 
the  bulb  becomes  suffused  with 
a  fine  dew ;  at  this  instant  we 
note  the  thermometer  in  the 
bulb  and  observe  the  difference 

between  it  and  the  thermometer  on  the  s-tem.  This  gives  us  the 
number  of  degrees  which  it  has  been  necessary  to  reduce  tl.e 
temperature  of  the  air,  in  order  to  make  it  part  with  its  mois- 
ture, and  as  a  consequence  the  amount  of  vapor  contained  in 
the  atmosphere.  As  it  is  possible,  if  the  reduction  of  tempera- 
ture has  been  rapid,  that  the  loss  of  heat  may  not  have  been 
perfectly  uniform  throughout  the  interior  of  the  bulb  A,  and  tho 
thermometer  in  it  not  have  become  cooled  as  eoon  as  the  outside 
surface  of  the  bulb,  it  is  well  to  observe  the  tcmpeiature  of  A 
a  second  time,  at  the  moment  when  the  ring  of  dew  disap- 
pears, during  the  return  of  the  instrument  towards  the  tcmpeia- 
ture  of  the  surrounding  air.  The  temperature  at  which  the 
dew  is  formed  and  disappears,  is  called  the  dew  point,  and  the 
mean  of  these  two  observations  will  give  it  with  perfect  exact- 
ness. By  means  of  a  table  constructed  for  the  purpose,  the 
degree  of  saturation  of  the  air  can  be  calculated,  the  dew  point 
having  once  been  ascertained.  Let  the  temperature  of  the  air 
be  60°,  and  the  dew  point  50°,  calling  1000  the  amount  of 
watery  vapor  which  the  air  can  possibly  hold  at  GO0,  and  ob- 
serving from  the  table  that  the  tension  of  watery  vapor  at  CO0 
is  0.518,  while  at  50°  it  is  0.361,  and  knowing  that  the  quantity 


EFFECT  OF  REDUCING  THE  TEMPERATURE  OF  THE  AIll  101 

of  vapor  is  directly  proportioned  to  its  tension,  we  have  this 
proportion:  0.518:0.361 ::  1000 :x.  =  695.  The  proportion  of 
watery  vapor  actually  contained  in  the  air,  to  that  which  it  might 
contain  at  the  temperature  in  question,  is  as  695  to  1000.  Ta- 
bles have  also  been  constructed  for  showing  the  actual  rate  of 
evaporation  at  any  given  time,  or  the  number  of  grains  of  water 
wrhich  will  evaporate  from  a  given  surface,  such  as  a  square 
foot,  freely  exposed  to  the  air  in  a  certain  time,  for  it  is  this 
which  determines  the  drying  influence  of  the  atmosphere  upon 
substances  exposed  to  its  action. 

219.  The  effect  of  reducing  the  temperature  of  the  air,upon 
the  amount  of  watery  vapor  contained  in  it.     As  the  presence 
of  aqueous  vapor  in  the  air  is  due  to  heat,  it  is  evident  that  if 
the  temperature  of  air,  charged  with  moisture,  be  reduced  below 
the  dew  point,  this  vapor  will  be  compelled  to  resume  the  liquid 
state.     This  reduction  of  temperature  is  effected  by  a  variety 
of  natural  causes,  and  results  in  the  production  of  clouds,  of 
rain,  of  snow,  of  dew,  and  of  frost.     When  a  stratum  of  warm 
air,  charged  with  moisture,  is  suddenly  mixed  with  a  stratum  of 
cold  air,  the  amount  of  vapor  being  greater  than  the  tempera- 
ture produced  by  the  mixture  can  sustain,  a  portion  is  condensed 
into  rain,  and  if  the  temperature  be  low  enough,  into  snow. 
Again,  if  a  portion  of  air,  charged  with  watery  vapor,  be  car- 
ried from  the  lower  part  of  the  atmosphere  to  the  higher,  its 
volume  will  be  rapidly  increased  by  the  diminution  of' the  atmos- 
pheric   pressure  to  which  it  is  subjected,  and  its  temperature 
will  be  proportionably  lowered.      '1  he  result  will  probably  be 
the  condensation  of  its  watery  vapor,  and  the   production  of 
clouds  and  rain.     On  the  other  hand,  if  air,  contain^  clouds, 
bj  brought  from  the  higher    regions  of  the  atmosphere  to  the 
lower,  its  temperature  will  be  raised  by  the  additional  pressure 
to  which  it  is  subjected,  it  will  be  able  to  sustain  a  larger 
amount  of  water  in   the  state  of  vapor,  and  the  clouds  will 
probably  disappear.     Again,  if  portions  of  air,   charged  with 
moisture,  be  swept  from  the  sea  against  the  cold  sides  of  some 
lofty  mountain,  the   moisture    will   be   at  once  condensed,  and 
descend  in  the  form  of  showers  of  rain. 

220.  Dew  is  produced  by  the  diminution  of  the  temperature 
of  the  air.      Dew  is  nothing  but  the  watery  vapor  of  the    air 
condensed  by  diminished  temperature.     The  cause  of  the  dimi- 

219  What  is  the  effect  upon  the  moisture  of  the  air  of  reducing  its  temperature  ? 
Wh.it  i.s  the  effect  upon  the  watery  vapor  of  the  air  of  increasing  or  diminishing  its  vol- 
ume '  What  is  the  effect  of  transporting  air  from  a  low  to  a  high  point  upon  its  watery 
vapor '-220.  What  is  dew? 


192  OX    TII2    AMOUNT    OF    ITS    WATERY    VAPOR. 

nution  of  the  temperature  of  the  air  is  its  contact  with  bodies 
that  have  been  cooled  by  the  radiation  of  the  heat  of  the  earth 
during  the  night,  arter  the  influence  of  the  sun's  rays  has 
been  withdrawn.  During  the  day,  the  earth  receives  from  the 
sun  more  heat  than  it  radiates,  and  its  temperature  rises ;  but 
as  soon  as  the  sun  begins  to  decline  towards  the  horizon,  this 
process  is  reversed ;  the  earth  then  begins  to  radiate  more  heat 
than  it  receives,  and  its  temperature  rapidly  sinks.  The  air  in 
contact  with  the  earth  is  also  cooled,  and  when  its  temperature 
has  sunk  below  the  degree  necessary  to  retain  its  aqueous  vapor, 
this  vapor  is  condensed  into  minute  drops  of  water,  and  is  de- 
posited upon  the  cooled  surface  of  the  earth.  That  the  cold 
results  from  radiation,  and  not  from  the  general  cooling  of  the 
atmosphere,  is  shown  by  the  fact  that  the  surface  of  the  earth 
is  often  found  to  be  very  cold,  and  to  be  suffused  with  dew, 
when  the  air  above  is  warm  enough  to  retain  all  its  vapor.  •  The 
a'r  a  few  feet  above  the  earth  is  sometimes  warmer  than  the 
surface  of  the  ground  by  20°  or  30°.  Should  the  radiation 
continue  long  enough,  the  dew  is  frozen  as  soon  as  formed,  and 
becomes  frost.  In  some  countries  ice  is  made  in  this  way,  and 
on  this  principle.  Those  substances  which  are  the  best  radia- 
tors of  heat,  are  always  the  most  drenched  with  dew,  because 
they  part  with  the  greatest  amount  of  heat,  and  become  the 
coldest  at  night,  f  uch  as  rough,  dark  and  filamentous  substances, 
while  poor  radiators  have  hardly  any  dew  deposited  upon  them 
at  all.  Rough-leafed  plants  will  be  drenched  with  dew,  while 
smooth  and  polished  leaves  remain  quite  dry.  For  the  same 
reason,  the  former  are  the  soonest  frozen  in  the  fall  of  the  year. 
The  greatest  amount  cf  dew  is  always  deposited  on  clear  and 
moonlight  nights,  because  then  there  is  nothing  whatever  to 
return  to  the  earth  any  portion  of  the  heat  which  it  has  radiated, 
while  on  cloudy  nights  the  clouds  themselves  radiate  back  as 
much  heat  as  the  earth  radiates  to  them,  and  consequently  its  tem- 
perature is  not  sufficiently  reduced  to  admit  of  the  formation  of 
dew.  For  tha  same  reason,  there  is  no  dew  formed  beneath  the 
trees,  or  high  awnings ;  and  thus  it  is,  that  in  the  autumn  a 
thin  covering,  by  preventing  radiation,  protects  plants  from  frost 
even  on  very  severe  nights.  These  facts  are  illustrated  in  Fig. 
92,  where  the  arrows  represent  the  direction  of  the  rays  of  heat. 
Oa  the  left  is  indicated  the  state  of  the  temperature  of  the 

How  is  it  produced?    Show  that  radiation  is  the  cause  of  dew.     Explain  the  effect  of 
clouds  on  the  formation  of  dew. 


THS    PHENOMENA    OF    DEW. 


193 


Phenomena  of  Dew. 

earth  in  the  fall  of  the  year,  produced  by  the  sun's  rays  falling 
on  it,  viz.,  about  53°,  the  air  above  it  being  at  50°.  A  little 
farther  to  the  right  is  represented  the  state  of  things  immedi- 
ately after  sunset,  the  temperature  of  the  earth  having  fallen  to 
43°,  and  the  heat  rapidly  radiating  from  it.  Still  farther  to  the 
right  is  indicated  the  same  process,  a  little  farther  advanced,  the 
earth  cooled  by  radiation  to  33°,  about  the  freezing  point  of 
water,  and  the  atmosphere  above  at  39°.  To  the  right  of  this 
we  observe  the  effect  of  a  cloud,  in  sending  back  the  rays  of 
heat  which  the  earth  had  radiated,  indicated  by  the  reversion 
of  the  arrows.  And  finally,  there  is  seen  the  effect  of  an  awn- 
ing or  covering  in  returning  to  the  earth  the  rays  of  heat  which 
it  had  radiated,  while  the  upper  surface  of  the  awning  or  screen 
itself  is  cooled  down  to  the  freezing  point  by  the  same  process, 
aiid  is  found  in  the  morning  covered  with  frost.  It  is  quite 
evident,  that  the  largest  amount  of  dew  and  frost  must  be 
deposited  upon  bright  and  clear  starlight  and  moonlight  nights ; 
and  in  those  countries  where  the  atmosphere  is  distinguished 
for  its  brightness  and  clearness,  the  reduction  of  temperature 
effected  by  radiation,  is  often  sufficient  to  freeze  considerable 
bodies  of  water.  In  India,  near  the  town  of  Hoogly,  about  40 
miles  from  Calcutta,  the  principle  of  radiation  is  applied  to  the 
artificial  production  of  ice.  Flat,  shallow  excavations,  from  one 
to  two  feet  deep,  are  loosely  lined  with  rice  straw,  or  some  simi- 
lar bad  conductor,  in  order  to  cut  off  the  conduction  of  heat 
from  the  ground,  and  upon  the  surface  of  this  layer  are  placed 
shallow  pans  of  porous  earthenware,  filled  with  water  to  the 
depth  of  one  or  two  inches.  Radiation,  after  the  sun  goes 
down,  rapidly  reduces  the  temperature  below  the  freezing  point, 
and  thin  crusts  of  ice  form,  which  are  removed  as  they  are  pro- 
duced, and  deposited  in  suitable  ice  houses  until  night,  when 
9 


THE    CONSTITUTION    OF    GASES. 

the  ice  is  conveyed  in  boats  to  Calcutta.  "Winter  is  the  ice 
making  season,  viz.,  from  the  end  of  November  to  the  middle 
of  February. 

221.  The  constitution  of  Gases.— Difference  between  Va- 
pors and  Gases.     From  the  above  mentioned  facts  it  is  evident 
that  diminution  of  temperature  has  the  effect  of  condensing 
vapors  into  liquids.     There  are  vapors  not  so  easily  condensed 
as  the  vapor  of  water,  and  which,  at  all  ordinary  temperatures, 
retain  their  aeriform  condition.     These  are  called  gases.     They 
may  be  regarded  as  the  vapors  of  liquids,  which  vaporize  at  a 
degree  lower  than  any  of  the  natural  or  artificial  temperatures 
which  have  been  yet  observed.     In  this  view  oxygen  is  the 
vapor  of  a  liquid,  which  vaporizes  at  a  temperature  vastly  lower 
than  any  yet  discovered.     This  gas,  consequently,  has  never 
been  liquefied.     The  gases  resemble  vapors  in  being  equally 
invisible  and  elastic  aeriform  fluids.     They  differ  from  vapors 
in  this  respect,  that  while  the  gases  obey  the  law  of  Marriotte, 
(§  9,)  at  all  common  temperatures,  and  diminish  in  volume,  and 
increase  in  elastic  force,  as  the  pressure  to  which  they  are  sub- 
jected is  increased ;  vapors,  on  the  other  hand,  at  the  point  of 
maximum  elasticity  for  their  temperature,  if  their  volume  be 
diminished,  are  in  part  changed  into  liquids.     By  a  sufficient 
increase  of  pressure,  combined  with  diminution  of  temperature, 
many  of  the  gases  may,  however,  be  reduced  to  the  state  of 
liquids,  and  then  if  these  liquids  be  allowed  to  evaporate  very 
suddenly,  they  absorb,  in  so  doing,  so  much  heat,  that  a  portion 
of  the  liquid  is  often  frozen.     By  this  process  some  of  the  most 
permanent  gases  have  been  reduced,  first  to  the  state  of  liquids, 
and  then  to  that  of  solids,  a  conclusive  proof  that  the  state  of 
matter,  as  solid,  liquid  and  gaseous,  depends  upon  heat. 

222.  Pressure  required  for    liquefying-     the    Gases.— The 
process.    The  method  of  condensing  the  gases  consists  in  ex- 
posing them  to  the  pressure  of  their  own  elasticity,  continually 
increased  by  the  production  of  fresh  portions  of  gas.     The  pro- 
cess is  exceeding  simple,  and  may  be  performed  by  any  one, 
though  without  care  and  experience,  it  may  be  attended  with 
much  danger  to  the  experimenter.     The  materials  to  form  the 
gas  are  put  into  a  strong  glass  tube,  closed  at  one  end,  and  bent, 
as  in  Fig.  93 ;  after  which  the  orifice  is  hermetically  sealed,  or 
closed  by  means  of  a  metallic  cap,  strongly  cemented.     In  most 
instances,  it  is  necessary  that  the  materials  should  be  kept  apart 

221.  What  are  gases  ?    State  the  difference  between  vapors  and  gases.  —222.  Show  how 
gases  may  be  condensed  into  liquids. 


THE  CONDENSATION  OF  GASES.  195 

Fig.  93.  until  the  tube  is  closed, 

and  afterwards,  by  a 
change  of  position,  be 
brought  to  act  upon  each 
other.  Thus,  in  order  to 

Liquefaction  of  Gases.  produce  carbonic  acid  gas, 

diluted  sulphuric   acid    is 

poured  into  the  tube,  and  then  pieces  of  chalk  or  marble  are 
introduced;  after  the  end  of  the  tube  has  been  hermetically 
sealed  by  melting  the  glass  with  a  blow-pipe,  taking  care  to 
keep  the  tube  in  the  position  shown  in  the  figure,  the  apparatus 
is  inverted,  the  sulphuric  acid  immediately  descends  upon  the 
marble,  and  the  carbonic  acid  gas  is  instantly  evolved.  Marble 
is  a  compound  of  carbonic  acid  gas  and  lime ;  the  sulphuric 
acid,  however,  having  a  stronger  affinity  for  the  lime,  seizes 
upon  it,  and  at  the  same  moment  drives  the  carbonic  acid  out. 
Every  fresh  portion  of  gas  produced  tends  to  compress  that 
which  existed  in  the  tube  before,  and  the  gaseous  particles 
finally  become  so  closely  forced  together,  and  condensed,  as  to 
pass  from  the  gaseous  into  the  liquid  state. 

223.  The  amount  of  pressure  required  varies  with  the  Gas. 
The  amount  of  pressure  required  to  liquefy  the  different  gases 
is  variable.  Thus  sulphurous  acid  gas  requires  only  the  press- 
ure of  two  atmospheres,  or  30  Ibs.  to  the  square  inch,  at  the 
temperature  of  45°  ;  carbonic  acid  gas  requires  thirty-six  atmo- 
spheres, or  450  Ibs.  to  the  square  inch,  at  a  temperature  of  32°  ; 
while  the  gaseous  protoxide  of  nitrogen  requires  no  less  than  fifty 
atmospheres,  or  a  pressure  of  750  Ibs.  to  the  square  inch.  Sup- 
pose, then,  that  the  area  presented  by  the  interior  of  the  tube 
be  eight  square  inches,  the  total  pressure  upon  the  inside  of 
the  tube,  in  which  the  protoxide  of  nitrogen  is  condensed, 
is  750X8  =  6000  Ibs.  This  is  a  force  which  few  glass  tubes 
are  capable  of  resisting.  The  process  is  greatly  expedited  if 
the  end  of  the  tube  containing  the  gas  in  question  is  immersed 
in  a  mixture  of  ice  and  salt ;  this  maintains  a  steady  tempera- 
ture of  — 4°,  and  tends  to  bring  the  particles  of  gas  still  nearer 
together.  Sometimes,  two  separate  vessels,  connected  by  a 
tube,  are  employed,  one  to  hold  the  materials  for  producing  the 
gas,  the  other  to  condense  it.  In  this  case,  the  former  is  called 
the  generator,  the  latter  the  receiver. 


223.  Is  the  pressure  required  the  same  for  all  gases  ?    What  is  the  degree  of  pressure 
often  required?    How  may  the  process  be  expedited? 


196 


THE    SOLIDIFICATION 


224.    Thiloricr's  process  for  solidifying1  Carbonic  Acid.     By 

the  application  of  these  principles  Thilorier,  a  French  philoso- 
pher, was  enabled  not  only  to  liquefy  carbonic  acid,  but  actually 
convert  it  into  a  solid.  In  this  apparatus,  both  pressure  and 
reduction  of  temperature  are  employed  to  liquefy  the  gas,  and 
the  solidification  is  accomplished  by  allowing  a  portion  of  the 
liquid  acid  to  evaporate  very  suddenly ;  so  much  heat  is 
absorbed  that  a  portion  of  the  liquid  acid  is  frozen  and  condensed 
into  white,  flaky  solid,  resembling  snow.  The  apparatus  repre- 
sented in  Fig.  94,  is  the  form  in  which  it  has  been  arranged  by 
Deleuil  &  Son,  of  Paris.  Two  very  strong  vessels  are  provided, 
made  of  the  best  cast  iron,  enclosed  in  a  wrought  iron  casing, 

Fig.  94. 


The  Solidification  of  Carbonic  Acid. 

and  strongly  hooped.  One  is  used  as  the  generator  of  the  gas, 
the  other  as  the  condenser ;  but  as  they  are  made  of  the  same 
size,  and  exactly  alike,  each  may  be  used  equally  well  for  either 
purpose.  The  tube  a  b  e,  can  be  removed  at  pleasure,  and 
the  iron  stoppers  screwed  into  the  top  of  the  cylinders  can  be 
unscrewed  by  the  handles,  e,  e.  In  g  there  is  placed  1800 

224.  Describe  Thilorier's  process  for  solidifying  carbonic  *eid. 


OF    CARBONIC    ACID.  197 

grammes,  or  about  4  Ibs.  of  the  best  bicarbonate  of  soda,  and 
upon  this  about  14  gallons  of  water  at  the  temperature  of  100°  F. 
The  vessel,  h,  is  then  filled  with  strong  sulphuric  acid,  and  care- 
fully lowered  into  the  generator,  an  entrance  having  previously 
been  made  for  the  rod,  i,  through  the  soda,  by  means  of  a  long 
stick.  The  stopper,  e,  e,  is  then  to  be  replaced  and  forcibly 
screwed  down.  On  oscillating  the  generator,  which  can  readily 
bi  done  in  consequence  of  its  suspension  upon  pivots,  the  sul- 
phuric acid  is  thrown  from  the  brass  vessel,  h,  upon  the  bicar- 
bonate of  soda,  which  is  a  compound  of  carbonic  acid  and  soda, 
and  having  a  superior  affinity  for  the  soda,  it  seizes  upon  it,  dis- 
possessing the  carbonic  acid,  which  escapes  in  the  form  of  gas, 
and  collects  in  the  upper  part  of  the  vessel,  where  it  soon  com- 
mences to  compress  itself  most  powerfully.  About  7  minutes 
is  the  estimated  time  for  the  completion  of  the  chemical  reac- 
tion. The  carbonic  acid  is  in  part  liquefied  by  the  great  press- 
ure to  which  it  is  subjected,  and  mixed  with  the  water,  &c., 
used  in  its  preparation.  The  tube,  a,  &,  <;,  is  now  to  be  screwed 
into  its  place  upon  the  top  of  the  receiver,  r,  and  then  firmly 
attached  in  a  similar  manner  to  the  generator,  g.  The  receiver 
is  shown  in  section,  and  it  will  be  observed  that  the  tube,  r, 
leading  from  the  generator,  reaches  to  the  lower  part  of  it.  Up 
to  this  time  there  is  no  connection  between  the  two  vessels.  A 
stop-cock  is  now  opened  upon  the  summit  of  g,  and  a  second 
upon  r,  by  means  of  keys  not  shown  in  the  figure,  and  a  con- 
nection formed  between  the  two  vessels.  The  receiver  being 
colder  than  the  generator,  the  gas  rushes  into  it  with  force,  and 
is  partially  condensed  into  a  liquid  around  the  lower  part  of  the 
tube,  r.  This  condensation  is  produced,  partly  by  the  pressure 
of  the  gas,  and  partly  by  the  difference  between  the  tempera- 
tures of  the  generator  and  receiver.  The  temperature  of  the 
generator  is  from  90°  to  100°,  while  that  of  the  receiver  is  not 
greater  than  that  of  the  surrounding  air,  or  about  GO0.  The 
pre-sure  of  the  carbonic  acid  corresponding  to  the  former  tem- 
perature is  75  atmospheres,  while  that  corresponding  to  the  lat- 
ter is  only  50.  Consequently,  according  to  the  principle  laid 
down  in  §  203,  as  soon  as  a  connection  is  formed  between  the 
two  vessels,  the  carbonic  acid  rushes  over  into  the  receiver,  and 
continues  to  do  so  umil  the  pressure  in  both  vessels  corresponds 
to  that  which  is  proper  to  the  temperature  of  the  receiver. 
The  result  is,  that  in  the  space  of  a  minute,  the  greater  part 

Explain  the  intense  cold  produced  by  the  evaporation  of  the  liquid  acid.. 


198  EXPERIMENTS    WITH 

of  the  carbonic  acid  in  the  generator  is  transferred  to  the  re- 
ceiver. The  quantity  condensed  may  be  greatly  increased  by 
placing  the  receiver  in  a  cask,  and  surrounding  it  with  ice  and 
salt,  having  the  temperature  or  — 4°.  The  stop-cocks  are  thei 
c'o-ed,  the  tube,  a,  &,  c,  removed,  the  stop-cock  of  the  genera- 
tor opened,  and  the  gas  remaining  in  it  suffered  to  escape.  The 
stopper  is  then  to  be  unscrewed,  and  the  interior  of  the  genera- 
tor cleansed.  It  is  then  to  be  charged  anew,  and  the  whole 
process  is  to  be  repeated  seven  times,  when  about  half  a  gallon 
of  liquid  acid  will  be  collected.  With  each  repetition,  more  of 
the  gas  is  liquefied  in  the  receiver,  where  it  at  length  creates 
prodigious  pressure.  The  escape  pipe,  o,  is  then  to  be  adjusted 
to  the  stopper  of  the  receiver,  and  its  end  inserted  into  the  cir- 
cular brass  box,  /,  through  the  tube,  n ;  m,  m,  are  the  two  op- 
posite sides  of  the  box,  which  can  be  firmly  fastened  together 
by  a  simple  arrangement.  The  stop-cock  of  r  is  then  to  le 
opened,  when  the  liquid  acid,  tending  strongly  to  assume  tl.e 
gaseous  state,  will  be  driven  forcibly  through  the  tube  into  the 
brass  box,  and  then,  suddenly  expanding,  FO  much  of  its  heat 
becomes  latent  that  a  portion  of  the  still  liquid  acid  is  frozen, 
and  the  box  becomes  filled  with  a  white  snow-like  substance. 
The  temperature  of  the  box  will  be  reduced  to — 94°  by  this 
process,  and  its  handles  must  be  covered  with  leather,  or  other 
non-conducting  substance,  in  order  to  protect  the  hands  of  the 
operator. 

225.  Solid  Carbonic  Acid.  If  exposed  to  the  air,  the  solid 
acid  slowly  evaporates ;  but  covered  with  cotton,  it  may  be  pre- 
served for  some  hours.  This  is  owing  to  the  extremely  poor 
conducting  power  of  the  solid.  Its  temperature  is  about  — 108° 
or  140°  below  the  freezing  point;  yet,  notwithstanding  this  low 
temperature,  a  mass  of  it  may  be  held  upon  the  hand  without 
producing  any  special  sensation  of  cold ;.  nor  does  a  mercurial 
thermometer,  dipped  loosely  into  it,  exhibit  the  low  temperature 
that  might  be  expected.  This  is  due,  in  part,  to  its  poor  con- 
ducting power,  in  virtue  of  which  the  external  heat  can  not 
readily  en'er  it,  and  in  part  to  its  being  surrounded  by  a  thin 
stratum  of  carbonic  acid  gas,  of  extremely  poor,  conducting 
power.  If  pressed  between  the  fingers,  however,  the  skin  will 
at  onoe  be  blistered,  as  if  scalded ;  and  the  same  result  will  fol- 
low if  it  be  mixed  with  some  liquid  which  is  not  readily  frozen, 

"2^5.  What  is  the  temperature  of  solid  carbonic  acid  ?    Describe  the  experiments  which 
n>av  be  performed  with  it. 


SOLID    CARBONIC    ACID.  199 

like  ether;  this  increases  its  conducting  power  by  filling  up  the 
pores  of  the  acid,  and  greatly  accelerates  the  evaporation.  A 
little  of  this  mixture  placed  upon  the  hand  will  produce  a  deep 
and  painful  blister,  and  almost  immediately  solidify  mercury, 
though  this  requires  a  temperature  of  — 40°  ;  if  a  g^ss  tube, 
containing  liquid  carbonic  acid,  hermetically  sealed,  be  intro- 
duced into  such  a  mixture,  the  acid  will  be  immediately  con- 
gealed. If  some  of  the  frozen  mercury  be  placed  in  water,  the 
mercury  will  melt,  but  the  water  will  be  frozen,  showing  that 
the  process  of  liquefaction,  even  in  the  case  of  frozen  mercury, 
as  in  all  other  instances,  is  attended  with  the  disappearance  of 
heat.  If  the  mixture  of  carbonic  acid  and  ether  be  thrown  into 
a  red-hot  platinum  crucible,  the  whole  mass  will  at  once  be 
thrown  into  the  spheroidal  state,  and  receive  heat  from  the  cru- 
cib'e  so  slowly  that  liquid  mercury  introduced  into  it  in  a  spoo'i, 
will  instantly  be  frozen,  and  may  be  turned  out  upon  the  table 
in  a  solid  form.  The  ether  may  even  take  fire,  and  actually 
blaze  with  a  powerful  flame  from  the  mouth  of  the  crucible,  and 
yet  liquid  mercury  be  frozen ;  this  is  one  of  the  most  extraor- 
dinary experiments  in  chemistry.  By  accelerating  the  evapo- 
ration of  the  bath  of  carbonic  acid  and  ether  in  the  vacuum  of 
the  air  pump,  it  is  said  that  a  temperature  as  low  as  — 166°  F. 
has  been  attained.  By  immersion  in  such  a  bath  many  lique- 
fied gases  have  been  frozen,  and  obtained  in  the  form  of  clear 
and  transparent  solids.  Without  the  aid  of  pressure,  many  of 
the  gases,  including  chlorine,  ammonia,  and  carbonic  acid,  have 
been  obtained  in  the  liquid  form  by  simple  immersion  in  a  bath 
of  carbonic  acid  and  ether  in  air.  The  tubes  used  were  of  green 
bottle  glass,  bent  into  the  form  of  the  letter  V,  and  to  these, 
brass  caps  and  stop-cocks  were  securely  attached,  by  means  of 
a  resinous  cement.  The  cold  bath  was  applied  at  the  curva- 
ture. When  pressure  was  required  it  was  obtained  by  the  em- 
ployment of  two  condensing  syringes. 

226.     The  solidification  of  other  Gases.     The  following  table 
represents  the  point  of  congelation  of  several  of  the  gases : 

Sulphurous  Acid, — 105° 

Cyanogen, —3d9 

lohydrie  Acid, — 60° 

Ammonia,          ........  —103° 

Sulphydric  Acid, — 122P 

Protoxide  of  Nitrogen, — 15<P 

Carbonic  Acid,       -        -        -        -        -        -        -  —70° 

Bromohydric  Acid —124° 

Fluoride  of  Silicon, —  220* 


200 


NATTERER    AND    RITCHIE'3 


Seven  gases,  viz.,  air,  oxygen,  hydrogen,  nitrogen,  carbonic 
oxide,  bi  oxide  of  nitrogen  and  marsh-gas,  have  resisted  all  at- 
tempts to  liquefy  them ;  although  air  was  reduced  to  -gfa  of  its 
bulk,  oxygen  to  ^,  hydrogen  to  -gfai  carbonic  oxide  to 
and  bi-oxide  of  nitrogen  to  F£^  of  its  original  volume. 

226*.  Nattercr's  Process  for  Liquefying-  the  Gases,  Improved 
"by  Bianchi  and  by  Litchie.  In  Thilorier's  process  for  the 
liquefaction  of  carbonic  acid  gas  the  pressure  is  derived  from 
the  continual  production  of  the  gas  within  the  confined  limits  of 
the  generator.  Natterer  shortly  afterwards  invented  an  appa- 
ratus, at  Vienna,  which  has  since  been  improved  by  Bianchi 
at  Paris,  and  still  more  recently  by  our  countryman  Ritchie 
of  Boston,  for  liquefying  this  and  other  liqueti able  gases  by 
direct  mechanical  pressure.  As  constructed  by  him  it  is  showu 
in  section  in  Fig.  92*. 


Fig.  92*. 


Fig.  93*. 


Ritchie's  Condenser. 


The  Discharge  of  the  Liquejied  Gas 


PROCESS    FOR    LIQUEFYING    THE    GASES. 


201 


An  india-rubber  bag  not  seen  in  the  figure,  filled  with  the  gas 
to  be  liquefied,  is  placed  under  a  heavy  weight,  by  which  the 
gas  is  forced  in  a  steady  stream  through  a  bottle  filled  with 
chloride  of  calcium,  by  the  affinity  of  which  for  water  all  the 
aqueous  vapor  of  the  gas  is  abstracted  from  it,  and  it  is  ren- 
dered perfectly  dry.  From  the  drying  bottle  it  passes  on 
through  a  flexible  tube  attached  at  /,  to  a  forcing  pump  by  the 


LIB 


NIYEKS 
CAL1 


Fig.  94*. 


Ritckie'ls  Apparatus  for  Liquefying  Gases. 


piston  of  which  it  is 
compressed  into  a 
strong  iron  condens- 
er R,  through  a  valve 
N,  opening  upwards, 
and  closing  when  the 
piston  descends.  'J  he 
piston  is  driven  by  a 
lever B  placed  below, 
Fig.  94*.  The  con- 
denser R,  is  made  of 
forged  iron  or  bron  ze 
and  is  capable  of  re- 
sisting a  pressure  of 
700  atmospheres. 
The  pump  is  of  steel, 
with  a  steel  piston, 
and  is  attached  to 
the  condenser  by  a 
strong  screw  at  p. 
With  every  stroke 
the  gas  is  more  and 
more  compressed, 
and  finally  is  con- 
verted into  a  color- 
less liquid.  By  this 
powerful  condensa- 
tion the  heat  latent 
in  the  gas  is  made 
sensible,  as  in  the 
case  of  air  com- 


226.  State  the  point  of  congelation  of  other  gases.  Name  the  gases  which  have  resist- 
ed all  attempts  at  solidification. 

2'20*.  Describe  Ritchie's  process  for  liquefving  the  gases  by  mechanical  pressure. 
What  temperature  did  Natterer  succeed  in  obtaining;  by  the  evaporation  of  liquefied 
protoxide  of  Nitrogen  ? 

*9 


202  THE    EVAPOKATION    OF    LIQUEFIED    CASKS, 

pressed  in  the  fire  syringe,  §214,  Fig.  99,  and  the  body  of 
the  pump,  as  well  as  of  the  condenser  is  greatly  heated.  To 
absorb  this  heat,  and  to  assist  in  the  condensation  of  the  gas, 
the  condenser  is  surrounded  by  a  refrigerator  M,  containing 
ice  and  salt,  and  the  pump  is  also  enclosed  in  a  cylinder  M, 
through  which  the  ice  cold  water  from  the  refrigerator  flows,  on 
its  way  to  the  stopcock,  at  which  it  is  discharged.  When  a 
sufficient  quantity  of  the  gas  has  been  liquefied  the  condenser  R 
is  unscrewed  from  the  pump  at  p,  inverted,  and  the  liquefied 
gas  allowed  to  escape  through  the  lateral  aperture  £,  by  turning 
the  screw  at  the  upper  end,  as  seen  in  Fiq.  9  j*.  It  is  received 
in  a  glass  tube  fixed  in  the  stopper  of  a  large  bottle  containing 
a  considerable  amount  of  strong  sulphuric  acid,  that  absorbs 
all  the  watery  vapor  of  the  air  enclosed  in  the  bottle,  and  pre- 
vents the  deposition  of  frost  on  the  outside  of  the  tube,  by 
which  the  view  of  the  liquid  gas  within  would  be  cut  off.  By 
the  rapid  evaporation  of  a  portion  of  the  liquefied  acid  sufficient 
cold  is  produced  to  freeze  the  remainder.  Mr.  Ritchie  has  made 
an  improvement  in  the  construction  of  the  lateral  aperture,  by 
which  it  is  made  to  discharge  liquid  acid,  or  solid  acid,  at 
pleasure.  The  apparatus  is  represented  in  elevation  in  Fig.  94*:  R 
represents  the  bronze  receiver  ;  M,  which  is  shown  in  section, 
represents  the  cylinder  containing  the  ice  and  salt ;  c  is  the 
pump,  and  w  is  the  handle,  by  means  of  which  the  mechanical 
pressure  is  applied,  through  the  instrumentality  of  the  lever  B, 
to  the  piston  p. 

This  apparatus  may  be  used  equally  well  for  the  liquefac- 
tion and  solidification  of  carbonic  acid,  the  protoxide  of  nitro- 
gen and  all  the  other  liquefiable  gases.  By  condensing  the 
gaseous  protoxide  of  nitrogen  into  a  liquid,  mixing  it  with  the 
liquid  bi- sulphide  of  carbon,  and  evaporating  the  mixture  very 
rapidly  m  vacua  in  the  exhausted  receiver  of  an  air-pump, 
Natterer  succeeded  in  producing  a  temperature  of  — 220C>  F., 
which  is  much  colder  than  that  produced  by  the  evaporation  of 
the  mixture  of  solidified  carbonic  acid  and  ether,  §  225,  and  is 
the  lowest  temperature  ever  observed. 

227*.   The  cold  produced  by  the  evaporation  of  the  liquefied 
Gases  applied  to  the  manufacture  of  Ice.     The  liquefied  gase 
being  retained  in  this  state  only  by  the  influence  of  great  pie 
sure,  when  this  pressure  is  removed,  tend  to  evaporate  wi; 

227*.  Show  how  the  liquefied  gases  may  be  used  for  the  manufacture  of  Ice.  Es plain 
this  process  iii  the  case  of  Ammonia. 


APPLi:  D    TO    THE    MANUFACTURE    OP    ICE.  %    3 

extreme  rapidity.  By  this  rapid  change  of  state,  so  much 
heat  is  absorbed  and  made  latent  in  the  immense  amount  of  - 
vapor  which  is  suddenly  formed,  that  the  temperature  of  all 
surrounding  objects  is  greatly  reduced.  It  has  been  shown, 
§  224,  that  it  is  by  the  sudden  evaporation  of  liquefied  carbonic 
acid,  that  the  freezing  of  a  part  of  the  liquid  acid  is  accom- 
plished. The  same  principle  may  be  applied  to  the  freezing 
of  other  liquids,  and  advantage  is  sometimes  taken  of  this 
method  of  reducing  temperature  for  the  manufacture  of  Ice  on 
a  large  scale,  for  commercial  purposes. 

The  gas  usually  selected  for  liquefaction  is  Ammonia.  This 
substance  is  a  compound  of  hydrogen  and  nitrogen,  and  is  rep- 
resented by  the  symbol  NH3.  At  ordinary  temperatures,  it 
is  a  gas,  but  if  expo-ed  to  a  pressure  of  6^  atmospheres,  or 
97^  pounds  to  the  square  inch,  or  to  a  temperature  of — 40° 
F.,  i.  e.  to  72°  below  the  freezing  point  of  water  at  32°  F.,  it  is 
condensed  into  a  clear  liquid,  which  at  — 103°  F.  is  frozen  into 
a  white  crystalline  solid.  When  this  liquid  Ammonia  is  al- 
lowed to  evaporate  intense  cold  is  produced.  For  the  produc- 
tion of  gaseous  Ammonia,  resort  must  be  had  to  some  of  the 
compounds  which  contain  it.  The  most  convenient  substance 
for  this  purpose,  is  the  common  Aqua  Ammonia  of  commerce, 
which  is  nothing  but  a  solution  of  gaseous  Ammonia  in  water. 
"Water  has  the  power  of  absorbing  seven  hundred  times  its 
volume  of  this  gas,  without  undergoing  any  very  great  increase 
in  bulk ;  i.  e.  one  cubic  inch  of  water  will  absorbabout  seven  hun- 
dred cubic  inches 
of  Ammonia,  ow- 
ing to  the  strong  af- 
nity  of  water  for  this 
gas,  and  thus  a  very 
large  amount  of  the 
gas  is,  by  chemical 
means,  compressed 
into  a  very  small 
•^  compass. 

If  this  solution  of 
Ammonia  be  con- 
fined in  one  arm  of 

Liquefaction  of  gaseous  Ammonia  by  pressure  and  cold.  gtronff    bent  tube 

m,  Fig.  95*,  and  exposed  to  a  gentle  heat  over  a  lamp  or  fire, 
the  gas  is  discharged  in  immense  quantities,  and  by  the  power- 


204  CARRE'S 

ful  pressure  which  it  exerts  upon  itself,  and  by  cold,  may 
easily  be  condensed  into  a  liquid  and  distilled  over  info  the 
other  arm  n  of  the  curved  tube,  kept  cool  by  immersion  in  a 
mixture  of  ice  and  salt,  while  the  water  in  which  it  was  dis- 
solved is  left  behind.  If  this  arm  of  the  tube  be  now  taken 
from  the  fire  and  immersed  in  cold  water,  its  temperature 
being  at  once  reduced,  the  force  which  expelled  the  gas  from 
the  water  is  diminished,  and  the  pressure  upon  the  liquefied 
a-nmonia  in  n  is  reduced,  so  that  it  begins  to  evaporate  with 
great  rapidity  back  into  the  arm  m,  where  it  is  immediately 
re-absorbed  by  the  water  from  which  it  had  been  expelled. 
By  the  vacuum  created  by  this  absorption,  an  additional 
amount  of  the  liquefied  gas  in  n  is  allowed  to  evaporate, 
and  so  the  process  goes  on  until  the  whole  of  the  liquefied 
Ammonia  in  n  has  been  re-absorbed  by  the  water  from  which 
it  had  been  expelled  in  m,  and  the  leg  n  is  left  perfet-tly  dry. 
By  this  rapid  evaporation,  the  temperature  of  n  is  greatly  re- 
duced, and  if  immersed  in  water,  while  the  process  is 
going  on,  the  water  is  speedily  frozen.  When  this  has  taken 
place,  the  arm  m  should  be  a  second  time  heated,  the  ammonia 
again  expelled  and  liquefied  in  the  arm  w,  and  then  a  second 
time  evaporated,  and  so  the  process  repeated,  until  all  the  ice 
desired  has  been  produced. 

228*.  Carry's  Ice  Machine.  This  extremely  ingenious  ap- 
paratus is  intended  for  the  manufacture  of  ice  on  a  large 
scale  by  the  liquefaction  and  subsequent  evaporation  of 
gaseous  Ammonia.  It  is  represented  in  Fig.  96*,  and  con- 
sists of  two  parts,  a  generator  A,  and  a  receiver  B.  Aqua  Am- 
monia is  introduced  into  the  generator,  which  is  then  placed 
over  a  fire  and  the  receiver  is  immersed  in  a  vessel  of  cold 
water.  The  gaseous  Ammonia  is  discharged  in  immense  quan- 
tities, and  passing  through  the  valve  o,  Fig.  97*,  opening  up- 
wards, is  conveyed  by  the  tube  d  to  the  receiver  B,  (m  is  a  solid 
rod  intended  to  strengthen  the  apparatus,)  where,  by  the  com- 
bined influence  of  its  own  pressure  and  of  the  cold  of  the  sur- 
rounding water,  it  is  liquefied,  and  collected  in  the  small  recepta- 
cles r,  r,  r.  The  great  heat  which  is  set  free  by  this  liquefaction 
is  immediately  absorbed  and  removed  by  the  cold  water  in 
which  the  receiver  is  placed.  The  process  requires  about  ]  J 
hours  for  completion,  and  is  stopped  as  soon  as  the  thermome- 
ter t  indicates  a  temperature  of  300°  F.  The  apparatus  is 

228*.    Describe  the  first  process  in  Carre's  ice  machine.   Describe  the  second  process. 


ICK    MACHINE. 


205 


then  taken  from  the  fire  and  the  generator  A  placed  in  a  vessel 
of  cold  water,  Fig.  97*.     At  the  same  time  the  vessel  of  cold 

water  is  withdrawn 
from  the  receiver  B, 
and  it  is  exposed  to  the 
natural  temperature  of 
the  air.  A  cylindrical 
cup  containing  the  wa- 
ter to  be  frozen  is  then 
placed  in  the  central 
cavity  E  of  the  receiv- 
er F  and  covered.  As 
the  generator  cools,  the 
internal  pressure  within 
it  and  the  receiver  di- 
minishes, and  the  lique- 
fied Ammonia  at  once 
commences  evaporating 
back  from  the  receiver 
by  the  syphon-tube  and 

Ice  Machine.     First  Process.  yalye  g  jnto  ^  genera. 

tor,  where  it  is  immediately  absorbed  by  the  water  from  which 

it  had  been  previously  expelled. 

Fig.  97*.  This  rapid  evapora- 

tion produces  so  much 
cold  as  to  freeze  the 
water,  contained  in  the 
central  vessel  E,  solid  in 
the  course  of  l£  hours. 
By  this  evaporation  of 
the  liquefied  Ammonia 
back  into  the  genera- 
tor, the  liquid  which  it 
contains  is  restored  to 
its  original  strength,  and 
may  be  used  again  and 
again  for  the  production 
of  the  liquefied  gas. 
As  a  portion  of  the 

Carre's  Ice  Machine.     Second  Proems.  water,    about    ^tll,    dis- 

tills  over  with  the  gaseous  Ammonia  when  it  passes  from  the  gen- 
erator to  the  receiver,  from  which  it  does  not  all  return,  when 


206  AMOUNT    OF    ICE    PRODUCED. 

the  liquefied  Ammonia  evaporates  back  into  the  generator,  the 
receiver  becomes  gradually  filled  with  water,  arid  the  quantity 
contained  in  the  generator  becomes  correspondingly  diminished. 
To  obviate  this  difficulty,  in  machines  constructed  for  the  manu- 
facture of  ice  upon  a  large  scale,' the  receiver  is  placed  above 
the  generator,  that  the  water  may  be  drained  off  and  returned, 
charged  with  Ammonia,  to  the  generator  by  the  action  of  gravity, 
or  by  a  small  pump  worked  by  a  steam  engine. 

The  above  is  a  description  of  the  apparatus  as  first  invented 
and  used  upon  a  small  scale.  In  the  large  machines  intended 
for  the  manufacture  of  ice,  all  the  parts  are  greatly  enlarged 
and  strengthened.  The  generator  is  made  of  iron,  strongly 
hooped  with  steel  bands,  so  as  to  be  capable  of  sustaining  a 
pressure  of  700  Ibs.  to  the  square  inch.  A  large  tank  is  pro- 
vided for  the  reception  of  the  water  that  surrounds  the  receiver. 
The  receiver  consists  of  several  stacks  of  tubes,  and  these  are 

•  surrounded  by  a  solution  of  chloride  of  calcium,  a  liquid  which 
does  not  freeze  until  reduced  many  degrees  below  the  freezing 
point  of  water,  and  which  therefore  remains  permanently  liquid. 
In  this  solution  and  between  the  tubes  of  the  receiver  into  which 
the  liquefied  gas  evaporates,  are  placed  the  cans,  24  in  number, 

i filled  with  the  water  to  be  frozen.  As  the  liquefied  Ammonia 
evaporates,  into  the  tubes  of  the  receiver,  so  much  heat  is  ab- 
sorbed and  rendered  latent  that  the  temperature  of  the  solution 

.of  chloride  of  calcium  in  which  the  cans  are  immersed  is  speedily 
reduced  many  degrees  below  the  freezing  point  of  water,  32°F., 
and,  as  a  result,  the  water  contained  in  the  cans  at  the  expira- 
tion of  four  hours  is  completely  frozen.  The  cans  are  dipped 
for  a  moment  in  hot  water,  and  then  inverted,  in  order 
to  remove  the  ice.  The  blocks  of  ice  are  uniformly  rect- 
angular, and  as  their  temperature  is  far  below  32°,  by  simply 
moistening  their  surfaces  they  freeze  perfectly  to  each  other, 
and  form  solid  blocks  of  any  required  dimensions.  The  water 
introduce  1  into  the  cans  is  perfectly  pure,  being  obtained 
by  distillation  from  the  water  contained  in  the  boiler  of 
the  steam  engine.  The  ice  therefore  is  perfectly  pure,  is  very 
hard  and  compact,  and  is  much  longer  in  melting  than  natural 

How  is  the  water  which  goes  over  into  tho  receiver  returned  to  the  generator?  De 
scribe  the  arrangement  of  Carre's  Ice  machine  for  actual  use  upon  a  large  scale  for  the 
manufacture  of  ice.  Why  is  a  solution  of  chloride  of  calcium  employed  ?  How  is  the 
Ice  extracted  from  the  cans  in  which  it  is  frozen?  How  are  large  solid  blocks  formed  ? 
State  the  amount  of  ice  that  may  be  produce!  by  these  machines.  State  the  cost  per 
'pound. 


PRESSURE    EXERTED    BY    THE    LIQUEFIED    GASES.       207 

ice.  The  ice  can  also  be  made  at  a  very  small  expense.  At 
the  Louisiana  ice  works,  in  New  Orleans,  six  machines  produce 
from  72  to  76  tons  of  solid  ice  every  24  hours,  at  an  expense  of 
$3  per  ton.  It  is  estimated  that  about  eight  pounds  of  ice  may 
be  produced  for  one  cent.  At  this  cost,  one-half  cent  per  pound 
for  the  ice  would  yield  a  large  profit.  The  ice  made  by  this 
process,  under  the  direction  of  M.  Bujac,  is  used  by  seven- 
eighths  of  the  population  of  New  Orleans,  and  is  also  extensively 
exported  to  Mexico  and  Texas.  Millions  of  pounds  have  been 
manufactured  and  consumed.  It  is  evident  that  this  process  is 
possessed  of  very  great  value  to  the  inhabitants  of  all  hot 
climates,  not  simply  for  the  manufacture  of  ice,  but  for  the 
cooling  of  the  air  of  apartments  and  of  refrigerators. 

227.  Pressure  exerted  by  liquefied  Gases.  In  order  to 
estimate  the  pressure  which  the  condensed  gases  exerted  upon  the 
interior  of  the  tubes  in  which  they  were  contained,  and  to  de- 
termine the  force  requisite  to  overcome  the  repulsive  energy  of 
their  own  particles  in  the  gaseous  state,  small  air  gauges  were 
enclosed  in  the  condensing  tubes.  The  pressure  was  estimated 
by  the  degree  to  which  the  air  in  the  gauges  was  compressed. 
Many  of  the  liquefied  gases  expand  upon  the  application  of 
heat  more  rapidly  than  in  the  gaseous  state.  It  has  also  been 
found  that  Marriotte's  law,  that  the  elasticity  of  a  gas  increases 
directly  with  the  pressure,  although  correct  for  pressures  at  a 
considerable  distance  above  the  point  of  condensation,  does  not 
hold  good  as  this  point  is  approached ;  in  this  case  the  elasticity 
is  not  proportioned  to  the  pressure,  but  is  considerably  less  ;  be- 
cause the  repulsion  between  the  particles,  owing  to  the  diminu- 
tion of  distance,  is  no  longer  able  to  overcome  the  attraction  of 
cohesion,  this  attraction  increasing  in  power  the  more  nearly 
the  point  of  condensation  is  approached.  These  experiments 
have  been  prosecuted  with  great  success  by  Cagniard  de  la  Tour. 
Various  liquids,  such  as  water,  alcohol,  and  ether,  were  enclosed 
in  strong  glass  tubes,  hermetically  sealed,  so  as  to  fill  somewhat 
less  than  one-fourth  their  capacity.  These  were  then  cautiously 
heated ;  the  liquids  expanded  until  their  bulk  was  nearly 
doubled  ;  expansion  then  ceased,  in  consequence  of  the  immense 
pressure  to  which  they  were  subjected,  and  then  as  the  heat 
was  increased,  they  suddenly  passed  into  the  state  of  vapor  and 
disappeared.  Water  was  found  to  become  gaseous  in  a  space 

Name  the  gases  which  have  resisted  all  attempts  at  solidification.— 227  How  is  the 
pressure  in  the  interior  of  tubes  in  which  gases  are  condensed  estimated?  At  what  rate 
do  the  liquefied  gases  expand  ?  Describe  the  experiments  of  De  la  Tour. 


208    THE  CONSTITUTION  OF  THE  GLOBE  DEPENDS  ON 

equal  to  about  four  times  its  original  bulk,  at  a  temperature  of 
about  773°  F.,  that  of  melting  zinc.  As  the  vapors  cooled, 
suddenly  a  sort  of  cloud  filled  the  tube,  and  in  a  few  moments 
after,  the  liquid  reappeared.  Space  must  be  allowed  for  the 
full  expansion  of  the  liquid,  otherwise  the  strongest  vessels  will 
give  way.  Thus  it  has  been  ascertained,  from  these  and  other 
experiments,  that  there  exists  for  every  liquid  a  temperature  at 
which  no  amount  of  pressure  will  retain  it  in  the  liquid  state, 
but  it  will  inevitably  assume  the  form  of  a  gas.  This  being 
true,  it  is  not  strange  that  for  some  gases  there  is  a  temperature 
above  which  no  amount  of  pressure  is  sufficient  to  reduce  them 
to  the  liquid  state.  These  are  the  gases  which,  like  air  and 
oxygen,  have  remained  uncondensed,  whatever  the  pressure  to 
which  they  have  been  subjected. 

228.  The  present  constitution  of  the  Globe  entirely  depend- 
ent on  its  temperature.  From  these  and  other  experiments,  we 
justly  conclude  that  the  state  of  matter,  as  solid,  liquid,  or 
gaseous,  depends  chiefly  on  the  temperature  to  which  it  is  sub- 
jected. At  a  sufficiently  high  temperature,  the  most  infusible 
forms  of  matter,  such  as  refractory  minerals,  and  the  metal 
platinum,  would  naturally  exist  in  a  state  of  vapor,  as  aeriform 
fli'ds,  perhaps,  colorless,  inodorous,  and  invisible.  And  at  a 
former  period  in  the  history  of  our  planet,  it  is,  chemically 
speaking,  not  impossible  that  all  the  matter  of  which  the  earth 
consists  may  have  been  in  an  invisible  and  aeriform  state,  or 
perhaps  a  nebulous  mass.  On  the  other  hand,  at  a  sufficiently 
low  temperature,  probably  the  most  volatile  of  substances,  like 
the  atmosphere  and  oxygen  and  hydrogen  gases,  would  eventu- 
ally become  as  solid  as  the  most  solid  rocks  and  metals,  and  all 
the  aeriform  fluids  be  condensed.  In  such  a  state  of  things 
there  would  be  no  atmosphere  and  no  water,  nor  any  other  sub- 
stanee  on  the  face  of  the  whole  earth,  whose  particles  would 
possess  any  power  of  movement  among  themselves.  Either  of 
these  extreme  temperatures  would  be  fatal  to  the  existence  of 
man  and  animals,  as  well  as  to  that  of  plants,  and  strip  the 
earth  of  everything  pleasant  to  the  eye,  as  well  as  of  all  articles 
good  for  food.  That  neither  of  these  extremes  exists,  but  ex- 
actly that  happy  mean  in  virtue  of  which  all  the  three  states  of 
matter  can  exist  and  co-exist  side  by  side,  the  solid  rock,  the 
liquid  water,  the  gaseous  atmosphere,  is  surely  a  conspicuous 
proof  of  most  refined  design  in  the  arrangement  of  the  realm 

228.  Show  that  the  present  constitution  of  the  globe  is  entirely  dependent  upon  its 
temperature. 


I        ,  ITS    TEMPERATURE. EXPEHIMENTS.       "  209 

of  Nature,  and  a  sure  proof  to  us  of  the  goodness  and  the 
beneficence,  as  well  as  of  the  wisdom  and  power  of  the  Creator. 

Experiments :— Effects  of  Heat:    Evaporation, 

1.  Evaporation.    Heat  Is  absorbed  in  the  process  of  evaporation,  as  well  as  that 
of  ebullition.     This  may  be  shown  by  dropping  ether  upon  the  bulb  of  a  thermometer : 
the  mercury  falls,  because  its  heat  is  absorbed  by  the  vaporization  of  the  ether. 

2.  The  rapidity  of  evaporation  is  greatly  increased  by  the  removal  of  the  atmospheric 
pressure.     Place  ether  under  the  receiver  of  the  air  pump,  and  exhaust  the  air :  the 
ether  begins  to  boil,  and  a  thermometer  introduced  into  jt  sinks  below  82o. 

3.  Pour  ether  upon  the  surface  of  water  in  a  watch  glass,  and  evaporate  rapidly  by 
means  of  the  air  pump  :  the  water  will  be  frozen.     The  watch  glass  should  be  placed  in 
the  interior  of  a  large  vessel,  also  filled  with  ether.     To  make  these  experiments  succeed 
with  promptness  the  water,  ether,  and  sulphuric  acid,  as  well  as  the  vessels  employed, 
should  be  previously  cooled  by  being  placed  on  ice.     The  watch  glass  should  be  supported 
upon  a  ring  of  tin.  wound  with  woolen  cloth. 

4.  Place  water  in  a  watch  glass,  in  strong  sulphuric  acid,  and  exhaust  the  air  by  an 
air  pump.     The  water  will  be  frozen  by  its  own  evaporation.     The  vapor,  as  fast  as  it 
rises,  is  condensed  by  the  sulphuric  acid.     The  air  pump  must  be  kept  very  steady. 

5.  A  single  drop  of  water  placed  on  the  plate  of  an  air  pump  may  be  frozen  simply  by 
its  own  evaporation  ;  also  a  single  drop  of  water  placed  upon  a  piece  of  burnt  cork,  hol- 
lowed upon  its  upper  surface. 

6.  Provide  an  unbaked  clay  cup, — one  of  the  cups  of  Grove's  battery  will  answer  very 
well, — pour  water  into  it,  and  introduce  a  thermometer      As  the  water  percolates  through 
the  cup  and  evaporates,  the  thermometer  sinks.     The  effect  is  greater  if  ether  or  alcohol 
are  used. 

7.  Drop  ether  or  alcohol  upon  the  bulb  of  the  large  air  thermometer,  previously  de- 
scribed, Fig  45,  and  the  sinking  of  the  liquid  in  the  stem  will  be  very  marked. 

8.  Place  deep  wine  glasses  of  water,  alcohol,  and  ether,  under  the  same  receiver  of  an 
air  pump,  with  a  thermometer  in  each,  and  note  the  difference  in  the  cold  produced  when 
the  air  is  withdrawn,  owing  to  the  difference  in  the  rate  of  evaporation. 

9.  If  ether  be  allowed  to  fall,  drop  by  drop,  upon  a  thin  vial  of  water,  covered  with 
muslin,  in  a  current  of  air  like  that  produced  by  a  bellows,  the  water  will  be  fiozen. 

10.  That  heat  is  absorbed  by  evaporation,  under  all  circumstances,  is  shown  by  the 
cryophorus  of  Dr.  Wollaston.     The  empty  bulb  must  be  placed  in  a  freezing  mixture  of 
equal  parts  of  snow  and  salt ;  the  vapor  within  it  is  condensed  ;  rapid  evaporation  takes 
place  from  the  liquid  in  the  other  bulb,  and  it  soon  freezes.     Eoth  bulbs  should  be  pro- 
tected from  draughts  of  air,  and  previously  somewhat  cooled ;  the  experiment  should 
not  be  attempted  in  a  warm  room. 

1 1.  The  pulse  glass  held  in  the  hand,  as  soon  as  it  boils,  produces  a  sensation  of  cold, 
on  the  same  principle. 

12.  The  water  hammer,  made  to  boil  in  the  same  way,  also  illustrates  the  same  truth. 

13.  That  the  amount  of  moisture  existing  invisibly  in  the  air  depends  upon  its  tem- 
perature, may  be  shown  by  placing  a  bottle  of  moist  air,  tightly  corked,  upon  ice  and 
salt,  in  a  bowl.    As  the  air  cools,  a  cloud  appears  within  the  bottle, 

14.  Ice  and  snow  mixed,  and  placed  in  a  jar,  will  soon  induce  a  deposit  of  moisture 
on  the  outside,  from  the  air,  which  is  cooled  by  contact  with  it. 

15.  The  Dutch  weather  house;  the  sponge  balance  hygrometer;  the  hygrometer  of 
Saussure,  may  all  be  used  to  demonstrate  the  varying  amount  of  moisture  in  the  air,  by 
removing  them  from  a  damp  to  a  dry  atmosphere,  and  the  reverse. 

16.  Daniell's  hygrometer  will  illustrate  the  same  fact  on  a  different  principle. 

17.  Place  a  square  piece  of  copper  upon  the  surface  of  a  mixture  of  ice  and  salt,  and 
observe  the  minute  drops  of  moisture  formed.     This  illustrates  the  mode  in  which  dew 
is  formed  upon  the  earth,  the  difference  being  that  in  one  case  the  copper  is  cooled  by 
the  ice,  in  the  other  the  earth  is  cooled  by  radiation. 

18.  Expose  different  plates  of  different  substances,  such  as  glass,  wood,  rough  copper, 
polished  copper,  all  of  the  same  size,  on  a  cool  night  in  summer,  and  observe  the  different 
amounts  of  dew  collected  upon  them. 

19.  Place  a  thermometer  upon  the  ground  on  a  clear  night,  suspend  a  second  ther- 
mometer 10  or  12  feet  above  it,  in  the  air.  and  note  how  much  lower  the  first  sinks  than 
the  second,  showing  that  dew  is  caused  by  the  radiation  of  the  heat  of  the  earth,  and  not 
by  the  general  coolness  of  the  atmosphere. 

20.  Solidified  Carbonic  Acid.     The  dry  solid  acid  may  be  held  in  the  hand 
with  impunity ;  mixed  with  sulphuric  ether,  it  is  dangerous  to  handle. 


210  SPECIFIC    HEAT. 

21.  Place  a  small  quantity  on  stout  plate  glass,  no  effect  takes  place  so  long  as  it  re- 
mains dry  ;  pour  ether  on  it  and  the  glass  is  broken  at  once  by  the  intense  cold  which  is 
produced. 

2<i.  Mix  the  solid  carbonic  acid  with  sulphuric  ether,  upon  the  surface  of  mercury  in 
a  wooden  bowl.  The  metal  will  almost  immediately  be  frozen 

2  j.  Place  a  medal  at  the  bottom  of  the  bowl,  and  an  impression  of  the  medal  will  be 
taken  iu  the  ihercury. 

24.  Introduce  a  mercurial  thermometer,  and  observe  the  rapid  fall  of  the  fluid  into 
the  bulb,  and  its  subsequent  congelation  and  great  contraction. 

25.  Introduce  a  spirit  thermometer,  and  note  the  difference  of  effect. 

28.  Throw  some  of  the  solid  acid  upon  cold  water. 
27.  Tiirow  some  of  it  upon  hot  water. 

23.  Place  some  of  it  at  the  bottom  of  a  jar  in  which  a  candle  is  burning,  and  observe 
the  going  out  of  the  flame. 

29.  Introduce  a  taper  into  such  ajar. 

30.  Throw  some  of  the  solidified  mercury  into  water:  the  mercury  melts,  but  the 
water  at  the  same  time  freezes.     This  is  an  excellent  illustration  of  the  absorption  of  boat 
always  attendant  upon  liquefaction. 

31.  Place  some  of  the  solid  carbonic  acid  and  ether  under  the  receiver  of  an  air  pump, 
with  »•  spirits  thermometer  graduated  very  low,  and  exhaust ;  note  the  extremely  low 
temperature  produced ;   — — 166°  F. 

3J.  Heat  a  silver  or  platinum  capsule  to  a  full  red  heat,  over  a  powerful  spirit  vapor 
or  gas  lamp  ;  throw  in  a  quantity  of  mixture  of  solid  carbonic  acid  and  ether;  introduce 
quickly  a  little  mercury  in  a  platinum  spoon  ;  the  ether  will  probably  take  fire  and  burn, 
but  notwithstanding,  the  mercury  will  be  frozen,  and  may  be  turned  out  a  solid  mass 
upon  the  table. 

33.  Treat  water  in.  the  same  manner ;  it  will  also  be  frozen. 


§  VI.— Specific  Heat:— Capacity  for  Heat. 

229.  The  amount  of  Heat  in  different  bodies  of  the  same 
temperature  unequal.— Specific  Heat.  It  has  been  seen  that,  in 
the  important  processes  of  liquefaction  and  vaporization,  a  large 
amount  of  heat  disappears  and  becomes  latent,  without  producing 
'the  smallest  effect  upon  the  temperature  of  the  solid  and  liquid 
in  question.  It  is  evident,  therefore,  that  heat  can  exist  in  a 
body  without  being  free  or  sensible.  Heat,  in  this  state,  is 
called  heat  of  composition,  because  it  has,  so  to  speak,  combined 
with  the  body  which  it  has  entered,  producing  a  compound  sub- 
stance which,  in  some  respects,  does  not  exhibit  all  the  proper- 
ties of  its  component  parts ;  and  as  it  is  one  of  the  characteris- 
tics of  chemical  combination  that  the  properties  of  the  elements 
are  never  displayed  in  the  compound  produced,  it  is  supposed 
that  some  such  union  has  taken  place  in  this  case  between  the 
heat  absorbed,  and  the  body  in  question.  The  heat  thus  ab- 
sorbed is  called  Latent  Heat.  It  has  also  been  seen  that  equal 
weights  of  different  bodies  of  the  same  temperature  do  not  con- 
tain the  same  amount  of  heat.  Thus  a  pound  of  ice  at  32°(§§ 

229.  What  is  meant  by  heat  of  composition?    By  latent  heat? 


SPECIFIC    HEA.T    DETERMINED  211 

141  and  142)may  have  140°  of  heat  added  to  it,  and  be  converted 
into  a  pound  of  water  without  having  its  temperature  elevated 
1°.  It  is  evident,  therefore,  that  the  pound  of  water  at  32°  must 
contain  at  least  140°  more  heat  than  the  pound  of  ice  of  the 
same  temperature.  The  same  is  true  of  a  pound  of  steam  at 
212°,  and  a  pound  of  water  at  2 12°  ;  the  former  contains  at  least 
1000°  more  heat  than  the  latter,  and  yet  they  are  both  of  the 
same  temperature.  It  is,  therefore,  a  general  truth,  that  equal 
weights  of  the  same  substance  contain  equal  quantities  of  heat, 
but  equal  weights  of  different  bodies,  at  the  same  temperature, 
contain  unequal  quantities  of  heat.  This  difference  in  bodies, 
in  regard  to  the  amount  of  heat  which  they  contain  at  the  same 
temperature,  was  described  by  Dr.  Black,  who  was  the  earliest 
experimenter  upon  this  subject,  by  the  term  capacity  for  heat, 
"  a  word  apparently  suggested  by  the  idea  that  the  heat  present 
in  any  substance  is  contained  within  its  pores,  or  in  the  spaces 
left  between  its  particles,  and  that  the  quantity  of  heat  is  regu- 
lated by  the  size  of  its  pores."  This  term  is  now  discarded, 
and  in  place  of  it  that  of  specific  heat  has  been  generally  sub- 
stituted. Every  substance  is  said  to -have  a  specific  heat,  pecu- 
liar to  itself.  By  specific  heat  is  meant,  the  quantity  of  heat 
required  to  raise  the  temperature  of  any  given  substance  1°  F., 
compared  with  the  quantity  of  heat  required  to  raise  the  tem- 
perature of  an  equal  weight  of  water  1°.  The  specific  heat 
of  water  is  taken  as  unity,  and  that  of  all  other  bodies  is  differ- 
ent from  it,  because  an  equal  weight  of  each  requires  more  or 
less  heat  than  water  to  raise  its  temperature  1°.  The  spe- 
cific heat  of  water  being  1,  that  of  mercury  is  .033,  because  it 
requires  33  times  less  heat  to  raise  the  temperature  of  mercury 
1°,  than  it  does  to  raise  the  temperature  of  an  equal  weight 
of  water  1°.  The  specific  heat  of  bodies  is  one  of  their 
most  important  properties,  and  a  vast  amount  of  labor  and  skill 
has  been  expended  upon  the  different  methods  for  ascertaining 
it.  It  is  sometimes  called  calorimetry,  and  the  instruments  for 
determining  it  calorimeters. 

230.  Proof  that  equal  weights  of  different  substances  con- 
tain unequal  amounts  of  heat.— Specific  heat  determined  by 
mixture.  That  equal  weights  of  different  bodies  at  the  Fame 
temperature  contain  unequal  quantities  of  heat,  may  readily  be 

How  can  it  be  proved  that  equal  weights  of  different  bodies,  at  the  same  temperature, 
cont:iiu  unequal  amounts  of  heat  ?  What  is  meant  by  the  term  capacity  for  heat '.  What 
term  is  now  substituted  for  it?  What  is  meant  by  specific  heat  ?  Give  the  specific  heat 
of  wat»r  and  mercury.  State  what  is  meant  by  this. — 230.  Prove  that  equal  weights  of 
different  substances  contain  unequal  amounts  of  heat  by  the  process  of  mixture. 


212  BY   MIXTURE, 

proved  by  observing  that  the  same  number  of  degrees  of  heat 
communicated  to  two  different  bodies,  will  raise  their  tempera- 
tures very  unequally.  Thus,  if  to  a  pound  of  water,  and  a 
pound  of  mercury,  at  the  same  temperature,  equal  amounts  of 
heat  be  added,  the  temperature  of  the  mercury  will  rise  33 
times  as  much  as  that  of  the  water.  In  other  words,  water 
requires  33  times  more  heat  than  an  equal  weight  of  mercury 
in  order  to  be  raised  to  the  same  temperature.  The  equal 
amounts  of  heat  may  be  added  to  the  different  substances  in 
several  modes.  Thus,  if  to  1  Ib.  of  mercury  at  40°,  1  Ib.  of 
water  at  100°  be  added,  the  temperature  of  the  mixture  will 
stand  at  98£°,  i  e.,  the  1  fj°  lost  by  the  water  has  heated  the  mer- 
cury 58£°.  While  on  the  other  hand,  if  to  1  Ib.  of  water  at  40°, 
1  Ib.  of  mercury  at  100°  be  added,  the  temperature  of  the  mix- 
ture will  be  only  41^°,  i.  e.,  the  58£°  lost  by  the  mercury  will 
have  heated  the  water  by  1|°.  The  amount  of  heat  added  in 
both  cases  to  the  colder  substance  has  been  the  same,  but  the 
effect  has  been  to  raise  the  temperature  of  the  cold  water  only 
1 1°,  while  the  temperature  of  the  mercury  has  actually  been 
increased  58£°.  Water, .  therefore,  has  a  greater  power  of 
holding  heat,  or,  as  it  is  called,  a  greater  capacity  for  heat,  com- 
pared with  mercury,  in  the  proportion  of  63  to  1,  nearly.  In 
the  same  way,  if  to  1  Ib.  of  water  at  50°,  1  Ib.  of  spermaceti 
oil  at  100°  be  added,  the  temperature  of  the  mixture  will  be 
66f  °,  i.  e.,  the  33|°  lost  by  the  oil,  has  heated  the  water  only 
16|°,  while  if  the  experiment  were  reversed,  the  water  being 
at  100°,  and  the  oil  at  50°,  it  would  be  found  that  the  oil  had 
gained  33^°,  and  the  water  lost  16|°,  whence  it  appears  that 
the  capacity  of  the  water  for  heat  is  twice  as  great  as  that  of 
spermaceti  oil,  and  consequently,  that  in  order  to  warm  a  cer- 
tain weight  of  water  to  the  same  degree  as  an  equal  weight  of 
oil  and  mercury,  twice  as  much  heat  must  be  given  to  the  water 
as  to  the  oil,  and  33  times  as  much  as  to  the  mercury. 

231.  Specific  heat  determined  by  the  different  times  re- 
quired to  heat  equal  weights  of  different  bodies  an  equal  num- 
ber of  decrees.  The  same  fact  may  also  be  proved  by  noting 
the  time  required  for  equal  weights  of  different  substance-!,  to 
be  heated  by  the  same  number  of  degrees.  Let  a  pound  of 
water,  of  oil,  and  of  mercury,  placed  in  three  separate  flasks,  be 
brought  severally  to  the  temperature  of  50°,  and  then  placed 
in  a  bath  of  warm  water  at  100°.  It  will  be  found  that  when 

231.     Prove  the  same  thing  by  the  different  times  required  to  heat  equal  weights  of 
different  bodies  by  an  equal  number  of  degrees, 


BY    RATE    OF    COOLING, 


213 


I  the  mercury  has  reached  the  temperature  of  80°,  the  oil  will 
stand  at  52°,  and  the  water  at  51°,  and  that  though  eventually 
they  all  reach  the  same  temperature,  the  water  takes  33  times 
longer  to  acquire  that  heat  than  the  mercury,  and  twice  as  long 
as  the  oil.  They  are  all,  however,  receiving  heat  at  the  same 
rate ;  and  the  only  explanation  which  can  be  given  of  the  fact 
is,  that  the  water  has  more  capacity  for  receiving  and  contain- 
ing heat  in  an  insensible  form  than  the  other  substances,  or  that 
its  constitution  is  such  that  it  requires  more  heat  in  order  to 
have  its  external  and  sensible  temperature  raised  to  the  same 
point. 

232-  Specific  heat  determined  by  the  rate  of  cooling:  an 
equal  number  cf  degrees.  Again,  on  heating  a  pound  of  water, 
oil  and  mercury,  each  to  212°,  in  separate  flasks,  and  immersing 
them  in  melting  ice,  which  always  stands  at  the  constant  tempera- 
ture of  32°,  it  will  be  found  that  the  times  required  for  each 
to  cool  through  50°,  or  any  other  equal  number  of  degrees,  will 
be  in  the  proportion  of  33  to  2  and  1.  The  water  will  be  33 
times  longer  in  cooling  than  the  mercury,  and  twice  as  long  as 
the  oil. 

Fig.  95. 

WATER.  OIL.  MERCURY. 


212 


212 


212 


Capacity  for  Htnt  of  Water,  Oil  and  Mercury. 


232.  Show  how  specific  heat  can  be  determined  by  the  rate  of  cooling. 


2H 


BY    THE    MELTING    OF    ICE. 


233.  Specific  heat  determined  by  the  quantity  of  ice 
melted  by  equal  weights  of  different  substances  in  cooling: 
from  212°  to  32°.  It  this  be  true,  it  is  quite  evident  that  when 
water  cools  a  certain  number  of  degrees,  it  must  give  out  33 
times  as  much  heat  as  mercury  in  cooling  an  equal  number  of 
degrees,  and  twice  as  much  as  oil.  The  amount  of  heat  given 
out  can  readily  be  estimated  by  measuring  the  amount  of  water 
produced  by  the  melting  of  ice  in  each  case.  Thus,  let  a  pound 
of  water,  a  pound  of  oil,  and  a  pound  of  mercury,  contained  in 
separate  flasks,  be  brought  to  the  temperature  of  212°,  by  im- 
mersion in  boiling  water,  and  then  be  surrounded  by  ice  in  fun- 
nels, placed  over  graduated  glass  jars,  as  in  Fig.  95,  and  the 
quantity  of  water  produced  in  the  cooling  of  the  three  flasks 
from  212°  to  32°,  be  carefully  measured;  it  will  be  found  to  be 
in  the  case  of  the  vessel  of  water,  33  times  as  much  as  that 
produced  by  the  cooling  of  mercury,  and  twice  as  much  as  in 
the  case  of  oil. 

234-  The  Calorimeter  of  Lavoisier  and  Laplace.  The 
celebrated  calorimeter  of  Lav  oisier  and  Laplace,  was  constructed 
on  this  principle ;  Fig.  96.  The  apparatus  consists  of  three 


Fig.  96. 


The  Calorimeter  of  Lavoisier  and  Laplace. 

concentric  vessels  of  sheet  brass,  arranged  one  within  the  other. 

233-  Show  how  specific  heat  can  be  determined  by  the  quantity  of  ice  melted  by  bodies 
in  cooling  from  212°  to  32°.— 234.  Describe  the  calorimcN'r  of  I>avoisier  and  Laplace. 
Describe  a  more  simple  mode  of  determining  the  same  thing  by  a  vessel  of  ice. 


CALORIMETER    OF    LAVOISIER    AND    LA    PLACE.  215 

In  the  inner  is  placed  the  substance  whose  specific  heat  is  to  be 
determined,  having  been  previously  heated  to  212°  by  im- 
mersion in  boiling  water.  The  two  exterior  compartments,  A 
and  B,  are  filled  with  pounded  ice ;  the  ice  of  the  compartment 
A,  is  intended  to  be  melted  by  the  hot  body,  M  ;  the  ice  in  the 
compartment  B,  is  intended  to  cut  off  the  radiant  heat  of  the 
external  air,  in  order  that  the  ice  melted  in  A  may  be  due  solely 
to  the  heat  proceeding  from  the  body  M.  Two  stop-cocks  are 
provided,  D  and  E,  for  the  purpose  of  drawing  off  the  water. 
The  hot  body  is  first  introduced,  and  covered  with  a  double  lid ; 
the  stop-cock  D  is  then  opened,  and  the  water  formed  allowed 
to  trickle  into  a  measuring  glass.  When  the  temperature  of 
the  hot  body  has  fallen  to  32°,  the  water  will  cease  running,  and 
the  amount  is  then  carefully  measured  and  compared  with 
that  produced  by  the  cooling  of  an  equal  weight  of  water  from 
212°  to  32°.  It  has  been  objected  to  this  instrument,  that  a 
portion  of  the  water  formed  is  detained  by  adhesion  within  the 
inner  vessel,  and  that  a  portion  may  be 
?•  97.  frozen  a  second  time,  and  thus  the  indica- 

tions of  the  instrument  may  be  vitiated.  A 
more  simple  mode  of  determining  specific 
heat  is  to  place  the  body  previously  heated 
to  212°,  in  a  piece  of  ice  which  has  been 
scooped  out  to  receive  it  a  Fig.  97, 
and  covered  with  a  lid,  b,  of  the  same  mate- 

rial.     When  the  substance  has  cooled  to 

Specific  Heat.  32°,  the  water  should  be  poured  out  and 

measured  ;  this  amount  compared  with  that 
produced  by  an  equal  weight  of  water  in  cooling  from  212°  to 
32°,  will  give  the  specific  heat  required. 

235.  Specific  heat  determined  by  the  rise  of  temperature 
produced  by  the  immersion  of  equal  •weights  of  different 
bodies,  for  the  same  time  in  equal  weights  of  water.  In  this 
process,  equal  weights  of  water  and  of  the  substances  in  question 
are  heated  to  212°,  and  then  immersed  for  the  same  length  of 
time,  in  equal  weights  of  water,  of  exactly  the  same  tempera- 
ture. The  difference  in  the  temperature  of  the  water,  contained 
in  the  different  vessels,  will  give  the  specific  heat.  The  differ- 
ence in  the  time  required  for  heating  the  water  in  each  vessel 
an  equal  number  of  degrees  by  the  different  substances,  will  give 
the  same  result. 

23o.  Show  how  specific  heat  may  be  determined  by  the  number  of  degrees  of  heat  im- 
parted to  water  in  the  same  time. 


216 


SPECIFIC    HEAT    OF    SOLIDS 


236.  The  specific  heat  of  Water.     The   specific   heat   of 
water,  or  the  capacity  of  this  substance  for  heat,  is  greater  than 
that  of  any  other  liquid,  and  also  of  all  solids,  and  consequently 
to  change  the  temperature  of  large  masses  of  water,  is  a  work  of 
time.     Water  may  have  a  very  large  amount  of  heat  poured 
into  it  without  any  perceptible  effect  upon  its  temperature.     And 
on  the  other  hand,  a  vast  amount  of  heat  may  be  abstracted 
from  water  without  any  sensible  diminution  of  its  temperature. 
This  is  due  to  its  immense  capacity  for  heat.     Water,  therefore, 
in  consequence  of  the  slight  effect  produced  upon  it  by  varia- 
tions of  atmospheric  temperature,  would  make  a  very  poor  ther- 
mometric  fluid.     Mercury,  on  the  contrary,  whose  specific  heat, 
or  capacity  for  heat,  is  33  times  less  than  that  of  water,  yields 
to  the  slightest  change  of  temperature,  and  is  therefore  admira- 
bly adapted  to  thermometric  purpose*.     The  susceptibility  of 
bodies  to  changes  of  temperature  is  always  in  the  inverse  pro- 
portion to  their  specific  heat. 

237.  Specific  Heat  of  Solids.     The  determination  of  the 
specific  heat  of  bodies  is  necessarily  attended  with  great  diffi- 
culty, owing  to  the  variety  of  the  sources  of  error,  and  the  num- 
ber of  precautions  required;   and  much  careful  consideration 
and  experiment  has  been  bestowed  upon  it.     The  following 
table  gives  some  of  the  results  of  M.  Regnault,  one  of  the 
most  successful  of  the  later  experimenters  on  this  subject,  ob 
tained  by  the  processes  of  immersion  and  mixture,  and  they 
bring  to  light  some  very  curious  facts : 

Specific  Heat  of  Solids  of  equal  weight  between  32°  and  212°. 


Water, 1. 

Charcoal, 0.24150 

Glass,      ......  0.19768 

Iron, 0.11879 

Zinc, 0.09555 

Copper, 0.09515 

Brass, 0.09391 


Silver, 0.05701 

Tin, 0.05623 

Mercury, 0.03332 

Platinum, 0.03243 

Gold, 0.03244 

Lead,  ,  0.03140 


238.  Specific  heat  of  Liquids.  The  specific  heat  of  liquids 
is  determined  by  the  same  methods  as  that  of  solids.  Water  is 
taken  as  the  standard,  and  the  specific  heat  of  all  other  liquids 
is  compared  with  it.  The  specific  heat  of  water  is  greater  than 
that  of  all  other  liquids,  without  exception.  A  body  in  the 

233  How  does  the  specific  heat  of  water  compare  with  that  of  other  bodies  ?  What 
are  some  of  the  results  of  this  peculiarity  ? — 237.  Give  som«  of  the  results  of  Regnault's 
table.— 238.  How  is  the  specific  heat  of- liquids  determined?  Give  the  table. 


AND    LIQUIDS.  217 

liquid  state  has  a  higher  specific  heat  than  the  same  substance 
when  in  the  solid  form.  This  is  very  marked  in  the  case  of 
water,  in  which  the  specific  heat  is  double  that  of  ice,  water 
being  1.000,  ice  is  0.505. 

Table  of  Specific  Heat  of  Liquids. 


Water, 1.00000 

Oil  of  Turpentine,    .     .  0.42593 

Alcohol, 0.615 

Ether,  ,  0.5113 


Bi-Sulphide  of  Carbon, 

Bromine,       

Chloroform, 


239.  Specific  heat  of  Gases.  The  determination  of  the  spe- 
cific heat  of  gases  is  attended  with  unusual  difficulties,  on  ac- 
count of  the  facility  with  which  their  bulk  and  weight  are  influ- 
enced by  external  circumstances,  and  though  conducted  by  many 
philosophers  of  distinguished  experimental  skill,  the  best  results 
can  be  viewed  only  as  approximations,  requiring  to  be  corrected 
by  future  research.  Dr.  Crawford,  the  first  careful  experimenter 
on  this  subject,  conducted  his  experiments  in  the  following  man- 
ner. He  selected  two  copper  vessels,  made  as  light  as  possible, 
and  exactly  of  the  same  form,  size  and  weight,  exhausted  one 
of  them,  and  filled  the  other  with  the  gas,  to  be  examined.  They 
were  heated  to  the  same  temperature  by  immersion  in  the  same 
vessel  of  hot  water,  and  then  plunged  into  equal  quantities  of 
cold  water,  of  the  same  temperature.  Each  flask  heated  the 
water ;  but  while  the  exhausted  flask  communicated  solely  the 
heat  of  the  copper,  the  other  gave  out  the  heat  of  the  copper 
plus  that  of  the  gas  which  it  contained.  The  number  of  de- 
grees by  which  the  cold  water  was  heated  by  the  former, 
deducted  from  the  number  of  degrees  by  which  it  was  heated 
by  the  latter,  gave  the  heating  power  of  the  confined  gas.  By 
repeating  the  experiment,  with  air  and  different  gases,  their 
comparative  heating  powers,  or  specific  heats,  were  ascertained. 
These  experiments,  though  correct  in  principle,  are  not  consid- 
ered reliable,  on  account  of  the  superior  heating  influence  of 
the  copper  globes  compared  with  the  small  amounts  of  gas  that 
were  employed.  The  same  subject  was  next  investigated  by 
Lavoisier  and  Laplace,  with  the  aid  of  their  calorimeter  ;  §  234. 
A  current  of  gas  was  transmitted  through  a  spiral  tube  placed  in 
boiling  water,  in  order  to  be  heated  to  a  fixed  temperature,  and 
was  then  made  to  circulate  within  the  calorimeter,  in  a  similar 

239.  How  is  the  specific  heat  of  gases  determined?    Describe  Crawford's  process.    De- 
scribe Lavoisier's  method. 


218 


SPECIFIC    HEAT    OF    GASES. 


tube,  surrounded  by  ice.  Its  temperature,  in  entering  and  quit- 
ting the  calorimeter,  was  noted  by  means  of  thermometers,  and 
the  number  of  degrees  of  heat  lost  in  cooling  from  212°  to  32° 
was  estimated  by  the  quantity  of  ice  liquefied.  These  experi- 
ments, though  very  ingenious,  and  conducted  with  great  care, 
are  thought  to  be  inaccurate,  for  the  reason  previously  given, 
that,  in  the  use  of  ice,  a  portion  of  the  water  formed  may  be 
frozen  a  second  time  in  consequence  of  the  low  temperature  of 
the  apparatus,  and  a  portion  also  detained  and  prevented  from 
escaping  into  the  measuring  glass,  by  the  adhesive  action  of  the 
ice.  A  similar  set  of  experiments  was  afterwards  undertaken 
by  Delaroche  and  Berard.  They  transmitted  known  quantities 
of  gas,  heated  to  212°.  in  a  uniform  current  through  the  calo- 
rimeter, and  instead  of  ice,  surrounded  the  serpentine  tube  with 
water.  The  temperature  of  the  gas,  at  the  moment  of  its  exit, 
was  carefully  noted,  and  the  number  of  degrees  of  heat  which 
it  imparted  to  the  water,  in  cooling  from  212°,  was  also  carefully 
ascertained  by  delicate  thermometers.  The  results  of  their 
experiments  are  contained  in  the  following  table,  which  for  a 
long  time  was  thought  to  furnish  the  most  accurate  determina- 
tion of  the  specific  heat  of  gases.  Equal  weights  of  the  gases 
were  used  in  all  cases.  In  the  first  column  the  specific  heat  of 
water  is  taken  as  the  standard  of  comparison ;  in  the  second 
column  the  specific  heat  of  air  is  taken  for  the  standard : 

Delaroche  and  Berartfs  Table  of  the  Specific  Heat  of  Gases.         -  jt 


Gases,  equal  weights. 

Water  the 
Standard. 

Air  the 
Standard. 

Water,     

1.0000 
0  8470 

/ 

Air,          

0.2669 

1  0000 

0.2361 

0.8848 

0.2754 

1  0318 

3  2936 

1°  3400 

Protoxide  of  Nitrogen,     .... 
Heavy  Garb.  Hydrogen,        .         .         , 

0.2369 
0.4207 
0  2884 

0.8878 
1.5763 
1  0805 

Carbonic  Acid,     ..... 

0.2210 

0.8280 

It  is  very  evident,  from  this  table,  that  equal  weights  of  the 
different  gases  differ  very  much  in  the  quantity  of  heat  which 
they  contain.  The  specific  heat  of  hydrogen  is  twelve  times 


Describe  that  of  Delaroche  and  Berard.  Give  some  of  the  results  of  their  table.  How 
does  the  specific  heat  of  hydrogen  compare  with  that  of  other  gases,  and  even  with  the 
metals. 


REGXAULT'S  TABLE. 


219 


greater  than  that  of  air ;  that  of  nitrogen  and  oxide  of  carbon 
about  the  same  as  air.  Compared  with  water,  the  specific  heat 
of  hydrogen  is  more  than  three  times  greater,  and  larger, than 
that  of  any  other  known  substance.  Out  of  nine  gases,  on 
which  experiments  were  made,  none,  except  hydrogen,  has  a 
specific  heat  equal  to  that  of  water ;  but  they  all  have  a  specific 
heat  much  greater  than  that  of  any  of  the  metals.  Thus  hydro- 
gen, the  lightest  known  substance,  has  the  greatest  specific  heat, 
while  the  metals,  the  heaviest  of  all  bodies,  possess  the  least. 

240.  Hegnaults  determination  of  the  specific  heat  of 
Gases.  Within  a  few  years  the  same  subject  has  been  investi- 
gated by  Regnault.  The  method  adopted  was,  in  the  first  place, 
to  condense  the  gas  in  a  strong  receiver ;  a  known  weight  was 
then  allowed  to  escape  at  a  perfectly  uniform  rate  through  a 
spiral  tube  plunged  into  a  vessel  of  hot  oil,  which  was  main- 
tained at  a  fixed  temperature ;  the  gas  was  in  this  way,  during 
its  passage  through  the  spiral,  raised  to  a  known  temperature 
equal  to  that  of  the  oil  in  the  bath ;  it  was  then  made  to  pass 
through  a  metallic  vessel,  surrounded  by  a  known  weight  of 
water ;  and  finally,  was  allowed  to  escape  slowly  into  the  air, 
ample  time  being  given  for  its  temperature  to  be  reduced  to 
that  of  the  surrounding  water.  By  this  process  the  rise  of 
temperature  experienced  by  a  known  weight  of  water  when  a 
given  weight  of  each  gas,  after  it  had  been  raised  to  a  fixed 
standard  temperature,  was  passed  through  it,  was  ascertained. 
The  different  gases  treated  in  this  way,  were  found  to  impart 
unequal  quantities  of  heat  to  the  water,  and  this  became  a 
measure  of  their  specific  heat.  The  results  are  given  in  the 
following  table : 

Regnault n  Table  of  the  Specific  Heat  of  Gases. 


Gases,  equal  weights. 

Water  the 
Standard. 

Water,    ....... 
Watery  Vapor,           ..... 
Air,         ..,.,.. 

Oxygen,    j    •  ,             „ 
Nitrogen,  '\        - 
Hydrogen,  '  .             .             ,             f 
Protoxide  of  Nitrogen,                » 
Heavy  Carb.  Hydrogen,         .             „             .             . 
Oxide  of  Carbon,             ..... 
Carbonic  Acid,           ..... 

1.0000 
0.4750 
0.2377 
0.2182 
0.2440 
3.4046 
0.2238 
0.3694 
0.2479 
0.3308 

^s 

240.  Describe  Regnault's  process.     Give  some  of  the  results  of  his  table. 


220  SPECIFIC    HEAT    AFFECTED    BT 

On  comparing  this  table  with  that  of  Delaroche  and  Berard, 
considerable  diversity  is  found,  but  not  more  than  might  be  ex- 
pected from  the  improved  methods  of  experimentation  that  have 
been  introduced  since  their  time.  The  important  fact  is  proved 
by  both  tables,  that  equal  weights  of  different  gases  of  the  same 
temperature,  and  the  same  density,  contain  very  unequal  amounts 
of  heat,  and  that  there  is,  therefore,  no  relation  between  the 
thermometric  temperature  of  a  body  and  the  actual  amount  of 
heat  which  it  contains ;  also  that  the  specific  heat  of  hydrogen, 
the  lightest  substance  known,  is  not  only  greater  than  that  of 
all  the  gases,  but  actually  nearly  3£  times  greater  than  that  of  an 
equal  weight  of  water  of  the  same  temperature ;  and  as  the 
specific  heat  of  water  is  superior  to  that  of  every  other  liquid  and 
solid,  it  follows  that  the  specific  heat  of  hydrogen  is  greater  than 
that  of  any  other  known  substance. 

211.  The  specific  heat  of  a  body  may  be  changed  by  alter- 
ing:  its  density.  The  specific  heat  of  a  body  is  not  a  per- 
manent property,  but  may  be  altered  by  changing  its  density. 
Any  influence  which  alters  the  distance  between  the  particles 
of  a  body,  affects  its  specific  heat.  If  the  particles  be  brought 
nearer  to  each  other,  specific  heat  is  diminished ;  if  the  parti- 
cles be  separated  and  removed  to  a  greater  distance  from  each 
other,  the  specific  heat  of  the  body  is  increased.  If,  by  mechani- 
cal compression,  the  particles  of  a  piece  of  soft,  well  annealed 
copper,  whose  specific  heat  varied  from  0.09501  to  0.09455,  be 
brought  nearer  to  each  other,  the  specific  heat  will  be  found  to 
ba  reduced  from  0.093 6  to  0.0933;  on  being  again  thoroughly 
annealed,  so  as  to  recover  its  former  density,  its  specific  heat 
will  be  nearly  restored  to  what  it  was  before, — 0.09493  to  0.09479. 
When  water,  or  any  other  liquid,  is  compressed,  its  specific  heat 
is  diminished ;  when  it  is  allowed  to  expand  to  its  former  dimen- 
sions, its  specific  heat  returns  to  the  same  amount  as  before. 
The  same  is  true  of  gases ;  if  they  are  compressed,  their  specific 
heat  is  diminished ;  but  if  allowed  to  expand,  their  specific  heat 
is  greatly  increased.  Regnault  denies  this  in  the  case  of  the 
gases,  but  his  conclusions  are  in  direct  opposition  to  those  of 
Delaroche  and  Berard,  and  nearly  all  other  experimenters,  and 
they  must,  therefore,  be  received  with  some  hesitation.  As  the 
distance  between  the  particles  of  bodies  is  very  much  affected 
by  change  of  temperature,  a  removal  of  the  particles  from  each 

241.  What  effect  is  produced  upon  the  specific  heat  of  bodies  by  altering  their  den- 
sity ?  Give  illustrations.  What  effect  is  produced  upon  specific  keut  by  elevation  of 
temperature  ?  Give  the  table. 


CHANGE    OF   DENSITY    OR    STATE. 


221 


other,  and  expans:on  being  produced  by  a  rise,  while  contraction 
is  the  result  of  a  diminution  of  temperature,  it  follows  that  the 
specific  heat  of  a  body  is  greater  at  a  high  temperature,  than  at 
a  low  one.  This  is  true  of  Folids,  liquids,  and  gases.  In  the 
ca.°e  of  gases,  it  is  denied  by  Regnault ;  but  the  correctness  of 
his  opinion  may  be  doubted.  That  it  is  true  of  soLds,  may  be 
plainly  seen  from  the  following  table : 

of  Specific  Heat  with  rise  of  Temperature. 


Specific  Heat 
from  32°  to  212°. 

Specific  Heat 
from  320  to  5720. 

0.0330 

0.0350 

Platinum,      

6.0886 

0.0355 

Antimony,        ...... 
Silver,     '      
Zinc,         
Cooper, 

0.0507 
0.0557 
0.0927 
0.0949 

0.0549 
0.0611 
O.KH5 
0.1013 

Iron,         ....... 

0.1098 

0.1218 

Glass,   

0.1770 

0.1900 

242-  The  specific  heat  cf  a  body  changed  by  altering1  its 
physical  state.  A  body  in  the  liquid  state  has  a  higher  specific 
heat  than  the  same  substance  when  in  the  state  of  a  solid.  On 
the  other  hand,  a  substance  in  the  gaseous  state  has  a  lower 
specific  heat  than  the  same  substance  in  the  liquid  state.  When 
ice  passes  into  the  liquid  state,  its  specific  heat  is  doubled ;  but 
when  water  is  converted  into  vapor,  its  specific  heat  is  dimin- 
ished one  half.  Different  solids  have  the  amount  of  their  spe- 
cific heat  differently  affected  by  a  change  of  state,  and  they  vary 
very  much  among  themselves. 

2-S.3.  A  chang-c  in  the  specific  heat  of  a  body  always  chang- 
es its  temperature !  an  increase  of  specific  heat  diminishes  tem- 
perature, and  a  diminution  cf  specific  heat  increases  it-  Change 
of  Density,  or  of  the  State  of  bodies,  always  produces  change 
of  temperature-  It  has  been  shown,  in  the  case  of  soft  copper, 
that  a  change  in  the  specific  heat  of  a  body  is  always  produced 
when  a  change  is  made  in  its  density  ;  if  its  density  be  increa  ed, 
its  specific  heat  is  diminished ;  if  its  density  be  diminished,  its 
specific  heat  is  increased.  Besides  this  effect,  and  as  a  conse- 
quence of  it,  a  change  in  the  temperature  of  the  body  whose 
density  is  altered,  is  always  produced.  In  the  ca?e  of  soft  cop- 
per, if  density  be  increased,  and  specific  heat  diminished,  tem- 
perature rises ;  if  density  be  diminished,  and  specific  heat  be 

^42,  What  effect  is  produced  upon  specific  heat  by  change  of  state?— 243-  What  effect 
Jfl  produced  upon  temperature  by  change  of  specific  heat  ? 


222  CHANGE    OF    DENSITY 

increased,  temperature  sinks.  So  great  is  the  effect  upon  tem- 
p  'rature,  in  consequence  of  a  change  of  specific  heat,  produced 
by  a  change  in  density,  that  if  a  piece  of  iron  be  rapidly  ham- 
mered it  immediately  becomes  hot,  and  by  a  skillful  blacksmith, 
may  even  be  made  red-hot  by  this  process.  This  rise  in 
temperature  may  be  thus  explained.  The  distance  of  the 
particles  of  bodies  from  each  o;her  is  in  general  determined  by 
their  specific  heat.  This  specific  heat  spends  its  energy  in  keep- 
ing the  particles  apart,  and  in  resisting  the  attraction  of  cohesion 
which  is  constantly  tending  to  draw  them  together,  and  it  no 
longer  possesses  the  power  of  affecting  temperature.  When- 
ever heat  is  expended  in  producing  any  mechanical  effect  of 
this  kind,  it  loses  its  power  of  affecting  the  thermometer  and 
t'ie  senses,  and  passes  from  a  sensible  to  an  insensible  state. 
Heat  can  not  produce  an  effect  upon  temperature  and  a  me- 
chanical effect,  at  the  same  time.  A  definite  amount  of  heat 
m  ide  to  pass  into  a  body  may  cause  the  temperature  of  the 
body  to  rise,  or  it  may  spend  itself  in  increasing  the  distance 
between  its  particles,  and  expanding  it,  but  it  can  not  do  both  at 
the  same  moment.  Heat  which  has  caused  a  body  to  expand,  can 
not  at  the  same  time  rai-e  its  temperature.  When  a  piece  of 
ii-on  is  held  near  the  fire,  the  first  effect  of  the  heat  is  to  expand 
the  iron,  and  this  it  does  without  raising  its  temperature ;  this 
h?at  becomes  lafent  in  the  iron,  and  the  temperature  of  the 
body  does  not  ri  e  unless  it  receives  more  heat  from  the  fire 
than  can  be  employed  in  effecting  expansion.  But  the  heat  that 
has  been  expended  in  this  manner,  and  become  latent  in  any 
substance,  is  not  lo  t;  it  will  again  become  heat  of  temperature 
as  soon  as  it  is  no  longer  needed  for  the  purpose  of  keeping  the 
particles  of  the  body  apart.  If  mechanical  force  should  vio- 
lently compress  the  body  and  bring  the  particles  nearer  together, 
the  heat  which  had  previously  kept  them  apart  being  now  no 
longer  needed  for  this  purpose,  will  make  itself  apparent  as 
heat  of  temperature.  This  is  what  takes  place  when  cold  iron 
is  hammered ;  the  heat  which  had  kept  the  particles  asunder, 
and  which  had  remained  latent  while  thus  expended,  being  now 
no  longer  able  to  exert  this  effect,  is  compelled  to  appear  as 
heat  of  temperature,  and  the  iron  at  once  becomes  very  hot. 
If,  on  the  other  hand,  the  particles  of  iron  had  been  separated 
from  each  other  by  mechanical  violence,  they  could  not  have 

What  effect  is  produced  upon  temperature  by  the  compression  and  expansion  of  bodies^ 
Of  passing  from  the  solid  to  the  liquid  or  giseous  state  ?  Give  illustrations.  Explain 
toe  beating  of  iron  red-hot  by  hammering.  .From  what  source  is  this  heat  derived  ? 


AFFECTS    TEMPERATURE.  223 

remained  permanently  separated  except  by  the  agency  of  heat, 
for  which  there  would  be,  therefore,  an  imperative  demand. 
All  the  heat  in  the  neighborhood  would  be  drawn  upon  for  the 
purpose  of  satisfying  this  demand,  and  the  first  source  would  be 
the  free,  sensible  heat  of  the  body  itself.  This  would  at  once 
be  transferred  into  the  latent  state,  and  be  expended  in  main- 
taining the  distance  between  the  particles ;  it  would  cease, 
therefore,  to  appear  as  heat  of  temperature,  and  the  iron  would 
at  once  become  cold.  The  quantity  of  heat  latent  in  the  metals, 
and  which  becomes  apparent  when  they  are  compressed,  is  ad- 
mirably illustrated  by  the  faint  flash  of  light  which  is  emitted 
when  a  bullet  from  a  steam  gun  strikes  a  wrought  iron  target. 
The  bullets  are  completely  flattened,  and  when  directed  against 
a  plate  of  lead  placed  in  front  of  the  target,  the  two  surfaces  of 
lead  become  firmly  united  as  if  melted  or  soldered  together. 
The  fla-h  of  light  is  only  visible  in  a  darkened  room.  Another 
still  more  striking  illustration  is  seen  in  the  flash  of  light  pro- 
duced when  the  80  Ib.  hexagonal  bolts  fired  from  the  Whit- 
worth  gun  strike  the  thick  iron-plated  sides  of  a  floating  battery, 
Fig.  98.  "Notwithstanding  the  immense  resisting  power  of  the 

Fig.  98. 


• 

. 


The  Latent  Heat  of  Iron  Shot  and  Plates  rendered  Sensible  by  Compression. 

iron  plates,  the  hexagonal  bolt  passed  completely  through  them. 
The  shot  when  discovered  was  found  to  be  so  hot  that  no  one 

Explain  the  heat  and  light  produced  by  the  shot  from  the  Whitworth  guns,    Givf 
Ptber  illustrations, 


224  ILLUSTRATIONS. 

could  touch  it,  and  was  ascertained  to  have  been  compressed  to 
the  extent  of  an  inch  in  length.  It  was  noticed  that  at  the 
instant  of  concussion  between  the  shot  and  the  vessel,  a  broad 
S7ieet  of  intensely  bright  flame  was  emitted,  almost  as  if  a  gun 
hcid  been  fired  from,  the  vessel  in  reply"  The  same  effect  has 
been  repeatedly  noticed  when  the  balls  from  the  heavy  Dahlgren 
guns  of  the  Monitors  struck  the  stone  fortifications  against 
which  they  were  directed.  The  heat,  in  these  cases,  was  that 
previously  latent  in  the  iron,  made  sensible  by  the  compression 
of  the  metal  and  the  diminution  of  its  specific  heat.  In  like 
manner,  the  intense  heat  which  is  evolved  when  iron  bars  are 
subjected  to  the  process  of  rolling,  and  not  unfrequently  by  the 
axles  of  cars  and  carriages  when  in  rapid  motion,  and  in  the 
processes  of  boring  and  planing  metals,  is  due  to  the  same  cause. 
It  is  the  heat  previously  latent  in  the  metals,  evolved  and  con- 
verted into  heat  of  temperature  by  the  diminution  of  their  spe- 
cific heat  in  consequence  of  compression.  The  heat  set  free  in 
the  simple  operation  of  boring  a  hole  with  a  gimlet,  is  sufficient 
to  inflame  a  friction  match.  The  heat  produced  by  the  rapid 
drawing  of  a  string  tightly  around  the  ne^k  of  a  glass  flask,  is 
sufficient  to  crack  it.  And  in  the  whale  fishery,  the  heat  evol- 
ved by  the  inconceivably  rapid  motion  of  the  rope  over  the  side 
of  the  boat,  after  the  whale  is  struck,  would  be  sufficient  to  set 
it  on  fire  if  it  were  not  kept  cool  by  the  continual  pouring  of 
cold  water.  In  the  best  constructed  steam  engines,  the  bear- 
ings of  the  shafts  are  made  hollow,  and  a  steady  stream  of  cold 
water  caused  to  circulate  through  them,  in  order  to  prevent 
them  from  becoming  excessively  heated,  and  the  axles  from  ex- 
panding to  such  a  degree  as  to  be  incapable  of  moving.  These 
are  illustrations  of  a  general  principle.  Whenever  any  body  is 
expanded,  heat  is  absorbed  and  temperature  sinks.  Whenever 
any  body  is  compressed,  latent  heat  is  given  out  and  temperature 
rises.  This  is  true  of  solids,  liquid*,  and  gases.  Liquids,  if  com- 
pressed, grow  warm ;  if  relieved  from  compression,  they  grow 
cold  again.  Gases,  if  compressed,  grow  hot ;  if  released  from 
compression,  temperature  declines.  So,  in  like  manner,  when 
bodies  change  from  the  solid  to  the  liquid  or  gaseous  state,  there 
is  an  absorption  of  heat,  because  of  the  large  amount  which  is 
expended  in  making  the  change.  The  difference  between  the 

What  effect  is  produced  upon  temperature  of  the  passage  of  a  solid  into  the  1'quid  and 
gaseous  stite?  Of  the  passage  of  gases  and  liquids  into  the  solid  state?  When  :i  liquid 
is  vaporized,  what  effect  is  produced  upon  temperature?  What  when  a  yapor  is  coo« 
densed  into  a  liquid? 


i;    FIRE    SYKIMiK. 


225 


§amo  eubstancoiw  ft  solid  and  a<  a  liquid  is  that  in  the  lat'er 
ca.-e  the  particle-;  an-  o  far  removed  that,  they  can  slip  readily 
U|K>ii  each  o:her.  This  separation  can  only  be  inainlained  by 
the  addiiion  of  a  large  amount  of  heat.  Consequently,  when- 
ever a  solid  is  liquefied  there  is  an  immense  al>  orption  of  heat, 
and  temperature  sinks;  whenever  a.  liquid  is  solidified,  the  re- 
verse takes  place  and  temperature  rises.  The  latent  heat  no 
longer  required,  becomes  sensible.  When  a  liquid  is  \apoi  i/ed, 

heat  is  absorbed  and  temperature  sinks.  When  a  vapor  is  con- 
densed into  a  liquid,  latent  heat  is  given  out  and  temperature 
rises. 

244.    The  rire  Syringe.     Those  principle*   are   admirably 
illustrated  by  the  fire  syringe   represented  in  Fig.  99.      It  con- 
sists in  its  most  improved  Ibrm  of  a  hollow   cylinder  of  glass, 
into  which  a  piston  fits  air-tight.     Upon  the  under  side  of  the 
piston  is  a  cavity  to  receive,  a  bit  of  tinder  or  punk,  or  a  tuft  of 
cotlon  moistened  with  ether.      On    driving    the    piston    forcibly 
down,  the  tinder  will  emit    smoke,  and   finally  ignite:  a  match 
may    thus    be     lighted     with     ease.      This 
Fig.  99.  large  amount  of  heat  has   proceeded  from 

the  air  contained  in  the;  cvlinder.  By 
sudden  and  forcible  compression  its  den- 
sity is  increased,  its  particles  are  brought 
nearer  together,  the  heat  previously  ex- 
pended in  keeping  them  asunder  and  la- 
tent in  the,  air  is  made  sensible,  becomes 
heat  of  temperature,  and  is  sufficient  to 
inflame  the  tinder.  It  is  an  exj  eriment 
strictly  analogous  to  the  heating  iron  red 
hot  by  hammering.  On  rarefying  air  the 
opposite  effects  are  obsei  ved.  The  mist 
observed  in  the  receiver  of  an  air-pump 
wh'le  it  is  undergoing  exhaustion,  is  a 
proof'of  the  production  of  cold.  As  the 
air  is  withdrawn,  that  which  remains  un- 
dergoes ji  corresponding  rarefaction.  A 
demand  for  heat  is  created  to  sustain  this 
rarefied  stale.  A  large  amount  of  heat  be- 
comes latent,  and  temperature  sinks  SO 
low  that  the  ino'stiire  in  the  air  can  no 
ri,,-  Fin  Pump.  longer  remain  in  the  state  of  vapour,  but 

244.  Di'Bcribo  the  fire  Byrintfo.     Explain  its  principle. 


226  APPLICATIONS   OF 

is  condensed  in  minute  drops.  A  thermometer  placed  in  such 
a  receiver  rapidly  sinks  as  the  air  is  exhausted,  m  consequence 
of  the  rarefaction,  but  when  readmitted  it  rises  again  witn  equal 
rapidity,  in  consequence  of  the  condensation.  It' the  blast  fiom 
an  air  gnn  be  directed  upon  a  delicate  thermometer,  the  mer- 
cury will  sink  at  the  moment  of  discharge,  owing  to  the  enor- 
mous expansion  of  the  air.  And  when  steam  from  a  boiler  sud- 
denly issues,  under  great  pressure,  from  a  small  aperture  into 
the  atmosphere,  its  instantaneous  expansion  cools  it  to  such  a 
degree  that  instead  of  scalding  the  hand  held  in  it,  as  is  the 
case  with  ordinary  steam,  it  scarcely  feels  warm. 

245.  The  distribution  of  temperature  in  the  Atmosphere, 
the  formation  and  disappearance  of  clouds,  the  production  of 
rain  and  snow  explained  by  change  of  density  in  the  air.  These 
facts  explain  the  great  cold  of  the  atmosphere  of  the  earth  at 
high  elevations.  In  consequence  of  the  diminution  of  pressure 
at  high  altitudes,  the  air  is  much  more  rare  than  it  is  at  the  sur- 
face of  the  earth.  The  sensible  heat  of  temperature  which  it 
would  possess  if  it  were  everywhere  of  the  same  density  as 
it  is  at  the  surface  of  the  earth,  has  been  absorbed  in  conse- 
quence of  its  rarefaction,  and  is  now  latent.  The  higher  we  as- 
cend, the  greater  the  rarefaction,  and  consequently  the  greater 
the  absorption  of  heat,  and  the  lower  the  temperature.  The 
average  depression  of  temperature  is  about  1°  F.  for  every  300 
feet  of  ascent.  If,  therefore,  a  portion  of  air  from  the  surface 
of  the  earth  were  suddenly  carried  to  a  great  altitude,  its 
temperature  would  fall,  its  watery  vapor  be  condensed,  and 
clouds  be  produced,  §  202.  If  on  the  other  hand,  a  portion  of 
air,  at  a  great  elevation,  were  suddenly  brought  near  the  earth, 
its  temperature  would  be  greatly  elevated  in  consequence  of  its 
condensation,  and  if  it  contained  mists  and  clouds,  these  would 
disappear.  Change  of  place  among  portions  of  the  atmosphere 
is,  of  itself,  able  to  produce  great  changes  in  its  temperature, 
and  in  its  clearness  and  cloudiness,  and  this,  no  doubt,  has  an 
important  bearing  upon  many  meteorological  phenomena. 

An  excellent  illustration  of  these  principles  is  afforded  by  the 
fountain  of  Hiero,  as  it  is  called,  at  Schemnitz  in  Hungary.  A 
part  of  the  machinery  for  working  the  mines  consists  of  a  col- 
umn of  water  2 GO  feet  high,  which  presses  upon  a  large  volume 
of  air,  enclosed  in  a  tight  reservoir.  The  air  is  consequently 
enormously  compressed  by  the  immense  weight  of  the  water, 

245.  How  do  these  principles  explain  the  distribution  of  temperature  in  the  atmo- 
sphere ? 


THESE    PRINCIPLES    APPLIED  227 

amounting  to  8,089  atmospheres.  "When  a  pipe  communicating 
with  this  reservoir  of  air  rs  suddenly  opened,  it  rushes  out  with 
extreme  velocity,  and  instantly  expanding,  absorbs,  in  so  doing, 
so  much  heat  as  to  precipitate  the  moisture  it  contains  in  a 
shower  of  very  white,  compact  snow,  a  hat  held  in  the  blast 
being  immediately  covered  with  it.  So  strong  is  the  current 
of  condensed  air,  that  the  workman  who  holds  the  hat  is  obliged 
to  lean  his  back  against  the  bank  to  retain  it  in  its  position. 
The  snow  in  this  case  is  due  to  the  expansion  of  the  air,  and 
the  conversion  of  its  heat  of  temperature  into  latent  heat. 

245*.  The  Sudden  Expansion  of  Compressed  Air  is  Applied 
to  the  Manufacture  of  Ice.  Ice  machines.  Application  has  been 
made  of  the  cold  produced  by  the  sudden  expansion  of  com- 
pressed air  to  the  production  of  ice  for  commercial  purposes. 
The  air  is  first  made  to  pass  through  a  large  chamber  filled 
with  porous  materials  constantly  kept  moist  by  means  of  a 
stream  of  water  running  through  it,  and  is  thus  heavily  charged 
with  watery  vapor,  this  moist  air  is  then  powerfully  condensed 
by  a  large  forcing  pump  driven  by  a  steam  engine.  The  la- 
tent heat  which  is  evolved  by  this  violent  compression,  is  ab- 
sorbed, as  fa>t  as  set  free,  by  the  watery  vapor  which  the  air 
contains,  owing  to  the  immense  capacity  of  water  for  heat, 
§  236,  and  thus  the  temperature  of  the  air  is  prevented  from 
rising  to  the  height  to  which  it  does  in  the  Fire  Syringe.  §  244. 
It  is  still  further  cooled  by  being  made  to  pass  through  a  sec- 
ond chamber  filled  with  porous  materials  constantly  kept  moist 
by  running  water,  and  then  dried  by  transmission  through  an 
additional  chamber  filled  with  porous  substances  perfectly  dry,  to 
which  it  gives  up  any  moisture  that  it  may  have  carried  from  the 
previous  chamber.  It  is  then  allowed  to  expand  in  a  compara- 
tively large  chamber,  and  in  so  doing,  in  the  course  of  a  minute 
or  two  it  becomes  very  cold.  Thence  it  passes  on  into  a  long 
passage,  arranged  in  an  ice  house  protected  from  the  sun, 
above  which  are  placed  the  vessels  of  water  to  be  frozen,  where 
it  undergoes  a  sudden  and  very  great  expansion.  By  the  ex- 
pansion which  the  air  undergoes  in  passing  through  this 
tube,  FO  much  heat  is  absorbed  and  made  latent,  that  it  becomes 
intensely  cold,  the  water  in  the  pans  is  speedily  frozen  into 
thick  blocks,  and  a  very  large  quantity  of  air  confined  in  the 

What  is  the  average  rate  of  diminution  of  temperature  &s  we  ascend  above  the  sur- 
face? Account  for  the  formation  of  mists  and  clouds,  and  for  their  disappearance  on 
these  principles.  What  illustration  is  afforded  of  these  principles  by  the  fountain  of 
lliero,  at  ijchemnitz?  Account  for  the  formation  of  snow  when  the  compressed  air 
rushes  out. — 245*.  Describe  the  method  of  man ulac luring  ice  by  the  expansion  of  com- 
pressed air. 


228  TO    THE   MANUFACTURE    OF   ICE, 

ice-house  is  cooled  to  such  a  degree  as  to  become  extremely 
useful  for  refrigerating  purposes.  On  these  principles  a  ma- 
chine has  been  constructed  by  Windhausen,  in  Germany,  which 
is  capable  of  producing  4,800  Ibs.  or  more  than  2  tons,  every 
12  hours,  or  nearly  5  tons  in  21  hours,  at  a  cost  of  about  $2.94= 
for  2,000  Ibs.  Temperature  is  reduced  from  80°  to  —  18°  F. 

The  Windhausen  machine  has  been  still  further  improved  by 
Weld,  in  this  country.  rlhis  is  thought  to  be  the  most  success- 
ful method  of  producing  ice  by  artificial  means,  and  in  some 
respects  even  to  surpass  Carre's  machine.  It  possesses  four 
great  advantages  over  processes  in  which  Ammonia  and  other 
chemical  substances  are  employed;  first,  that  the  refrigerating 
agent  being  pure  air,  can  be  brought  into  direct  contact  with 
the  water  to  be  frozen,  without  the  intervention  of  tubes  and 
vessels,  as  is  the  case  with  Carre's  process,  and  has  therefore 
an  opportunity  to  exercise  a  much  greater  cooling  effect;  sec- 
ond, that  if  any  leak  takes  place  nothing  can  escape  that  will 
tend  to  injure  the  articles  intended  to  be  cooled  or  frozen,  while 
in  the  case  of  machines  depending  upon  the  use  of  special 
chemical  substances  a  sudden  leak  at  an  inopportune  moment 
might  result  in  the  destruction  of  a  large  amount  of  valuable 
material,  before  any  efficient  remedy  could  be  applied ;  third, 
the  cheapness  of  the  refrigerating  agent,  which  being  pure  air, 
can  always  be  had  in  a  perfect  s  afe  in  every  part  of  ihe  globe; 
fourth,  the  comparatively  low  pressure  required  for  condensing 
the  air,  and  consequently  the  much  less  strength  and  power  of 
resistance  required  in  the  apparatus  employed.  In  compressed 
air  refrigerating  machines  only  about  45  pounds  pressure  to  the 
square  inch  are  required,  while  in  Carry's  machine  from  120 
to  180  pounds  to  the  square  inch  are  necessary,  in  others  as 
much  as  800  or  1200  pound?.  Consequently  the  compressed 
air  machinesdo  not  require  to  be  nearly  as  strong,  and  are  much 
less  expensive.  The  cost  of  compression  is  also  much  reduced 
by  throwing  back  a  portion  of  the  elastic  power  of  the  com- 
pressed air  upon  the  main  shaft  so  as  greatly  to  reduce  the 
actual  power  required  for  condensation. 

In  view  therefore  of  the  low  first  co.*t  of  the  apparatus,  the 
cheapness  of  the  refrigerating  agent  and  its  purity,  the  facility 
of  compression,  and  the  large  scale  upon  which  the  process  can 

How  many  tons  can  be  produced  by  Windhausen "8  machine  per  diem?  At  what  cost 
per  ton  1  Have  the  compressed  air  machines  any  advantages  over  Carre's  machine  ? 
State  the  four  points  of  superiority.  How  can  the  thin  shetts  pf  ice  that  are  produced 
by  these  Ice-machines  be  made  into  thick  blocks  1 


AND  TO  THE  CONDENSATION  OF  VAPORS.       229 

be  carried  on,  this  method  of  manufacturing  ice  by  the  agency 
of  compressed  air  is  thought  to  possess  great  advantages  over 
those  which  depend  upon  chemical  agents. 

This  method  of  refrigeration  promises  therefore  to  be  of  great 
value  for  the  production  of  ice  in  hot  climates  where  no  natu- 
ral ice  is  formed.  It  must  be  remembered  however  that  by 
none  of  these  processes  are  blocks  of  ice  of  any  great  thickness 
formed,  rarely  more  than  three  or  four  inches,  but  blocks  of  any 
required  thickness  may  easily  be  formed  by  freezing  several  of 
them  togeiher. 

246.  The  condensation  of  Vapors  by  pressure  is  explained 
on  this  principle.  It  is  not  the  permanent  gases  alone,  whose 
temperature  is  raised  by  compression  and  diminished  by  ex- 
pansion. It  is  equally  true  of  vapors.  If  vapor,  after  being 
separated  from  the  liquid  that  forms  it,  be  compressed  into  a 
diminished  volume,  or  allowed  to  expand  into  an  increased  one, 
its  temperature  will  be  raised  in  the  one  case  and  lowered  in 
the  other,  and  at  the  same  time  its  elasticity  will  be  increased 
by  the  diminution  of  its  volume,  and  diminished  by  the  increase 
or' it.  It  has  been  stated,  §  202,  that  when  vapor  is  subjected  to 
mechanical  compression,  its  elastic  force  remains  unchanged, 
because  a  part  of  the  vapor  is  condensed  into  a  liquid.  It  is 
more  correct  to  say,  that  the  first  effect  of  mechanical  compres- 
sion upon  vapors  is  to  increase  their  temperature,  by  converting 
their  latent  into  sensible  heat.  Their  elasticity  is  at  the  same 
time  increased  in  proportion  to  the  pressure,  but  as  the  elevation 
of  their  temperature  above  that  of  the  surrounding  medium,  ren- 
ders it  very  easy  to  abstract  heat  from  them,  and  the  instant  any 
heat  is  abstracted,  a  portion  of  the  vapor  is  reduced  to  the  stale 
of  a  liquid,  this  increased  elasticity  is  almost  immediately  re- 
duced to  the  point  at  which  it  was  before  the  compression  took 
place,  and  no  perceptible  depression  is  produced  upon  the 
height  of  the  mercurial  column.  On  the  other  hand,  when  the 
mechanical  pressure  upon  the  vapor  is  removed,  it  immediately 
expands,  its  temperature  is  proportionally  lowered  by  the  con- 
version of  its  sensible  into  latent  heat,  heat  beg'ns  to  enter  it 
from  the  surrounding  medium,  a  portion  of  the  liquid  begins  to 
vaporize,  and  so  the  process  goes  on,  until  as  much  vapor  has 
been  formed  as  the  temperature  of  the  surrounding  medium  is 
able  to  sustain.  Consequently,  no  perceptible  elevation  takes 
place  in  the  height  of  the  mercurial  column,  because  the  increase 

246.  State  the  ei^ht  principles  that  may  be  deduced  from  the  above  mentioned  facts. 


230  SUMMARY. 

of  elasticity  produced  by  the  influx  of  heat,  keeps  pace  with  the 
diminution  produced  by  the  removal  of  mechanical  pressure. 
The  condensation  of  vapor  is  then,  in  all  cases,  due  to  the  ab- 
straction of  heat,  and  not  to  mechanical  compression,  just  as 
truly  as  the  formation  of  vapor  is  due  to  the  addition  of  heat.  In 
the  liquefaction  of  gases,  the  process  is  accomplished  by  depriv- 
ing them  of  heat  as  fast  as  their  temperature  is  raised  by  com- 
pression. In  this  manner,  so  much  heat  is  gradually  abstracted 
as  to  compel  them  to  assume  the  form  of  liquids.  In  all  case^, 
vapor  compressed,  rises  to  the  same  temperature  that  would 
be  necessary  to  produce  it, under  the  same  pressure,  by  the  di- 
rect application  of  heat.  Thus  the  vapor  raised  from  water  at 
the  temperature  of  68°  has  a  volume  58,224  times  greater  than 
the  water  which  produced  it.  Now  let  this  vapor,  having  been 
separated  from  the  water,  be  compressed  until  it  be  reduced  to 
the  volume  which  it  would  have  had  if  it  had  been  formed 
from  boiling  water,  i.  e.,  a  volume  only  1.696  times  greater  than 
that  of  the  water  which  produced  it,  and  its  temperature  will 
rise  from  68°  to  212°  by  the  conversion  of  its  latent  into  sen- 
sible heat,  i.  e.,  exactly  the  temperature  it  would  have  been 
necessary  to  give  it,  if  it  had  been  formed  in  the  first  place  of 
this  degrae  of  pressure  and  elastic  force.  This  is  a  conclusive 
proof,  that  the  sum  of  the  sensible  and  insensible  heat  in  vapor 
is  the  same,  whatever  the  temperature  at  which  it  may  have 
been  formed. 

247>  Summary  of  Principles.  Applications.  Illustrations. 
From  the  phenomena  presented  by  liquefaction,  vaporization, 
solidification,  and  the  compression  and  expansion  of  solids, 
liquids  and  gases,  we  may  deduce  the  following  important  prin- 
ciples : — 

1.  Change  of  density  always  produces  change  of  temper- 
ature. 

2.  If  a  body  pass  from  a  denser  to  a  rarer  condition,  or  from 
the  state  of  a  solid  to  that  of  a  liquid  or  a  vapor,  heat  is  ab- 
sorbed, and  the  temperature  of  surrounding  objects  sinks. 

3.  If  the  reverse  takes  place,  and  a  body  becomes  more 
dense  than  before,  or  passes  from  the  state  of  a  vapor  to  that  of 
a  liquid  or  solid,  as  when  steam  is  condensed  or  water  freezes, 
heat  is  given  forth,  and  the  temperature  of  surrounding  objects 
rises. 

4.  Mechanical  compression  raises,  and  mechanical  expansion 
diminishes  the  temperature  of  all  bodies,  solid,  liquid  and  gas- 
eous. 


EXPERIMENTS.  231 

5.  If  the  result  of.  mixing  two  liquids  be,  that  they  occupy- 
less  space  than  before,  heat  is  produced.     Four  parts,  by  weight, 
of  sulphuric  acid,  and  one  part,  by  weight,  of  water,  become 
condensed  when  mingled,  and  sufficient  latent  heat  is  set  free  to 
heat  the  mixture  above  the  boiling  point  of  water. 

6.  If  the  result  of  mixing  two  liquids  be,  the  production  of 
a  solid,  great  heat  is  produced.     One  or  two  drops  of  sulphu-ic 
acid  added  to  a  solution  of  chloride  of  calcium,  produces  a  solid, 
and  gives  forth  a  large  amount  of  heat. 

7.  If  a  solid  be  dissolved  in  water,  cold  results.     Nitrate  of 
ammonia  thrown  into  water  will  be  at  once  dissolved,  and  great 
reduction  of  temperature  will  take  place. 

8.  If  a  liquid  be  added  to  a  solid,  and  be  at  once  absorbed, 
heat  results.     If  quicklime  be  thrown  into  water,  the  water 
disappears,  and  great  heat  is  produced,  sufficient  to  inflame 
matches,  and  set  fire  to  buildings  and  vessels. 

Many  other  phenomena  of  daily  occurrence  in  nature  and  the 
arts  may  be  explained  on  these  principles. 

Experiments:      Specific  Heat, 
k 

1.  Specific  Heat.     To  show  that  equal  amounts  of  heat,  added  to  different  sub- 
stances, increase  their  temperatures  unequally,  or  that  their  capacities  for  heat  are  dif- 
ferent, mix  1  Ib.  of  water  at  100°,  with  1  Ib  of  mercury  at  40°  :  the  temperature  of  the 
mixture  will  be  98°.     Then  mix  1  Ib.  of  mercury  at  100°,  with  1  Ib.  of  water  at  40°,  and 
the  temperature  of  the  mixture  will  be  42°  only.    The  same  amount  of  heat  has  been 
added  in  both  cases      Why  this  difference  of  result?    Because  the  water  has  a  greater 
capacity  for  heat  than  mercury. 

2.  Heat  balls  of  zinc,  copper,  tin,  iron,  lead,  of  the  same  weight,  to  the  same  degree, 
by  immersing  them  in  boiling  water,  and  then  dip  them  all  into  different  vessels,  of  the 
same  size,  all  containing  equal  weights  of  water  at  32°,  each  having  a  thermometer  in  it, 
and  note  the  different  heights  at  which  the  thermometers  stand  at  the  end  of  half  an 
hour. 

3.  This  experiment  may  be  varied  by  observing  the  times  occupied  by  the  different 
metals  in  raising  the  temperature  of  the  different  vessels  of  water  to  the  same  degree. 

4-.  Observe  the  amount  of  ice  melted,  and  water  formed,  by  the  cooling  of  equal 
weights  of  different  substances.  This  is  the  most  satisfactory  mode  of  ascertaining  spe- 
cific heat. 

1.  Change    of  State   produces    change    of  Temperature.    Mix  equal 
parts  of  snow  and  salt  together ;  great  cold  results  from  their  liquefaction. 

2.  Add  a  few  drops  of  sulphuric  acid  to  a  strong  solution  of  chlorohydrate  of  lime, 
(muriate  of  lime);a  solid  results,  and  great  heat  is  produced. 

3.  Add  water  to  quicklime  ;  a  solid  results,  and  great  heat  is  produced. 

4.  Potassium  and  sodium  pressed  together  in  a  mortar,  produce  a  liquid  alloy ;  add 
mercury,  and  this  liquid  solidifies,  and  heat  enough  is  produced  to  inflame  the  naphtha 
adhering  to  the  potassium. 

5.  Hammer  iron,  and  it  becomes  very  hot. 

6.  Compress   water  by  a  powerful  screw,  and  the  thermometer  rises ;  remove  the 
pressure,  and  it  sinks. 

7.  Compress  air  in  the  fire  syringe,  and  a  piece  of  well  dried  punk,  or  tinder,  will  be 
inflame!. 

8.  Exhaust  the  air  from  a  bell  glass,  by  the  air  pump,  and  the  thermometer  will  sink ; 
allow  the  air  to  enter  again,  which  is  the  same  thing  as  compressing  it,  and  the  ther- 
mometer will  rise. 

9.  Mix  equal  volumes  of  sulphuric  acid  and  water;  an  increase  of  density  results, 
with  gr«at  rise  of  temperature. 


232  THE    SOURCES    OF    HEAT. 

10.  Mix  equal  volumes  of  alcohol  and  water;  condensation  results,  and  rise  of  tem« 
perafcure. 


§  VII.    The  Sources  of  Heat. 

247.  The  Sources  of  Heat.    The  sources  of  heat  are  nu- 
merous, but  they  may  all  be  reduced  to  seven;  viz:  1st,  The 
Sun.     2d,  The  internal  heat  of  the  earth.     3d,  Chemical  action 
and   combustion.      4th,   Electricity.      5th,  The  absorption  of 
moisture.      6th,  Vital  action.     7th,  Mechanical  action. 

248.  The  Sun.    Of  all  the  sources  of  heat,  the,  sun  is  the 
most  intense.     The  cause  of  the  sun's  heat  is  unknown,  but  it  is 
probably  due  to  electrical  or  chemical  action.     The  amount  of 
heat  which  the  earth    receives  from  this  source  is  enormous. 
Faraday  has  calculated  that  the  average  amount  radiated  by 
the  sun  upon  an  acre  of  land,  on  a  summer's  day,  is  equal  to 
that  which  would  be  produced  by  the  combustion  of  sixty  sacks 
of  coal.     It  has  been  estimated  that  the  amount  of  solar  heat 
entering  the  atmosphere  of  the  earth  in  one  year,  is  sufficient 
to  melt  a  layer  of  ice  completely  enveloping  it,  from  90  to  100 
feet  in  thickness ;  of  this  amount  however,  the  earth  only  re- 
ceives about  two  thirds,  the  rest  being  absorbed  by  the  atmos- 
phere.    This  vast  amount  is,  however,  but  a  small  part  of  that 
radiated  by  the  sun ;  calculating  the  area  which  the  earth  pre- 
sents, and  its  mean  distance  from  the  sun,  it  has  been  found 
that  the  earth   does   not  receive  at  any  moment,   more  than 
5"!T¥T<5Wo  o  <r  Part  °f  tnat  which  the  sun  emits.     Indirectly  by 
the  various   effects   which  solar  heat  and  light  produce  when 
they  reach  the  earth,  the  sun  is  really  the  cause  of  that  which 
proceeds  from  some  of  the  other  sources  of  heat,  and  especially, 
that  produced  by  the  combustion  of  vegetable  matter. 

249.  The  Internal  heat  of  the  Earth.    Besides  the   heat 
which  it  is  receiving  from  the  sun,  the  earth  has  also  a  nucleus 
of  inten-ely  heated  matter  within  itself.     This  is  proved  by  the 
steadily  increasing  heat  of  the  earth  at  successive  dep:hs.     At 
30  or  40  feet  beneath  the  surface,  the  thermometer  is  unaffected 

247  How  many  sources  of  heat  are  there?  State  what  they  are. — 248.  Which  is  the 
most  intense  source  of  heat  ?  Wrhat  is  the  amount  of  heat  received  by  the  earth  from 
the  sun.  per  acre?  What  is  the  amount  per  annum,  that  enters  the  atmosphere?  Ho\v 
much  of  this  reaches  the  earth  ?  Ho^v  does  the  he.it  and  light  of  the  sun,  indirectly  pro. 
duce  the  he-it  that  seems  to  emanate  from  other  sources  ? — 249.  What  is  the  second  source 
of  he-it?  How  may  the  ducleus  of  heated  matter  iu  the  interior  of  the  earth  be  proved 
to  exist? 


COMBUSTION.  233 

by  the  variations  of  the  seasons.  As  we  proceed  below  this 
point  the  thermometer  ia  found  to  rise  progressively,  though  not 
uniformly  in  all  places,  at  the  average  rate  of  1°  F.  for  every 
50  feet  of  descent.  Some  have  estimated  the  rate  at  1°  for 
every  45  feet.  In  six  of  the  deepest  mines  of  the  north  of  Eng- 
land the  rate  is  1°  for  every  44  feet.  In  the  lead  mines  of 
Saxony  it  is  1°  for  every  60  feet,  arid  the  same  rate  was  ob- 
served in  boring  the  well  of  Grenelle  at  Paris.  At  ihis  rale 
the  temperature  of  the  earth  increases  100°  ibr  every  mile; 
consequently  at  one  mile  and  a  half  the  temperature  would  be 
as  high  as  that  of  boiling  water,  and  at  the  dcp;h  of  40  miles  a 
temperature  of  4000°  would  be  attained,  which  is  considerably 
above  the  melting  point  of  cast  iron  and  even  of  platinum,  and 
quite  sufficient  to  completely  fuse  all  known  mineral  sub  fauces. 
The  central  mass  of  the  earth  is  probably  now  in  a  state  of  ig- 
neous fluidity,  and  the  thickness  of  the  external  crust  is  not 
more  than  T£<y  its  radius,  about  the  thickness  of  a  sheet  of  paper 
upon  a  twelve  inch  globe.  This  thin  crust  is  however  fc'o  poor 
a  conductor  that  the  central  heat  is  hardly  felt  on  the  surface, 
and  it  has  been  calculated  that  it  does  not  elevate  the  mean 
temperature  of  the  surface  more  than  ^  of  a  degree.  It  must 
however,  exert  a  powerful  effect  in  keeping  up  the  general  tem- 
perature of  the  globe. 

250.  Chemical  action,  Combustion-  Chemical  combination 
is  generally  accompanied  with  the  evolution  of  heat,  and  this 
constitutes  the  chief  source  of  artificial  heat.  When  the  com- 
bination takes  place  slowly,  as  when  iron  oxidises  in  the  air, 
the  heat  disengaged  is  imperceptible,  but  when  it  proceeds  rap- 
idly the  disengagement  of  heat  is  very  intense,  and  combustion 
ensues.  Kvery  chemical  combination  which  is  attended  with 
the  disengagement  of  heat  and  light  is  called  combustion.  In 
the  case  of  wood,  coal,  oil,  gas,  &c.,  it  is  the  combination  of  car- 
bon and  hydrogen  with  the  oxygen  of  the  air  which  produces 
the  heat  and  light.  But  there  are  numerous  instances  of  com- 
bination in  which  oxygen  plays  no  part,  as  when  me'allic  anti- 
mony is  dropped  in  powder  into  a  jar  of  chlorine,  or  pho  phorus  • 
is  mixed  with  iodine.  The  quantity  of  heat  produced  by  com- 
bustion varies  greatly  with  the  nature  of  the  substances  em- 

What  is  the  rate  of  increase?  At  this  rate  -what  is  the  temperature  at  the  cbpth  of  40 
miles?  How  much  of  this  heat  reaches  the  surf  ice  of  tlae  earta  !  What  eit'ei-t  has  it 
upon  the  general  temperature  of  the  globe?— 2^0.  What  is  the  third  source  of  heat? 
What  is  combustion?  In  the  case  of  the  combustion  of  coal,  oil.  &c  ,  what  el-mtnts  by 
their  combination  produce  the  heat?  TO  what  Js  the  amount  of  heat  produced  in  all 
cases  of  combustion  proportioned? 


234  ELECTRICITY. 

ployed,  but  it  is  always  constant  for  the  same  substances,  and 
proportioned  exactly  to  the  weight  of  each  which  is  consumed. 
The  amount  of  heat  produced  is  by  no  means  proportional  to  the 
light.  The  flame  of  hydrogen  is  that  which  produces  the  most 
heat  of  any  known  combustible,  but  its  light  is  so  feeble  that  it 
can  hardly  be  seen  in  the  day  time.  The  following  table  gives 
the  amount  of  heat  produced  by  various  combustible  substances 
when  they  burn  in  the  air.  The  thermal  unit  is  the  heat  neces- 
sary to  raise  a  weight  of  water  equal  to  that  of  the  combustible,  1°. 

Table  of  Heat  produced  by  various  Combustibles, 

Hydrogen,       .....  34.462  units  of  heat. 

Light.  Carb.  Hydrogen,    ....  13.063 

Illuminating  Gas,         ....  11.858 

Beeswax,  ......  10.496 

Spermaceti,      .....  10.342 

Turpentine,  .  .  .  .  .  10.662 

Alcohol,  .  .  .  .      f      .     4  7.184 

Wood  Charcoal,    .....  8,080 

Coke,  .  .  .-'.-."•»        '     .  8.047 

251.  Electricity-    This  is  another  source  of  intense  heat, 
whether  produced  by  the  electrical  machine  or  by  the  galvanic 
battery.     Gunpowder  may  be  inflamed  and  gases  may  be  fired 
by  a  single  spark,  however  small,  from  the  electrical  machine, 
and  the  heat  produced  by  the  galvanic  battery  is  far  greater 
than  that  proceeding  from  any  other  artificial  source.     If  the 
wires  from  the  poles  of  a  powerful  battery  be  tipped  with  well 
burned  charcoal  and   brought  near  each  other,  a  continuous 
current  of  electricity  passes,  producing  intense  light,  and  heat 
sufficient  to  fuse  the  precious  stones,  and  dissipate  the  metals  in 
vapour.  '  '-; 

252.  The  Absorption  of  Liquids  and  Gases.    The  simple 
act  of  moistening  any  dry  substance  is  attended  with  a  slight 
disengagement  of  heat.     With  mineral  substances  reduced  to 
fine  powder  and  wetted,  the  rise  of  temperature  does  not  ex- 
ceed one  or  two  degrees,  but  with  vegetable  and  animal  sub- 
stances, such  as  cotton,  hair,  wool,  ivory,  dried  paper,  &c.,  the 
rise  of  temperature  varies  from  2°  to  10°  or  11°  F.     The  ab- 
sorption of  gases  by  solid  bodies  gives  rise  to  the  same  phe- 

What  substance  produces  the  greatest  amount  of  heat  in  burning?  Give  the  table 
of  the  amount  of  fyeat  produced  by  different  combustibles,  What  is  the  thermal  unit 
in  the  above  table?— 251.  State  the  fourth  source  of  heat.  What  heating  effect  can  be 
produced  by  the  electrical  spark,  by  the  galvanic  battery  ? — 252.  What  is  the  fifth  source 
of  heat  ?  State  the  heating  effect  produced  by  the  absorption,  of  moisture  by  cotton, 
hair,  wool,  &c.,  by  the  absorption  of  gases? 

10* 


MECHANICAL    ACTION.  235 

ttomcma.  If  platinum,  in  the  state  of  platinum  black,  be  placed 
in  oxygen  gas  the  metal  will  absorb  several  hundred  times  its 
weight  of  the  gas,  and  its  temperature  will  rise  high  enough  to 
produce  intense  combustion.  In  like  manner,  if  a  jet  of  hy- 
drogen gas  be  directed  upon  a  bit  of  spongy  platinum  suspended 
in  the  air,  it  will  almost  immediately  take  fire  from  the  heat 
produced  by  the  absorption  of  the  gas. 

253.  Vital  action.    Both  plants  and  animals  produce  a  con- 
tinued and  definite  amount  of  heat,  by  means  of  which  their 
temperature  is  sustained  considerably  above  that  of  the  sur- 
rounding medium.     This  may  be  regarded  as  strictly  due  to  the 
chemical  action  which  at  all  times  is  going  on  within  the  vege- 
table and   animal  economy,  regulated,  however,  by  the  vital 
power.     There  is,  during  life,  a  steadily  continued  combination 
going  on  between  the  carbon  and  hydrogen  of  the  tissues,  and 
the  oxygen  of  the  air.     This  is  a  case  of  combustion,   and 
strictly  analogous  to  the  burning  of  coal  and  gas  in  the  air,  for 
the  same  amount  of  heat  is  produced  by  an  equal  we'ght  of  the 
elements  employed  in  both  cases,  the  only  difference  being,  that 
in  the  one  case  the  heat  is  produced  rapidly,  in  the  other,  slowly. 

254.  IKEechanical  action.— Friction  and  Percussion.— The 
mechanical  equivalent  of  Heat.    The  friction    of  two    bodies 
against  each  other  produces  an  amount  of  heat  proportioned 
to  the  pressure  employed  and  the  rapidity  of  the  movement. 
Among  savage  nations  the  friction  of  two  pieces  of  wood  is  used 
as  a  means  of  lighting  a  fire,  and  the  heating  of  machinery, 
and  the  ax'es  of  carriages  and  of  locomotives,  even  to  the  point 
of  igniting  combustible  sub-tances  placed  near  them,  is  a  matter 
of  daily  occurrence.     Sir  H.  Davy  melted  two  blocks  of  ice  by 
causing  them  to  be  rubbed  violently  against  each  other,  in  a 
vacuum,  at  a  temperature  below   32°.    Count   Rumford  suc- 
ceeded in  boiling  water  by  the  friction  from  the  boring  of  a 
cannon;  a  blunt  steel  borer  was  made  to  press  against  the  end 
of  the  cannon,  and  surrounded  by  a  box  containing  18|  Ihs.  of 
water,  in  which  a  thermometer  was  placed.     The  original  tem- 
perature of  the  water  was  60° ;  in  an  hour  the  temperature  of 
the  water  had  risen  to  107°  ;  in  one  hour  and  a  half,  to  142° ; 
in  two  hours  to  178°,  and  in  two  hours  arid  a  half  from  the  com- 
mencement of  the  experiment,  the  water  rose  to  212°,  and  ac- 

253.  What  is  the  sixth  source  of  heat?  To  what  is  the  heat  produced  by  this  source 
Strictly  due?  What  combustion  is  continually  going  on  in  the  bodies  of  animals  a.  d 
plants?— 254.  What  is  the  seventh  source  of  heat?  Explain  the  heat  of  friction,  Pe» 
scribe  Sir  II.  Davy's  experiment,  Count  llqroford's. 


236  THE    MECHANICAL 

tually  began  to  boil.  An  apparatus  has  been  invented  in 
France,  for  generating  steam  by  means  of  heat  generated  by 
friction.  Mr.  Tyndall  succeeded  in  milking  water  boil  in  two 
minutes  and  a  half,  in  a  brass  tube  which  was  made  to  revolve 
very  rapidly  between  two  pieces  of  oak,  compressed  tightly 
around  it,  and  the  cork  with  which  the  tube  was  stopped  was 
projected  twenty  feet  into  the  air  by  the  pressure  of  the  steam. 
Percussion  is  a  combination  of  friction  and  compression,  and  often 
produces  intense  heat,  as  when  the  particles  of  steel  detached 
by  the  flint,  in  the  use  of  the  ordinary  tinder  box,  are  ignited 
by  the  heat  evolved  by  the  sudden  collis'on.  Iron  may  be  heat- 
ed red  hot  by  hammering,  and  bars  of  bra^s  and  copper  which 
were  quite  cold  when  subjected  to  the  pressure  of  the  rolling 
mill,  often  issue  in  an  extremely  heated  state.  The  heat  derived 
from  this  source  is,  as  has  been  previously  stated,  the  heat  pre- 
viously lafent  in  these  substances  converted  into  heat  of  tem- 
perature by  the  increase  of  density  produced  by  compression. 
It  is  remarkable  that  the  supply  of  heat  from  this  source  seems 
to  be  almost  unlimited.  The  quantity  of  heat  developed  by 
friction  is  dependent  solely  upon  the  amount  of  force  expended, 
and  not  upon  the  nature  of  the  substances  rubbed  together.  It 
was  ascertained  by  Mr.  Joule  that  wl\en  water  was  agitated  by 
maans  of  a  brass  paddle  wheel,  the  expenditure  of  an  amount  of 
force  sufficient  to  elevate  772  Ibs.  to  the  height  of  1  foot,  had 
the  effect  of  raising  the  temperature  of  1  Ib.  of  water,  1°.  When 
iron  was  rubbed  against  iron  the  expenditure  of  an  amount  of 
force  sufficient  to  elevate  775  Ibs.  to  the  height  of  1  foot,  had 
tli3  effect  of  raising  the  temperature  of  1  Ib.  of  water,  1°.  When 
mercury  was  agitated  by  a  cast  iron  paddle  wheel,  1  Ib.  of  water 
was  raised  in  temperature  1°  by  the  expenditure  of  an  amount 
of  force  sufficient  to  elevate  774  Ibs.  to  the  height  of  1  foot.  The 
conclusion  deduced  was  that  the  mechanical  force  adequate  to 
raise  772  Ibs.  to  the  height  of  1  foot,  produced  sufficient  heat  to 
elevate  the  temperature  of  1  Ib.  of  water  from  55°  to  56°,  i.  e., 
by  1°.  There/  is  good  reason  to  believe  that  the  reverse  is  also 
true.  That  the  heat  which  \vill  raise  the  temperature  of  1  Ib. 
of  water  1°,  will  exert  a  mechanical  force  sufficient  to  raise  772 
Ibs.  to  the  height  of  1  foot,  or  is  equivalent  to  this  amount  of 

Mr.  Tyndall's.  Explain  the  striking  of  sparks  by  the  flint  and  steel.  In  there  any  limit 
to  the  amount  of  heat  which  can  be  produced  by  friction?  Does  the  heat  produced  de- 
pead  upon  the  nature  of  the  substance  employed,  or  upon  the  amount  of  force?  How 
was  this  proved  ?  How  much  heat  is  produced  by  a  mechanical  force  sufficient  to  raise 
773  Ibs  one  foot  high?  How  much  mechanical  force  is  produced  by  an  amount  of  heat 
which  will  heat  1  Ib  of  water,  1°.  State  the  mechanical  equivalent  of  heat, 


EQUIVALENT    OF    HEAT.  237 

mechanical  force.  This  amount  of  force,  viz :  772  Ibs.  elevated 
to  the  height  of  1  foot,  is  consequently  called,  the  mechanical 
equivalent  of  htat. 

Experiments. 

1.  Sources  of  Heat.    The  heat  of  the  sun  may  be  shown  by  condensing  its  rays 
upon  some  inflammable  material  by  an  ordinary  burning  glass. 

2.  The  heat  of  combustion  may  be  shown  by  the  inflammation  of  the  ordinary  illu- 
minating gas  of  cities. 

3.  Tne  heat  of  Electricity,  by  passing  the  charge  of  a  Leyden  jar  through  a  jet  of 
illuminating  gas,  as  it  issues  into  the  air.     For  this  purpose  let  a  wire  be  attached  to  the 
stem  of  the  burner,  ascend  by  its  side  and  rise  two  inches  above  it;  then  let  it  curve 
at  right  angles,  and  terminate  in  the  center  of  the  ascending  column  of  gas  ;  bring  the 
knob  of  the  Leyden  jar  near  to  the  end  of  the  wire,  so  that  the  charge  will  pass  directly 
through  the  gas      It  will  be  inflamed. 

4.  Chemical  action  produces  heat,  shown  by  pouring  1  ounce  of  Chlorohydric  acid 
on  1  ounce  of  Ammonia  ;  also  by  rubbing  together  Sulphur  and  Caustic  Potash,  equal 
parts,  in  a  mortar.    The  Acid  should  be  poured  from  a  vessel  tied  to  a  stick  several  feet 
long. 

5.  Mechanical  act:on  produces  heat,  shown  by  boring  a  hole  with  a  common  gimlet, 
in  wood,  and  then  applying  the  iron  to  a  piece  of  phosphorus.    It  will  be  inflamed. 

6.  The  same  may  be  shown  by  the  compression  of  Air  in  the  Fire  Syringe. 

7.  Also  by  the  admission  of  air  into  an  exhausted  Receiver,  containing  a  Thermom- 
eter, 


§  VIII.    The  nature  of  Beat. 

255.  The  material  theory  of  Heat.  There  are  two  theo- 
ries in  regard  to  the  nature  of  heat.  The  first  regards  heat  as 
an  extremely  subtile  form  of  matter,  and  possessed  of  all  its 
common  properties  except  weight;  able  to  enter  into  combi- 
nation with  bodies,  and  producing,  when  it  does  so,  the  phe- 
nomena of  expansion,  liquefaction  and  vaporization.  •  It  is  sup- 
posed to  be  a  fluid,  and  to  pass,  with  great  celerity,  from  one 
body  to  another,  whenever  they  are  brought  into  actual  contact. 
When  an  appreciable  interval  separates  two  bodies,  heat  is 
thought  to  pass  from  one  to  the  other  with  the  velocity  of  light. 
Its  particles  are  supposed  to  be  very  highly  repulsive,  and  to 
have  a  strong  tendency  to  fly  apart,  so  that  when  it  enters  an- 
other substance  it  necessarily  tends  to  separate  the  particles  of 
which  it  is  composed,  and  to  expand  the  body.  Being  destitute 
of  weight,  heat  is  called  an  Imponderable.  The  theory  of  the 
material  nature  of  heat  is  chiefly  supported  by  the  phenom- 
ena of  liquefaction  and 'vaporization,  in  which  heat  seems  to  en- 

255.  How  many  theories  are  there  in  regard  to  the  nature  of  heat?     Describe  the  ma- 
terial theory.     On  what  is  this  theory  chiefly  supported? 


238  THE    NATURE    OF    HEAT. 

ter,  in  certain  regular  proportions,  into  composition  with  other 
forms  of  matter,  and  to  produce  new  substances  differing  from 
their  C3inponent  elements  in  most  of  their  physical  properties. 
In  this  respect  there  certainly  is  a  close  analogy  between  heat 
and  other  kinds  of  matter.  The  material  theory  of  heat,  is  the 
one  which  has  been  generally  received  until  within  a  short  time. 

256.  The  mechanical  theory  of  Heat.    The  second  theory 
is  called   the  mechanical   theory  of  Heat.      It  supposes  that 
heat  is  altogether   immaterial   in   its  character,  and  simply  a 
force  produced  by  the  vibrations  of  the  molecules  of  bodies,  or 
the  infinitely  small  particles  of  whii'h  matter  is  believed  to  be 
made.      The  essence  of  heat  is  thought  to  consist  in  motion,  so 
that  it  is  always  produced  by  motion,  and  also,  itself  al.vays 
generates  motion.     The  infinitely  small  particles  of  which  bod- 
ies consist,  are  thought  to  be  in  a  state  of  constant  vibration,  or 
to  have    a   never  ceasing  oscillating  motion.     This  motion  is 
supposed  to  be  the  cause  of  heat,  and  when  it  exceeds  a  cer- 
tain rate,  to  produce  the  sensation  and  all  the  other  common 
effects  of  heat.     According  to  this  view,  heat  is  a  mode  of  mo- 
tion.    This  is  the  theory  which  was  suggested  by  Count  Rum- 
ford,  towards  the  latter  part  of  the  last  century,  supported  by 
Sir  H.  Davy,  and  has  been  revived  by  Messrs.  Grove,  Joule, 
and  especially  by  Mr.  Tyndall.  within  a  few  years. 

257.  Proof  that  heat  is  produced  by  motion.       This    is 
proved    by   the   numerous    instances    in   which    heat   results 
from  the  arrest  of  motion.     If  a  lead  ball  be  allowed  to  fall 
from  a  great  height  upon  an  iron  plate,  it  is  flattened  by  the  fall, 
its  motion   completely  checked,  and   its  temperature  will,  at 
the  same  time,  be  found  to  be  considerably  elevated.     The  mo- 
tion seems  to  have  been  transformed  or  converted  into  heat.     In 
like  manner,  if  a  railway  train  under  full  headway,  be  stopped 
by  the  application  of  the  brakes,  a?  the  mot'.on  is  retarded,  great 
heat  is  manifestly  produced,  and  even  the  ignition  of  the  wood 
and  leather  with  which  the  wheels  are  pressed.     When  mer- 
cury is  repeatedly  poured  from  one  vessel  to  another,  its  motion, 
in  each  case,  being  suddenly  arrested  by  dashing  against  the 
sides  of  the  vessel,  its  temperature  is  perceptibly  elevated.     In 
like  manner,  if  air  be  blown  violently  against  a  fixed  obstacle, 


256  What  is  the  second  theory  1  Describe  it.  Who  have  been  some  of  the  principal 
supporters  of  this  theory  ?— 257.  Give  some  of  the  proofs  that  heat  is  the  result  of  motion. 
If  a  le:id  ball  be  allowed  to  fall  from  a  great  height,  what  effect  is  produced  upon  its 
temperature?  If  mercury  be  poured  from  one  vessel  to  another?  If  a  railway  train,  iu 
rapid  motion,  be  suddenly  stopped  ?  Give  other  instances. 


THE  MECHANICAL  THEORY  OF  HEAT.         239 

the  temperature  of  the  latter,  as  well  as  of  the  air,  if  tested  by 
a  delicate  thermo-multiplier,  will  be  found  to  be  considerably 
raised.  The  same  fact  is  also  conclusively  shown  by  the  exper- 
iment of  Count  Rumford,  already  described,  upon  the  boiling  of 
water  in  the  boring  of  cannon.  It  is  even  asserted,  with  con- 
siderable confidence,  that  the  water  of  the  cataract  is  heated  by 
its  fa1!,  and  that  of  the  ocean  by  the  agitation  of  its  waves. 

258.  Proof  that  motion  is  produced  by  heat.     This  is  shown 
in  the  effect  which  is  produced  upon  the  dimensions  of  bodies 
whenever  heat  enters  them.     The  particles  are  invariably  moved 
farther   apart,    and    the   bodies   expanded.       If    the    heat,  in 
the  case  of  a  solid,  be  pushed  to  the  point  of  liquefaction,  a  fur- 
ther movement  takes  place,  and  the  particles  a^e  removed  so 
far  from  each  other  as  to  be  susceptible  of  a  ready  interchange 
of  place.     Finally,  if  the  heat  be  urged  so  far  as  to  produce  va- 
porization, a  still  further  movement  is  produced  in  the  particles, 
and  they  become  actually  self-repellent  and  elastic.     The  mo- 
tion of  the.  steam-engine  is  altogether  the  result  of  the  heat  de- 
rived from  the  fire  of  the  furnaces.     So  is  the  motion  of  the 
caloric-engine  of  Ericsson.     The  heat  of  combustion  is  supposed 
to  be  produced  by  the  violent  clashing  of  the  particles  of  carton 
and  hydrogen,  of  which  common  combustible  matter  is  composed, 
and  the  oxygen  of  the  air.     The  mechanical  motion  imparted  to 
these  particles  by  the  force  of  chemical  affinity  tending  to  draw 
them  together,  is  converted  into  the  peculiar  kind  of  motion 
producing  the  sensation  and  the  effects  which  we  call  heat.     In 
all  cases  therefore,  the  general  effect  of  heat  is  the  production 
of  motion,  and  vice  versa,  heat  is  always  produced  by  mo  lion. 
They  are  therefore  convertible  one  into  the  other. 

259.  Heat  not  the  sole  cause  of  motion,  while  motion  is 
the  sole  cause  of  heat.    Though  motion  is  produced  by  heat, 
heat  is  not  the  sole  cause  of  motion.     There  are   many  other 
sources  of  motion  besides  heat,  such  as  gravity,  electricity,  and 
animal  contractility ;  but  heat  is  thought  to  be  only  produced  by 
motion.     Motion  is  regarded  as  the  natural  state  of  the  mole- 
cules of  matter.     These  are  believed  to  be  constantly  in  motion, 
even  when  the  body  of  which  they  are  a  part,  is  at  rest ;  and  u  hen 
this  motion  is,  from  any  cause,  quickened  beyond  a  certain  de- 

258.  Prove  that  motion  is  produced  by  heat.  Show  that  this  is  the  case  in  expan- 
sion, liquefaction  and  vaporization.  The  steam  engine.  The  caloric  engine.  Are  heat 
and  mechanical  force  mutually  convertible? — 259.  Is  heat  the  sole  cause  rf  n>otion? 
On  the  other  hand  is  motion  the  sole  cause  of  heat,  according  to  the  mechanical  theory  ? 
What  proportion  exists  between  the  heat  produced  by  a  definite  amount  of  mechanical 
motion  and  the  motion  produced  by  the  same  amount  of  heat  ? 


240  SATISFACTORILY   EXPLAINS 

gree,  heat  is  the  result.  Consequently,  mechanical  motion  is 
spoken  of  as  the  cause  of  heat,  by  which  is  meant,  that  it  is  the 
sole  cause,  while  heat,  on  the  other  hand,  is  never  spoken  of  in 
this  sense,  as  the  sole  cause  of  motion. 

260.  The  amount  of  Heat  produced  by  a  definite  amount 
of  mechanical  motion,  and  the  Mechanical  Klotion  produced 
by  the  same  amount  of  heat,  are  precisely  equal.  It  has 
been  shown  that  the  amount  of  force  produced  by  the  fall  of 
772  Ibs.  through  1  foot,  is  sufficient  to  raise  the  temperature  of 
1  Ib.  of  water  1°  F.  i.  e.,  this  is  the  amount  of  heat  which 
would  be  generated  if  a  772  Ib.  weight,  after  having  fallen 
through  1  foot,  had  its  moving  force  destroyed  by  collision 
with  the  earth.  Conversely,  it  has  been  shown,  that  if  the  force 
produced  by  a"n  amount  of  heat  which  would  elevate  the  tem- 
perature of  1  Ib.  of  water  1°  were  all  concentrated,  it  would 
be  sufficient  to  raise  772  Ibs.  1  foot  into  the  air.  From  these 
facts  we  draw  the  conclusion  that  the  heat  produced  by  motion, 
and  the  motion  produced  by  heat,  are  not  simply  accidental 
circumstances,  but,  that  there  is,  in  these  cases,  a  certain  definite 
amount  of  mechanical  motion  converted  into  the  motion  which 
we  call  heat,  which  ceases  to  appear  any  more  as  mechanical 
motion ;  and  on*the  other  hand,  a  certain  definite  amount  of 
heat  motion  converted  into  mechanical  motion,  and  which  ceases 
to  appear  any  more  as  heat.  These  forces  are  not  lost  or  de- 
stroyed, but  merely  converted  from  one  kind  of  force  into  the 
other,  and  may  be  recovered  again  by  the  contrary  conversion. 
It  follows  from  this,  that,  in  all  cases  where  heat  is  used  to  pro- 
duce motion,  as  in  the  case  of  the  steam  engine,  an  amount  of 
heat  disappears  or  is  used  up  proportionate  to  the  mechanical 
effect  produced.  It  is  believed  that  the  heat  possessed  by  the 
s -earn  when  it  enters  the  cylinder  of  the  high  pressure  steam 
engine,  is  not  all  found  in  the  steam  which  issues  from  the  same 
cylinder,  after  the  piston  has  been  moved,  but  that  a  portion  of 
this  heat  has  been  consumed  and  converted  into  mechanical 
motion,  and  that  this  mechanical  motion  in  spending  itself,  has 
produced  again  an  equal  amount  of  heat,  by  friction,  in  the  vari- 
ous parts  of  the  machine.  According  to  the  material  theory  of 
heat,  none  of  the  heat  of  the  steam,  which  is  used,  is  consumed, 

230.  What  is  the  amount  of  mechanical  motion  produced  by  the  heat  necessary  to 
raise  1  Ih.  of  water  1°?  Conversely,  what  is  the  heat  produced  by  the  mechanical  force, 
necessary  to  raise  772  Ibs.  1  foot?  When  heat  is  used  to  produce  motion,  does  tha 
•whole  of  the  heat  appear  at  the  conclusion  of  the  process,  or  htis  a  part  been  consumed 
in  producing  the  motion?  Illustrate  this  iu  the  case  of  the  steam  engine.  Is  the  heat 
•which  exists  in  the  steam  when  ic  enters  the  cylinder  of  a  high  pressure  engine  all  found 
iu.  it  when  it  leaves  the  cylinder  ?  If  not,  what  has  become  of  it  I 


MANY    COMMON    PHENOMENA.  241 

but  the  whole  is  found  in  the  steam  which  issues  from  the  cylin- 
der, and  may  be  collected  in  the  condenser.  The  mechanical 
motion,  according  to  this  view,  is  not  due  to  the  conversion  of 
heat  into  motion,  but  merely  to  its  expansive  effect  in  passing 
from  the  boiler  to  the  condenser. 

261.  Some  of  the  common  phenomena  of  heat  explained 
upon  the  mechanical  Theory.  According  to  this  theory,  the 
particles  of  bodies  being  in  a  state  of  incessant  vibration,  heat  is 
supposed  to  be  produced  by  increase  in  the  intensity  of  the  motion. 
When  the  atoms  move  beyond  a  certain  determined  velocity,  and 
the  vibrations  become  more  extended,  the  heat  evolved  pushes  the 
particles  apart  and  separates  them  from  each  other,  thus  causing 
the  body  in  question  to  increase  in  volume,  and  producing  expan- 
sion. When  the  vibrations  of  the  particles  become  sufficiently 
extensive,  they  are  then  loosened  from  each  other  to  such  a  de- 
gree as  to  be  able  freely  to  interchange  places,  and  liquefaction  is 
the  result.  When  the  vibrations  are  pushed  so  far  that  the  par- 
ticles are  separated  too  far  from  each  other  for  cohesion  to  bind 
them  together,  they  become  self-repellent  arid  elastic,  and  the 
vaporous  state  is  produced.  When  a  hot  body,  whose  particles 
are  in  a  state  of  vibration,  is  brought  near  to  another,  colder 
than  itself,  the  vibration  is  communicated  to  the  particles  of  the 
second  body,  which  are  thus,  in  their  turn,  set  in  motion,  or 
conduction  takes  place.  When  heat  is  radiated  it  is  supposed 
that  the  oscillating  motion  of  the  particles  of  the  hot  body  is 
communicated  to  the  particles  of  a  very  fine  and  delicate  ether 
pervading  all  space,  which,  as  soon  as  they  begin  to  vibrate, 
produce  a  succession  of  undulations,  that  are  propagated  in 
ri.irht  lines  until  they  reach  some  material  obstacle,  to  the  par- 
ticles of  which  their  motion  is  then  communicated.  This  is 
supposed  to  be  the  mode  in  which  radiant  heat  is  propagated 
through  spacer  and  made  to  affect  the  temperature  of  bodies  on 
which  it  falls.  When  a  solid  body  is  liquefied,  it  is  well  known  that 
a  large  amount  of  heat  becomes  latent,  which,  it  has  been  thought, 
combines  with  the  solid,  in  order  to  form  the  liquid.  According 
to  the  mechanical  theory,  this  heat  is  not  stored  or  combined, 
but  has  been  simply  expended  or  used  up  in  forcing  the 
particles  of  the  body  apart,  i.  e.,  in  the  production  of  a  certain 
amount  of  motion,  and  when  these  particles  approach  each  other 

2<VL.  Explain  liquefaction  according  to  the  mechanical  theory  of  heat.  Vaporization. 
Conduction.  Radiation.  Explain  the  disappearance  of  heat,  or  heat  made  latent  in 
li'jiicl/iction,  according  to  the  mechanical  theory  ;  also,  the  heat  made  latent  hi  -vapori- 
zation. 


242  HEAT    MAY   BE 

again,  and  the  liquid  returns  to  the  solid  state,  the  motion  which 
then  takes  place  reproduces  exactly  the  amount  of  heat  which 
had  been  consumed.  The  same  thing  takes  place  in  the  case 
of  vaporization;  there  is  no  heat  combined  or  made  latent,  but 
there  is  a  larger  amount  expended  and  used  up  than  in  the  case 
of  liquefaction,  and  this  is  again  reproduced  when  the  particles 
of  the  vapour  move  near  to  each  other  for  the  purpose  of  re- 
suming the  liquid  or  solid  state.  Thus  all  the  common  phe- 
nomena of  heat  are  as  well  explained  by  the  mechanical  as  by 
the  material  theory  of  heat. 

262.  The  mechanical  theory  is  confirmed  by  several  sim- 
ple facts.  According  to  the  material  theory,  the  heat  evolved 
by  friction,  as  in  the  case  of  the  celebrated  experiment  of  Count 
Rumford,  when  water  was  boiled  in  the  process  of  boring  a  can- 
non, is  heat  previously  existing  in  the  solid  metal  of  the  cannon 
and  the  borer,  in  a  latent  state,  in  other  words,  is  a  part  of  their 
specific  heat  which  is  forced  to  appear  in  consequence  of  the  dimi- 
nution of  specific  heat  produced  by  compression.  If  this  were 
the  case  it  is  evident  that  the  specific  heat  of  the  chips  and  frag- 
ments of  metal,  produced  by  boring,  should  be  less  than  before, 
to  a  degree  sufficient  to  account  for  the  increase  in  the  temper- 
ature of  the  water.  Count  Rumford  ascertained  by  experiment, 
that  the  capacity  for  heat,  or  the  specific  heat  of  the  chips  had 
not  been  reduced,  but  was  precisely  what  it  was  before.  The 
material  theory  fails,  therefore,  of  explaining  the  heat  produced 
in  this  case,  and  the  only  supposition  that  we  can  adopt  is,  that 
the  effect  has  been  caused  by  the  motion  of  the  particles  produced 
by  compression,  and  by  the  mechanical  motion  of  the  borer,  convert- 
ed, in  part,  into  heat.  Again,  in  Sir  H.  Davy's  experiment,  §  254, 
in  which  two  blocks  of  ice  were  melted  into  water  by  the  heat 
generated  by  rubbing'  them  together  in  a  vacuum,  at  a  tem- 
perature below  32°,  the  explanation  given  by  the  material 
theory  is  the  same  as  in  the  last  case,  that  the  melting  is  pro- 
duced by  the  diminution  of  the  specific  heat  of  the  ice.  The 
specific  heat  of  the  water  formed,  ought  therefore  to  be  con- 
siderably less  than  that  of  the  ice,  but  instead  of  that,  its  specific 
heat,  or  its  capacity  for  heat  is  double;  it  is  impossible,  there- 
fore, that  the  heat  which  melted  the  ice  should  be  latent  heat, 
become  superfluous,  and  forced  to  appear,  because  the  water 

262  By  what  simple  facts  is  the  mechanical  theory  confirmed.  State  the  experiment 
of  Count  Rumford  of  boiling  water  by  means  of  friction ;  also,  Sir  H.  Davy's  experiment 
of  melting  ice  by  friction.  Show  how  both  are  explicable  upon  the  mechanica,!,  but 
inexplicable  on  the  material  theory  of  heat. 


CONVERTED    INTO    LIGHT.  243 

cou'd  not  retain  it.  It  is  certain,  also,  that  In  all  cases  when  ice 
is  melted,  there  is  an  enormous  amount  of  heat  absorbed,  and 
none  whatever  given  forth.  The  conclusion,  therefore,  is,  that 
the  melting  of  the  ice  is  due  to  the  conversion  into  heat  of  a 
part  of  the  mechanical  motion  employed. 

Lastly,  it  has  been  seen,  that  when  gases  are  rarefied  by  a 
diminution  of  pressure,  their  temperature  is  greatly  reduced, 
and  this  has  been  regarded  as  the  cause  of  the  low  tempera- 
ture which  prevails  in  the  higher  regions  of  the  atmosphere. 
The  explanation  riven,  has  been  that  the  specific  heat  of  rarefied, 
is  much  greater  than  that  of  condensed  air,  and  the  demand  for 
heat,  caused  by  the  expansion,  is  satisfied  at  the  expense  of  the 
heat  of  temperature.  It  has  been  ascertained,  however,  from  a 
calculation  of  the  weight  of  the  atmosphere,  raised  by  the  ex- 
pansion of  a  heated  body  of  air  confined  in  a  cylinder,  under  a 
piston  moving  freely,  and  open  to  the  air  above,  that  the  amount 
of  heat  of  temperature  which  disappears,  is  exactly  propoi  tioned 
to  the  weight  raised,  or  the  mechanical  motion  produced,  and  that 
these  are  in  the  precise  proportion  of  772  Ibs.  rnisfd  1  foot  for 
an  amount  of  heat  sufficient  t  heat  1  Ib.  of  water  by  1°  F.  It 
seems  evident,  therefore,  that  the  diminution  of  temperature  in 
the  case  of  expanding  air,  is  due  to  the  consumption  of  heat, 
and  its  conversion  into  the  mechanical  motion  of  the  molecules 
in  the  act  of  expansion ;  and  the  exact  agreement  of  the  propor- 
tion of  heat  to  motion  in  this  particular  case,  with  the  calculated 
proportion  between  heat  and  motion  in  the  determination  of  the 
mechanical  equivalent  of  heat,  §  254,  furnishes  a  very  strong 
argument  in  favor  of  th.3  mechanical  theory  of  heat. 

263.  Heat  may  be  converted  into  Light.  If  wre  inten  ify 
the  vibrations  of  heat  in  any  body,  we  convert  it  into  Light, 
and  cause  the  body  to  shine.  This  we  can  do  by  exposing  a 
piece  of  platinum  wire  to  heat  of  gradually  increasing  intensity. 
At  first  it  em'ts  only  obscure  rays  of  heat,  then  luminous  rays 
of  light  of  a  very  feeble  red  color,  then  those  of  a  bright  cherry 
red,  then  orange,  yellow,  white,  and  finally  an  intense  blue.  It 
has  b  'en  calculated  that  all  red  light  is  produced  by  a  temper- 
ature of  700°,  bright  red  900°,  full  red  heat  1000°,  yellow  1 100°, 
white  light  1400°  to  3280°.  Even  the  dull  >st  substances  may 
thus  be  made  to  emit  light  of  the  greatest  brilliancy  and  inten- 
sity. From  this  it  would  seem  that  Light  is  only  the  exceed- 

Show  how  the  diminution  of  temperature  in  the  atmosphere,  as  we  ascend,  may  be  ex- 
plained upo.i  the  mechanical  theory.— 263.  Show  how  heat  can  be  converted  into  light 


244  TH2    CONVERTIBILITY    OF    FORCES  __.,,< 

ingly  rapid  vibrations  of  the  same  ether,  which  when  vibrating 
more  slowly  produces  merely  the  effect  and  sensation  of  Heat. 
As  the^e  heat  vibrations  increase  in  rapidity  they  produce,  first 
that  kind  of  light  which  results  from  the  slowest  Light 
vibrations,  then  that  color  which  is  produced  by  vibrations  of  a 
more  rapid  character,  and  finally  blue  light,  which  has  been 
found  to  be  produced  by  the  most  rapid  vibrations,  and  to  be 
possessed  of  the  greatest  refrangibility.  On  the  other  hand, 
that  Light  may  be  converted  into  Heat,  seems  to  be  proved  by 
the  experiment  of  placing  cloths  of  different  colors  upon  the 
snow.  The  temperature  of  these  cloths  is  shown  by  the  depth 
to  which  the  snow  is  melted  beneath  them;  and  this  is  found  to 
be  precisely  the  order  in  which -they  absorb  the  light:  blade  de- 
stroys all  light  vibrations  and  it  is  found  to  be  healed  the  most 
and  sunk  the  most  deeply  in  the  snow;  next  comes  blue,  gr^en, 
purple,  red  and  yellow,  white  reflects  all  the  liglit,  and  conse- 
quently is  hca'ed  the  least  of  all  the  colors.  Light  can  also  be 
resolved  into  heat  through  the  medium  of  chemical  action. 
Heat  and  Light  are  therefore  produced  by  the  same  cause,  act- 
ing with  different  degrees  of  intensity,  and  we  naturally  pass, 
therefore,  from  the  study  of  radiant  Heat  to  that  of  radiant 
Light. 

261.  The  convertibility  of  the  Forces  which  act  upon  mat- 
ter into  each  other  and  their  indestructibility.  The  general 
conclusion  at  which  modern  science  has  arrived,  is  that  the  va- 
rious forms  of  force  which  act  upon  matter  are,  many  of 
them,  if  not  all,  capable  of  passing  into  each  other,  and  that  in 
all  cases  when  a  force  seems  to  be  destroyed,  it  is  not  really 
so,  but  simply  converted  into  another  variety  of  force  of 
equal  energy.  Force  is,  then,  believed  to  be  as  indestructible  as 
matter.  By  this  expression  it  is  not  meant  that  either  force  or 
matter  are  incapable  of  destruction,  but  simply,  that  in  fact,  as 
the  material  world  is  at  present  constituted,  neither  of  them  is 
destroyed  in  the  various  transmutations  which  they  undergo, 
but  are  merely  changed  from  one  form  to  another.  The  pri- 
mary form  of  force  which  is  selected  as  the  type  of  all  the  oth- 
ers is  mechanical  motion.  Into  this  all  the  others  are  capab'e 
of  being  resolved,  and  out  of  it,  most  of  them  can  be  again 
el' cited.  From  heat  may  be  obtained  light,  electricity,  chemi- 
cal action  and  motion;  from  light  may  be  obtained  chemical 

Show  that  light  may  be  converted  into  heat — 254.  What  is  the  general  concluFion  of 
modern  science  in  regard  to  the  convertibility  of  the  forces  that  act  on  mutter,  aiii  t-ieir 
indes  tr  uctibility . 


WHICH    ACT    UPON    MATTER.  245 

action  and  heat;  from  electricity,  heat,  light,  chemical  action, 
and  motion ;  from  chemical  action,  heat,  light,  electricity,  and 
motion  ;  from  motion  itself,  heat,  light,  electricity,  and  chemical 
action.  The  intimate  connection  of  Heat  and  Light,  c.nd  their 
mutual  convertibility,  will  be  seen  more  clearly  from  the  follow- 
ing chapter. 

264*.  There  is  an  Analogy  between  Sound,  and  Heat,  and 
Light.  It  is  well  known  that  sound  is  produced  by  vibrations 
imparted  to  the  air,  and  that  the  pitch  of  a  sound  depends  upon 
the  number  of  these  vibrations.  In  like  manner  it  is  thought 
that  heat  and  light  are  produced  by  the  vibrations  of  an  ex- 
tremely sensitive  ether  with  which  all  matter  is  peimeated. 
1  he  difference  between  the  vibrations  of  air  and  ether  consists 
in  the  greater  delicacy  and  elasticity  of  ether,  which  not  only 
admits  of  a  greater  rapidity  in  the  propagation  of  motion,  but 
also  of  an  immensely  greater  number  of  vibrations  per  second, 
\\  hich  require  to  be  counted  by  billions.  The  difference  there- 
fore between  sound,  heat,  and  light  is  chiefly  a  difference  in 
the  rale  of  vibration  of  the  respective  media  which  produce 
them. 

Again,  the  vibrations  communicated  to  air  are  also  imparted 
to  the  ether  by  which  it  is  permeated.  These  vibrations  at  first 
produce  only  the  phenomena  of  sound,  but  as  soon  as  they  exceed 
a  certain  number  per  second  the  phenomena  of  heat  begin  to 
manife  t  themselves,  and  should  these  vibrations  go  beyond  a 
certain  limit,  then  the  phenomena  of  light  make  their  appear- 
ance. Here  we  have  another  illustration  of  the  convertibility 
of  forces,  which  is  described  very  elegantly  by  Dove  as  follows  : 
"  In  the  middle  of  a  large  darkened  room  let  us  suppose  a  rod 
set  in  vibiatiou  and  connected  with  a  contrivance  for  continu- 
ally augmenting  the  speed  of  its  vibrations.  I  enter  the  room  at 
the  moment  when  the  rod  is  vibrating  four  times  in  a  second. 
Neither  eye  nor  ear  tell  me  of  the  presence  of  the  rod,  o.Jy 
the  hand  which  feels  the  strokes  when  brought  within  their 
reach.  The  vibrations  become  more  rapid,  till  when  they 
reach  the  number  of  thirty-two  in  a  second,  a  deep  hum  strikes 
my  e;ir.  The  tor.e  rises  continually  in  pitch,  and  passes  through 
all  the  intervening  grades  up  to  the  highest,  the  shrillest  note,  then 
ail  j-inks  again  into  the  former  grave-like  silence.  "While  full  of 
astonishment  at  what  I  have  heard,  I  feel  suddenly  (by  the  in- 
creased velocity  of  the  vibrating  rod)  an  agreeable  warmth,  ag 
from  a  fire,  diffusing  itself  from  the  spot  whence  the  sound  had 
proceeded.  S.ill  all  is  dark.  The  vibrations  increase  in  ra.- 


246  THE    NATURE    OF   LIGHT. 

pidity,  and  a  faint  red  light  begins  to  glimmer ;  it  'gradually 
brightens  till  the  rod  assumes  a  vivid  red  glow,  then  it  turns 
to  yellow,  and  changes  through  the  whole  range  of  colors  up 
to  violet,  when  all  again  is  swallowed  up  in  night.  Thus  na- 
lure  speaks  to  the  different  senses  in  succession,  at  first  a  gentle 
word,  audible  only  in  immediate  proximity,  then  a  louder  call 
from  an  ever  increa-ing  distance,  till  finally  her  voice  is  borne 
on  the  wings  of  light  from  regions  of  immeasurable  space." 


CHAPTER  III. 

THE    SECOND    CHEMICAL    AGENT: LIGHT. 

THE    NATURE    OF   LIGHT;    SOURCES;    REFLECTION;    REFRACTION;    SOLAR    SPEC- 
TRUM;   SPECTRUM    ANALYSIS',    EFFECT   OF   LIGHT    ON    PLANTS;    CHEMICAL 
EFFECTS  OF  LIGHT}  PHOTOGRAPHY;   RELATIONS  OF  LIGHT  AND  HEAT. 

263.  The  nature  of  Light,  The  second  of  the  great  Im- 
ponderable Agents  controlling  the  action  of  Affinity,  and  play- 
ing an  important  part  in  many  chemical  phenomena,  is  Light. 
There  are  two  hypotheses  in  regard  to  the  nature  of  light  cor- 
responding with  those  which  have  been  explained  in  regard  to 
the  nature  of  heat.  According  to  the  first  of  these,  light  is  a 
subtile  material  fluid,  which  is  thrown  off  by  all  luminous  bodies, 
composed  of  particles  inconceivably  minute,  and  moving  with 
immense  velocity.  These  particles  falling  on  different  substan- 
ces are  reflected,  transmitted,  or  absorbed,  and  when  they 
strike  upon  the  optic  nerve,  produce  the  sensation  of  light. 
The  second  hypothesis  supposes  that  light  is  the  result  of  undu- 
lation, produced  in  an  exceedingly  rare  and  subtile  medium, 
pervading  all  space,  and  filling  the  interstices  of  all  forms  of 
mat  er.  This  medium  is  not  light  itself,  but  it  can  be  thrown 
into  the  vibrations  which  constitute  light  by  impulses  communi- 
cated to  it  by  all  luminous  objects.  The  latter  is  the  theory 
now  generally  received,  as  it  affords  the  most  complete  explana- 
tion of  all  the  phenomena  of  light.  It  is  strongly  supported  by 
'the  analogy  of  sound,  which,  as  is  well  known,  is  produced  by 
the  undulations  of  the  air,  and  is  in  like  manner  susceptible  of 
transmission,  reflection,  and  absorption  ;  it  also  corresponds  with 

235.  What  Is  the  second  imponderable  ?     IIow  many  theories  are  there  in  regard  to  the 
»ature  of  light  ?    State  the  material  theory.     The  undulatory  theory. 


SOURCES    OF    LIGHT. THE    SUN.  247 

.the  undulatory  theory  of  heat  already  explained,  and  now  be- 
ginning to  be  generally  received. 

265.  The  sources  of  liight.-Solar  Xtigiit.  The  first  and 
most  important  source  of  light,  is  the  sun  and  the  heavenly 
bodies.  The  origin  of  the  light  of  the  sun  and  the  stars  isjm- 
known,  but  it  is  generally  supposed  that  the  inflammable  mat- 
ter which  appears  to  surround  the  sun  is  gaseous  in  its  charac- 
ter, because  the  light  which  it  emits  is  the  same  as  that  which 
proceeds  from  gaseous,  inflammable  substances,  and  does  not 
afford  any  trace  of  polarization  by  the  instruments  intended  to 
detect  it.  Astronomical  investigations  have  rendered  it  proba- 
ble that  the  sun  consists  of  two  parts,  a  central  mass,  emilting 
light  of  great  brilliancy,  and  an  external  luminous  atmosphere, 
also  emitting  light,  and  called  a  photosphere.  This  view  of  the 
constitution  of  the  sun  is  supported  by  the  recent  discoveries 
con  lected  with  spectrum  analysis. 

267.  Ignition  of  Solids  a  source  of  Light.  Whenever  any 
solid  body  is  raised  to  a  temperature  of  900°,  or  1000°,  it  be- 
gins to  emit  light,  and  becomes  luminous,  or  incandescent. 
Even  gaseous  matter,  if  heated  to  2000°,  becomes  feebly  lumi- 
nous. ,  If  any  solid  matter  be  introduced  into  a  current  of  gas 
at  this  high  temperature,  the  brightness  of  the  light  is  greatly 
increased,  and  it  is  upon  the  ignition  of  solid  matter  in  the 
interior  of  currents  of  intensely  heated  gas,  that  all  processes 
of  artificial  illumination  in  common  use,  depend.  In  the  case  of 
ilLnninating  ga^,  kerosene,  candles,  and  oil,  the  solid  sub- 
stance emitting  the  light,  is  carbon  in  a  state  of  intense  igni- 
tion, precipitated  from  the  gas  in  which  it  previously  existed  in 
combination  with  hydrogen.  This  very  curious  and  beautiful 
process,  on  which  so  much  of  the  comfort  and  enjoyment  of  man 
depend^,  will  be  more  particularly  described  hereafter,  One  of 
the  most  remarkable  in-tances  of  the  production  of  light  in  this 
manner  is  seen  in  the  case  of  the  Drummond  light,  in  which  a 
jet  of  mixed  oxygen  and  hydrogen  is  directed  upon  a  pi;  ce  of 
solid  lime.  The  gases  burning  alone  produce  a  flame  which  is 
hardly  perceptible,  but  the  moment  the  lime  is  introduced,  the 
brilliancy  of  the  light  becomes  at  once  too  great  for  the  eye  to 
bear.  Even  a  piece  of  platinum,  or  of  china,  introduced  into 

2-58,  What  is  the  first  source  of  light  ?  Why  is  the  light  of  the  sun  and  stars  supposed 
to  be  of  g  iseous  origin  ?  What  is  supposed  to  bo  the  constitution  of  the  sun  ,'—267,  \Vu.it 
is  the  second  source  of  light  ?  How  can  solid  matter  be  mado  to  emit  light  ?  On  what  do 
all  processes  of  artificial  light  in  common  u'e  depend?  What  is  the  ignited  solid  sub- 
Btance  which,  emits  light  in  the  burning  of  i.luminating  gas  and  candles?  Explain  tUt) 
Drummond  light.  Does  the  ignited  solid  in  tills  c.^o  undergo  aay  change? 


248  IGNITION    OF    SOLIDS. ELECTRICITY. 

this  flame,  or  any  other  solid  substance,  will  instantly  begin  to 
emit  light.  In  all  these  cases  the  solid  itself  undergoes  no 
change,  and  remains  unconsumed.  The  color  of  the  light  va- 
ries with  the  intensity  of  the  heat ;  when  first  perceptible,  it  is 
of  a  dull  red,  and  gradually  passes  into  orange,  yeilow,  white, 
and  violet.  The  temperature  at  which  bodies  begin  to  emit  red 
light  in  the  dark,  is  about  700°,  but  in  broad  daylight,  solid 
matter  does  not  become  incandescent  until  heated  to  1000°. 
Platinum  begins  to  emit  light  in  the  dark,  at  977°.  If  platinum, 
brass,  antimony,  gas-carbon,  porcelain,  black-lead,  copper,  and 
palladium,  be  introduced  into  a  clean  gun-barrel,  which  is  then 
raised  to  a  dull  red  heat,  they  are  found,  on  looking  into  the 
barrel,  to  emit  red  light  at  the  same  moment,  showing  that  they 
all  require  nearly  the  same  temperature  to  make  them  incan- 
descent. Chalk  and  marble,  under  the  same  circumstance-, 
require  a  lower  temperature,  and  begin  to  emit  light  before  the 
gun-barrel  is  red-hot. 

268.  Electricity  a  source  of  Light.  This  is  a  powerful 
source  of  light,  as  may  be  seen  in  the  case  of  the  sparks  pro- 
duced by  the  ord'nary  electric  machine,  and  also  by  the  excess- 
ive brightness  of  a  flash  of  lightning.  The  galvanic  battery 
produces  a  steady  and  permanent  light,  too  bright  for  the  un- 
protected eye  to  bear,  if  the  wires  from  the  two  poles  are  tipped 
with  charcoal,  and  brought  near  enough  to  each  other  for  the 
electric  current  to  pass.  Attempts  have  been  made  to  employ 
this  light  in  light-houses,  but  with  indifferent  success.  In  the 
galvanic  battery,  chemical  action  is  the  source  of  the  electrical 
current ;  but  this  may  also  be  produced  by  the  revolution  of 
wound  armatures  before  the  poles  of  powerful  magnets,  and  if 
this  current  be  allowed  to  pass  through  charcoal  points,  light  of 
equal  in-ensity  to  that  of  the  galvanic  battery  may  be  obtained. 
The  motion  required  may  be  generated  by  a  small  steam  engine. 
This  is  the  form  in  which  electricity  is  now  chiefly  used  for  the 
production  of  artificial  light.  Here  we  have  a  striking  instance 
of  the  conversion  of  forces ;  heat  produces  motion ;  motion  is 
resolved  into  electricity,  and  this  electricity  into  heat  and  light. 
The  electric  light  from  the  battery  is  frequently  substituted  for 
the  sun,  in  optical  experiments,  on  account  of  its  excessive 
brightness. 

What  is  the  temperature  at  which  red  light  in  the  dark  is  emitted  ?  In  broad  day- 
light ?  Do  all  bodies  require  nearly  the  same  temperature  to  render  them  incandescent? 
—268.  What  is  the  third  source  of  light  ?  What  is  said  of  the  light  produced  by  the 
galvanic  battery?  To  what  purpose  has  it  been  applied?  By  what  other  means  has 
light  of  equal  intensity  been  produced  ?  Can  motion  be  converted  into  light  ?  What 
r  illustration  does  this  afford  of  the  conversion  of  forces  ? 


PHOSPHORESCENCE. CRYSTALLIZATION.  249 

269-  Exposure  to  the  sun's  rays,  and  to  electricity,  a 
source  of  Slight.  There  are  some  substances,  like  the  diamond, 
and  other  minerals,  which,  after  being  exposed  to  the  sun's  rays 
for  some  time,  appear  luminous  when  carried  into  a  dark  place. 
Thi>  property  of  emitting  light  without  the  application  of  an 
eleva'ed  artificial  temperature,  is  called  phosphorescence.  Fluor 
spar,  the  diamond,  and  white  marble,  acquire  phosphorescence, 
on  the  discharge  through  them  of  a  succession  of  electric  sparks. 
Ag;iin,  if  fluor  spar  be  heated  quite  hot,  it  will  become  phos- 
phorescent, and  emit  a  beautiful  blue  light. 

270.  Decaying-  animal  and  vegetable  matter  a  source  of 
Light.    Sea  fish,  and  especially  the  herring  and  mackerel,  become 
phosphorescent  shortly  after  death.     By  placing  such  fish  in  weak 
saline  solutions,  such  as  sea  salt,  these  solutions  become  lumi- 
nous, and  this  appearance  will  continue  for  some  time.     In  like 
manner,  certain  species  of  wood,  in  a  state  of  decomposition, 
become  phosphorescent,  and  shine  with  considerable  brilliancy 
in  the  dark.     In  all  these  cases  the  light  ceases  to  be  given 
forth  if  the  temperature  be  reduced  below  32°.     The  light  is 
probably  due  to  a  species  of  slow  combustion,  produced  by  the 
combination  of  the  substance  in  question  with  the  oxygen  of 
the  air.     Phosphorus,  a  simple  sub.  tance  extracted  from  bones, 
also  emits  quite  a  brilliant  light,  when  exposed  to  the  air,  on 
account  of  its  rapid  union  with  oxygen,  and  as  this  substance 
exists  to  a  limited  degree  in  all  animal  and  vegetable  matter,  it 
is.  not  unlikely  that  their  phosphorescence  may  be  due  to  this 
cause. 

271.  Luminous  animals  a  source  of  Ztight.    The  glow-worm 
and  the  fire-fly  have  the  power  of  giving  out  light,  and  in  tropical 
climates  there  are  numerous  insects  which,  on  being  irritated, 
emit  sufficient  light  to  allow  of  reading.     The  waters  of  the 
ocean,  in  tropical  latitudes,   emit  a  beautiful    phosphorescent 
light,  on  ag'tation,  which  is  thought  to  be  due  to  the  presence 
of  minute  animalcule-.     Two  of  these  animalcules  placed  in  a 
bottle  of  water,  have  been  known  to  diffuse  a  luminous  influence 
through  the  whole  mass. 

272.  Crystallization  a  source  of  Idg-ht.      If  sulphate    of 
sod  i,  and  a  few  other  salts  that  have  been  fused  by  the  action 
of  fire,  be  dissolved  in  water,  and  crystallized,  the  formation 

2  "9.  What  is  the  fourth  source  of  light?  What  is  phosphorescence?  How  do  fluor 
spiv,  tlie  di.m.ond,  and  white  marble,  acquire  phosphorescence ? — 270.  What  is  the  fifth 
sou  re  e  of  li<x  it .'  To  what  is  this  light  probably  duo?  Whnt  i-i  said  of  phosphorus  as  a 
so-ine  ofHg'it?— 271  U'hst  i<  the  sixth  source  of  light?  Give  iilu.str.itioas. — 272  \Viiat 
is  the  sevonta  source  of  liglit .'  Give  illustrations.  , 


250  THE    REFLECTION    OF    LIGHT. 

and  separation  of  each  crystal  will  bo  attended  by  a  flash  of 
light.  The  same  result  is  produced  if  transparent  arsenious 
acid  is  dissolved  in  hot  chloro-hydric  acid,  and  allowed  to  crys- 
tallize ;  if  the  process  be  watched  in  a  darkened  room,  a  faint 
flash  of  light  will  be  seen  to  accompany  the  deposition  of  each 
crystal.  The  cause  of  this  light  is  not  known. 

273.  The  reflection  of  Light.  Light,  whatever  be  the 
source  from  which  it  emanates,  proceeds  in  straight  lines,  and 
these  rad  ate  from  the  luminous  centre  equally  in  all  directions. 
The^e  fine  radiations  are  called  rays,  and  a  collected  bundle  of 
them  is  called  a  beam  of  light.  The  intensity  of  light  d'min- 
ishe*  according  to  the  square  of  the  distance  from  the  luminous 
centre ;  so  that  a  body  receives  one-quarter  the  light  at  a  dis- 
tance of  two  feet  from  the  source  of  light,  that  it  did  at  the 
distance  of  one  foot.  When  these  rays  fall  upon  the  surface  of 
solid  bodies  they  are  reflected,  absorbed,  transmitted,  and  re- 
fracted, in  the  same  manner  as  rays  of  heat  under  similar  cir- 
cum  tances.  The  law  of  reflection  is,  that  the  angle  which  the 
in  -ident  ray  makes  with  a  perpendicular  at  the  point  of  contact 
with  the  reflecting  surface,  is  equal  to  the  angle  which  the  re- 
flected ray  makes  with  the  same  perpendicular.  The  phenomena 
of  the  reflection  of  light  from  mirrors,  are  the  same  as  for  the 
reflection  of  heat,  §  73.  There  are  different  kinds  of  light,  dis- 
tinguished from  each  other  by  color,  just  as  there  are  different 
kinds  of  heat,  distinguished  from  each  other  by  temperature ; 
and  when  a  beam  of  common  light  falls  upon  a  solid  body,  pome 
of  the  kinds  of  light  of  which  it  is  composed  may  be  absorbed, 
and  some  reflected.  It  is  by  this  absorption  of  certain  rays,  and 
the  reflection  of  others,  that  the  colors  of  bodies  are  produced ; 
the  color  of  the  body  in  question  being  that  of  the  rays  which 
are  reflected.  If  all  the  rays  are  absorbed,  except  the  red,  the 
body  will  appear  to  be  of  a  red  color ;  if  all  are  absorbed  ex- 
cept the  yellow  and  the  blue,  the  body  will  seem  to  be  of  a 
green  co^or,  green  being  produced  by  a  mixture  of  yellow  and 
blr.e.  There  are  certain  bodies  which  transmit  light  freely, 
without  ab  orption,  and  allow  objects  to  be  seen  through  them  ; 
these  are  called  transparent :  those  which  do  not  allow  the  light 
to  pass  through  them  are  called  opaque.  There  are  no  sub- 
stances, however,  which  are  perfectly  transparent.  The  purest 

273.  In  what  direction  do  rays  of  light  proceed  ?  What  becomes  of  these  rays  when 
they  f.ill  0:1  other  substances?  What  is  the  law  of  reflection?  How  does  the  reflection 
of  ugfit  compare  with  that  of  heat?  Explain  the  colors  of  bodies.  What  are  transpa- 
rent, anl  wliat  opaque  bodies?  Are  there  any  substances  perfectly  transparent  or 
opaque  ? 


THE    REFRACTION    AND  251 

afmosphere,  and  the  clearest  glass,  arrest  a  portion  of  the  light. 
It  is  estimated  that  not  more  than  ^V^  part  of  the  light  of  the  sun's 
beams  reach  the  earth,  the  remainder  being  absorbed.  On  the 
other  hand,  there  are  no  bodies  which  are  perfectly  opaque ; 
gold,  one  of  the  densest  of  the  metals,  may  be  hammered  into 
very  thin  leaves,  which  transmit  a  green  light,  if  the  metal  be 
pure  gold,  and  purple,  if  alloyed  with  silver. 

274.  The  refraction  of  Light.  If  a  ray  of  light  fall  per- 
pendicularly upon  any  transparent  medium,  it  will  continue  on 
its  course  without  any  deviation ;  but  if  it  fall  obliquely,  it  will 
be  bent  more  or  less  out  of  its  original  course.  This  sudden 
bending  of  a  ray  of  light  is  called  refraction.  The  refracted 
ray  passes  on  in  its  new  direction,  through  the  refracting  medium, 
in  a  straight  line;  but  on  issuing  again  upon  the  opposite  side, 
it  is  refracted  a  second  time  in  a  contrary  direction,  and  is 
restored  to  a  course  parallel  to  that  which  it  had  at  first,  pro- 
vided the  two  refracting  surfaces  are  exactly  parallel.  Refrac- 
tion always  takes  place  when  rays  of  light  pass  from  a  rarer  to 
a  denser  medium,  or  from  a  denser  into  a  rarer  medium,  as  from 
air  into  glass  or  water,  and  from  g]ass  or  water  into  air.  This 
is  illustrated  in  Fig.  100,  where  s  A  represents  the  incident  ray, 

and  N  M  the  refracting  medium. 
As  soon  as  the  ray  of  light  passes 
out  of  the  air  into  the  p'ate  of 
glass  at  A,  it  is  bent  out  of  its 
course  towards  D  ;  and  aga'n, 
when  it  passes  from  the  den  er 
medium  of  the  glass,  into  the 
rarer  medium  of  the  air,  it  is  re- 
fracted in  the  opposite  direction, 
and  takes  the  direction,  D  B,  par- 
Refmction  of  Light.  allel  to  its  original  course.  Iii 

general,  the  den-er  a  sub:tance 

is,  the  greater  is  the  refraction  which  it  produces  in  a  ray  of 
light.  But  this  is  far  from  being  universally  true,  for  ether, 
alcohol,  and  olive  oil,  which  are  lighter  than  water,  have  a  higher 
refractive  power.  Observation  has  shown  that  inflammable,  or 
combustible  bodies,  such  as  the  diamond,  phosphorus,  sulphur, 
amber,  camphor,  olive  and  other  oils,  have  a  refractive  power 
from  two  to  seven  times  greater  than  that  of  incombustible  sub- 

274    What  is  meant  by  the  refraction  of  light?     In  what  direction  does  the  light  pass 
through  the  refracting  medium?     Describe  Fig.  100.     What  effect  has  density  upon  re- 
fractive power  ?    What  has  been  noticed  in  regard  to  combustible  substances? 
11 


252  DOUBLE    REFRACTION    OF    LIGHT. 

stances  of  equal  density.  The  laws  and  phenomena  of  refrac- 
tion are  among  the  most  interesting  and  important  of  all  (ho.ce 
connected  with  the  subject  of  light,  and  upon  them  depends  the 
operation  of  the  microscope,  telescope,  and  many  other  optical 
instruments.  Their  consideration,  however,  belongs  more  par- 
ticularly to  Natural  Philosophy,  and  the  student  is  referred,  for 
their  full  explanation,  to  some  extended  treatise  upon  Optics. 

275.  Double  refraction  and  polarization  of  Light.  Light  is 
not  only  susceptible  of  simple,  but  also  of  double  refraction,  as 
is  the  case  with  rays  of  heat.  If  a  ray  of  light  be  allowed  to 
fall  at  an  oblique  angle  upon  a  rhombohedi  al  crystal  of  Iceland 
spar,  Fig.  101,  it  will  be  separated  into  two  reft  acted  rays,  one 

of  which,  o,  will  follow  the  ordi- 
nary  law  of  refraction ;  the  other, 
E,  pursues  a  totally  different  di- 
rection, and  in  a  different  plane. 
The  former  is  called  the  ordi- 
nary, the  latter  the  extraordi- 
nary, ray.  Light  that  has  been 
doubly  refracted  is  found  to  have 
undeigone  a  remarkable  rncdifi- 
cat'on,  arid  is  no  longer  capable 
of  reflection,  refraction,  or  trans- 

Doubie  Refraction  of  Li^kt.  mission    in    the    same    manner 

as    before.      Each    ray   on 

'  emerging,  has  acquired  new  properties.  The  rays,  in  fact, 
appear  to  have  acquired  sides,  and  to  have  new  relations  to  cer- 
tain planes  within  the  crystal ;  euch  rays  are  ga'd  to  le  ro7ar- 
ized.  Light  may  be  polarized  by  reflection,  and  ako  by  trans- 
mission through  bundles  of  plates,  as  well  as  by  certain  crystals. 
Polarized  light  is  possessed  of  many  peculiarities,  which  have 
been  applied  to  some  important  practical  purposes.  A  portion 
of  all  reflected  light  is  polarized,  and  thus  the  astronomer  can 
ascertain  whether  the  light  proceeding  from  a  heavenly  tody 
had  its  origin  in  the  body  itself,  or  has  been  derived  from  feme 
o'her  source.  Light  proceeding  from  incandescent  bodies,  such 
as  hot  iron,  glass,  and  various  liquids  under  a  certain  angle,  is 
polarized ;  and  from  a  gaseous  substance,  such  as  illuminating 
gas,  is  in  its  unpolaiized  condition.  On  applying  this  principle 

275.  What  is  meant  by  double  refraction?  By  polarization?  Are  there  any  otl.er 
means  by  which  light  can  be  polarized  ?  What  peculiarity  is  possessed  by  all  reflected 
light?  What  is  the  differerce  between  light  proceeding  from  ignited  solid  bodk*  End 
ignited  gases?  What  application  has  Arago  made  of  this  principle  to  the  light  ot  the 


THE    DECOMPOSITION    OF    LIGHT  253 

to  the  sun,  Arago  is  said  to  have  discovered  that  the  light  which  it 
emits  is  of  gaseous  origin.  On  transmitting  polarized  light 
through  transparent  media,  whose  structure  is  not  perfectly 
homogeneous  and  then  allowing  the  light  to  be  reflected  to  the 
eye  of  the  observer,  at  an  angle  of  56°,  the  most  brilliant  col- 
ors will  appear.  From  the  production  of  these  colors,  we  can 
infer  the  want  of  homogeneity  in  the  transparent  medium ;  and 
by  an  extension  of  observations  of  this  kind,  instruments  have 
been  constructed  by  which  a  quantity  of  crystallized  matter  ex- 
iting in  any  solution  may  be  ascertained,  too  minute  for  the 
power  of  ordinary  chemical  analysis  to  detect.  This  has  been 
practically  applied  in  the  manufacture  of  sugar,  and  to  the  de- 
termination of  the  progress  of  diseases  in  the  human  body. 
For  details,  in  reference  to  this  interesting,  but  difficult  subject, 
reference  must  be  made  to  some  treatise  on  Optics. 

275.    The  compound  nature  of  Solar  Iiigrht.— The  Illumina- 
ting- Rays.    A  beam  of  solar  light  does  not  consist  of  one  sin- 
g'e  kind  of  light,  but  of  several,  possessed  of  different  colors 
when  separated,  but  when  united,  produc'ng  upon  the  eye  the 
impression  of  white  light.     These  different  kinds  of  light  are 
possessed  of  Different  refrangibility,   and   consequently,   when 
made  to  pass  through  the  same  refractive 
Fig.  102.  medium,  they  are  not  all  bent  to  the  same 

extent  from  their  original  course.  By  this 
unequal  refraction,  they  are  separated  from 
each  other,  and  each  can  be  made  to  exhibit 
its  own  proper  color.  Sir  Isaac  Newton  was 
the  discoverer  of  the  compound  nature  of 
white  light,  and  he  employed  for  this  pur- 
pose a  solid  piece  of  glass,  of  triangular 

shape,  known  under  the  name  of  the  prism, 

Prism.  Fig.    102.     Sometimes   the   prism  is   made 

hollow,  and  filled  with  water,  or  rome  other 
liquid.  On  placing  the  prism  in  such  a  position  that  one  of  its 
fa:>es  may  be  horizontal,  as  at  A,  Fig.  103,  and  allowing  a  beam 
of  sunlight,  admitted  through  a  very  small  circular  aperture,  to 
fall  at  an  oblique'  angle  upon  one  of  the  other  fares,  the 
beam  of  sunlight,  in  passing  through  the  prism,  will  be  re- 
fracted twice,  once  at  its  entrance,  and  again  at  its  emerg- 

Wiiat  e!Tect  takes  place  when  polarized  light  is  transmitted  through  bodies  whoso  struc- 
ture is  not  perfectly  homogeneous?  What  applications  have  been  made  of  thefe  prin- 
ciples?— 276.  How  can  the  compound  nature  of  solar  light  be  shown?  In  what  respects 
do  th«  different  kin. Is  of  lig'it  differ  f'-om  each  other?  Who  discovered  the  compound 
nature  cf  lijjht?  What  is. a  prism  ?  IIow  can  it  Le  use<4  to  decompose  light? 


'254 


BY    THE 


The  Decomposition  of  Light. 


FiS-  103-  ence   from    the 

prism,  and  1  he  rays 
of  which  it  is  com- 
posed being  bent 
from  their  original 
course  unequally, 
will  be  separated 
from  each  other, 
and  caused  to  di- 
verge. In  corse- 

qUCIlCC    of  this    di- 

vergence,  the  dif- 
ferently colored  rays  will  become  distinct,  and  be  beauti- 
fully displayed  if  a  screen  be  placed  to  receive  lh<  m.  The 
colored  rays  are  seven  in  number,  and  are  always  arranged 
in  the  same  order.  The  oblong  spot  of  colored  light  which  they 
form  is  called  the  solar  spectrum.  At  the  upper  end  of  the 
spectrum,  where  the  most  refracted  rays  fall,  the  color  is  violet  ; 
then  comes  the  indigo  ray,  the  blue,  green,  yellow,  orange,  and 
red,  which  is  refracted  the  least.  The  shape  of  the  spectnm 
depends  upon  the  shape  of  the  aperture  ;  if  this  be  circular,  th» 
spectrum  will  be  bounded  laterally  by  vertical  straight  lines, 
and  at  the  ends  by  semicircles  ;  its  breadth  is  always  equal  to 
the  diameter  of  the  aperture  ;  its  length  varies  with  the  refract- 
ing angle  of  the  prism,  and  the  substance  of  which  it  is  made. 
As  in  the  original  beam  of  white  light,  the  various  colored  rays 
are  all  superimposed,  it  follows  that  if  the  spectrum  formed  be 
only  slightly  elongated,  in  consequence  of  the  feeble  refractive 
power  of  the  prism,  the  different  colors  will  overlap  each  other, 
be  more  or  less  blended,  and  none  of  them  will  present  a  clear 
and  decided  tint.  In  order  to  increase  the  brilliancy  of  the 
spectrum,  it  is  necessary  that  the  aperture  through  \\hich  the 
light  is  admitted  should  be  very  small,  in  order  to  obtain  the 
finest  possible  beam  of  light,  and  then  that  the  screen  should  le 
p'aced  at  a  considerable  distance  from  the  prism,  so  that  the 
rays  may  not  strike  it  until  they  have  widely  diverged,  and  be- 
come completely  separated  from  each  other  ;  in  this  manner  a 
spectrum  may  be  obtained  in  which  the  different  rays  will  dis- 
play clear  and  decided  tints  of  great  brilliancy  and  beauty. 
The  most  effective  mode  of  producing  this  result  is  to  form  a 


Describe  the  so!ar  spectrum.  What  is  its  shape?  How  can  it  be  displayed  to  the 
best  advantage?  How  may  the  brilliant  line  of  colored  light  produced  by  this  means 
be  widened  ? 


THE    SOLAR    SPECTRUM.  255 

minute  image  of  the  sun  by  means  of  a  convex  lens,  and  allow 
the  light  which  proceeds  from  it  to  fall  upon  a  screen,  pierced 
with  a  very  small  aperture.  The  light  which  passes  through 
this  aperture  may  be  considered  as  emanating  nearly  from  a 
physical  point,  and  the  overlapping  of  the  different  colors  is 
almost  entirely  prevented.  Another  cause  of  the  imperfect 
separation  of  the  different  rays  exists  in  the  prism  itself.  Ordi- 
nary prisms  are  full  of  striae,  by  which  the  light  is  irregularly 
refracted,  and  the  different  colors  intermingled.  This  difficulty 
may  be  overcome  to  a  certain  extent  by  transmitting  the  rays 
as  near  the  edge  as  possible.  The  effect  of  this  reduclion  in 
the  diameter  of  the  aperture  will  be  to  diminish  the  width  of 
the  spectrum,  and  reduce  it  to  the  form  of  a  mere  line  of  light 
of  the  most  brilliant  colors.  In  order  to  give  breadth  to  this 
line  it  is  necessary  to  convert  the  circular  aperture  into  an  ex- 
tremely narrow  slit,  formed  by  perfectly  parallel  knife  edgas, 
only  a  very  small  fraction  of  an  inch  apart ;  a  spectrum  will 
thus  be  formed,  horizontal  and  rectangular,  having  its  upper 
edges,  as  well  as  its  sides,  parallel.  This  arrangement  is  the 
one  best  adapted  for  making  accurate  observations  upon  the 
spectrum.  The  colored  spaces  do  not  occupy  an  equal  extent 
in  the  spectrum  ;  the  violet  is  the  most  extended,  and  the  orange 
the  least ;  if  the  prism  be  of  flint  glass,  and  the  spectrum  be 
divided  into  three  hundred  and  sixty  equal  parts,  it  is  found 
tint  the  red  rays  occupy  forty-five  of  these  parts,  the  orange 
twenty-seven,  the  yellow  forty-eight,  the  green  sixty,  the  indigo 
forty,  and  the  violet  eighty.  If  the  screen  on  which  the  spec- 
trum is  formed  be  perforated  opposite  any  of  the  colors,  as  the 
violet,  for  example,  a  small  beam  of  pure  violet  light  will  pass 
through,  which  may  be  examined  separate  from  the  others.  If 
this  beam  of  violet  l:ght  be  allowed  to  fall  on  a  second  prism, 
and  its  image  received  on  a  second  screen,  it  undergo; -s  no 
decomposition  into  light  of  various  colors,  but  simply  produces 
a  spot  of  violet  light,  of  the  same  shape  as  the  incident  bcnim. 
This  beam  may  be  again  and  a^ain  refracted  by  prism  =>  and 
leases,  but  it  will  undergo  no  further  change.  The  same  i-5 
true  of  all  the  colors.  Hence  it  appears  that  the  different 
rays  of  the  spectrum  are  incapable  of  further  separation  in  o 
rays  of  different  colors,  by  subsequent  refraction,  and  that 

What  will  he  the  shnpe  of  the  spectrum  formed  by  knife  edges  ?  Bo  the  different  colors 
occupy  the  same  space  in  the  solar  spectrum  ?  What  is  the  proportion?  Show  that  the 
duU-rent  colors  are  not  susceptible  of  further  decomposition.  Are  the  colors  confined  to 
one  part  of  the  spectrum  ?  • 


256  THE    HEAT    RAYS    OF 

the  solar  spectrum  gives  us  the  ultimate  analysis  of  white 
light.  From  these  and  other  experiments,  Sir  Isaac  Newton 
in  erred  that  white  light  is  composed  of  seven  co'orific  rajs; 
later  experiments  have  led  to  the  opinion  that  the  seven  colors 
of  the  spectrum  are  occas:oned  not  by  seven,  but  by  three 
simple  or  primary " rays,  viz.,  blue,  yellow  and  red.  These 
rays  are  concentrated  at  those  points  in  the  spectrum  where 
each  of  these  colors  appears  the  brightest,  but  each  color  is  in 
reality  spread  over  the  whole  spectrum,  forming,  with  the 
others,  a  variety  of  mixtures, — red  and  yellow  producing  the 
orange;  yellow  and  blue  the  green;  red  ard  blue,  with  a  liltle 
yellow,  the  violet.  The  prismatic  colors  also  differ  in  their  illu- 
minating power ;  the  orange  illuminates  in  a  higher  degree  than 
the  red,  the  yellow  than  the  orange.  The  maximum  of  illumi- 
nation lies  in  the  brightest  yellow,  or  the  palest  green  ;  tej  ond 
the  full  deep  green,  the  illuminating  power  sensibly  dimini.-.hes; 
the  blue  is  nearly  equal  to  the  red,  the  indigo  is  inferior  to  lie 
blue,  and  the  violet  is  the  lowest  on  the  scale.  If  the  ftvcn 
colors  of  the  spectrum  be  received  upon  seven  distinct  minors, 
so  arranged  as  to  reflect  them  all  to  one  point,  the  orig  nal  white 
light  of  the  solar  beam  will  be  reproduced. 

277.  The  number  cf  vibrations  required  to  produce  t he  dif- 
ferent colors  of  the  solar  spectrum.     According  to  the  undula- 
toiy  theory  of  light,  the  average  length  of  a  wave  in  white  light 
is  estimated  at  S-O^OTT  °f  an  mcn  5  m  re^  ngnt>  at  34^00  °f  an 
inch;  in  violet,  at  s^o<7  °f  an  mcn-     The  nrmber  of  vibia- 
t'.ons  in  white  light  is  estimated  at  500,000,000,000,000  per 
second;    in  red  light,  at  482,000,000,000,000;    and  in  viokt 
light,  at  707,000,000,000,000. 

278.  The  heat  rays  of  the  solar  beam.     Besides  the  different 
kinds  of  light  of  which  the  sunbeam  consists,  it  also  contains 
rays  of  heat,  and  heat  of  different  kinds.     The.^e  rays  of  heat 
are  distributed  through  the  spectrum,  and  are  not  com  entiat<  d 
at  one  point ;  consequently,  they  possess  different  refrangibili- 
ties,  and  are  distinguished  from  each  other  by  this  property. 
If  these  rays  of  heat  were  exactly  similar,  they  would  be  equal 
in  refrangibility,  and  be  all  collected  at  one  point,  after  passing 
through  the  prism.     They  not  only  differ  in  refrangibility,  but 
also  in  heating  intensity,  in  the  same  manner  as  the  rays  of 

According  to  later  experiments,  of  how  many  colors  is  the  solar  spectrum  thought  to 
consist?  Where  is  the  point  of  maximum  illumination  situated? — 277.  What  is  the 
length  of  a  wave  in  white  light?  In  red?  In  violet?  What  are  the  num  her 'of  vi)-ra 
tioiis  in,white  light?  In  red?  Tn  violet?— 278.  Show  that  there  are  different  kinds  of 
rays  of  heat  in  the  solar  beam. 


THE    SOLAR    BEAM.  257 

lio-ht  differ  in  illuminating  power.  This  fact  was  first  observed 
by  Sir  W.  Herschel,  who  observed  that  in  viewing  the  sun  with 
laro-e  telescopes,  through  differently  colored  glasses,  he  some- 
times felt  a  strong  sensation  of  heat,  with  little  light ;  and  at 
other  times  he  had  a  strong  light,  with  little  heat.  His  experi- 
ments were  made  by  transmitting  a  solar  beam  through  a 
prism,  receiving  the  spectrum  on  a  table,  and  placing  the  bulb 
of  a  very  delicate  thermometer  in  different  parts  of  if.  The 
thermometer  was  found  to  stand  at  different  points  in  tlie  differ- 
ent rays;  thus,  if  in  the  blue  rays,  it  marked  56°;  on  moving 
it  down  to  the  yellow  rays,  the  instrument  indicated  a  tempcra- 
ture  of  62° ;  while  at  the  lower  end  of  the  spectrum,  at  the 
extremity  of  the  red  rays,  the  temperature  was  found  to 
be  as  high  as  79°,  i.  e.,  23°  higher  than  in  the  blue  rays.  It 
wa^  also  observed  that  not  only  the  red  was  the  hottest  ray,  but 
th:it  there  was  a  point  a  little  beyond  the  red,  altogether  out  of 
th'3  spectrum,  where  the  thermometer  stood  higher  than  in  the 
red  it-elf.  The  mo,-t  inten  e  heat  was  always  beyond  the  red 
ray,  where  there  wai  no  Tght  at  all,  an  1  the  heat,  in  all  the  ex- 
periments, was  found  to  diminish  progressively,  from  the  red  to 
the  violet,  where  it  was  least.  These  invi  ible  rays  of  heat 
were  found  to  exert  a  very  considerable  effect  at  a  point  1^ 
inches  below  the  extreme  red  ray,  even  though  the  thermome- 
ter was  placed  at  a  distance  of  52  inches  from  tho  prism.  O  her 
experimenters  have  placed  the  point  of  maximum  heat  within 
the  red  rays  ;  and  the  point  is  found  to  vary  with  the  material  of 
which  the  prism  is  made.  With  a  prism  of  rock  salt,  Melloni 
succeeded  in  separating  the  point  of  maximum  temperature  to 
a  much  greater  distance  from  the  colored  parts  of  the  spectrum 
linn  had  previou  ly  been  done.  On  moving  the  therino-.Tierer 
below  this  point,  it  was  found  that  the  rays  of  heat  extended  a 
considerable  distance  below  the  colored  parts  of  the  spectrum. 
The  conclusion,  therefore,  is  irresistible,  that  there  are  in  the 
solar  beam  invisible  rays  of  heat,  of  different  refrangibillties,  and 
so  much  less  refrangible  than  the  light  that  the  central  ray  fills 
considerably  below  the  lower,  or  red  end  of  the  spectrum.  The 
shape  of  tho  thermal  spectrum  does  not  coincide  with  that  of 
light,  but  is  curiously  discontinuous,  consisting  of  several  dis- 
tinct parts,  and  forming  at  the  lower  end  three  round  spots,  B, 
c  and  D  ;  see  spectrum  of  heat,  Fig.  106. 

Where  is  tho  point  of  maximum  heat?  How  was  this  determined?  What  effect  has 
the  nature  of  the  prism  ou  the  point  of  maximum  heat?  What  is  the  shape  of  tao 
thermal  spectrum  ? 


258  THE    CHEMICAL    RAYS. 

279.  The  chemical  rays  of  the  solar  beam.  It  has  long 
been  known  that  the  light  of  the  sun  possesses  extraordinary 
chemical  power;  the  di-chloride  of  mercury,  or  calomel,  and 
the  chloride  of  silver,  commonly  called  lunar  caustic,  are  black- 
ened ;  transparent  phosphorus  becomes  opaque ;  and  the  color- 
ing principles  of  vegetable  origin  are  destroyed,  by  its  action. 
Solar  light  will  also  produce  the  instantaneous  combination  of 
the  two  gases,  chlorine  and  hydrogen.  On  the  other  hand,  it 
confers  upon  the  green  cells  of  the  leaves  of  plants  the  power 
of  decomposing  carbonic  acid ;  and  it  has  also  a  wonderful  influ- 
ence in  producing  the  green  cells  of  plants.  This  chemical 
energy  is  not  concentrated  at  any  one  point  in  the  spectrum,  but 
is  extended  through  several  of  the  colored  rays,  and  outside  of 
them  above  the  violet ;  whence  we  conclude  that  there  are  dif- 
ferent kinds  of  chemical  rays  in  the  solar  beam,  distinguished 
from  each  other  by  a  difference  in  refrangibility,  just  as  there 
are  different  kinds  of  heat,  and  different  kinds  of  light.  The 
point  of  maximum  chemical  effect  does  not  correspond  with  the 
maximum  point  for  light,  nor  with  the  maximum  point  for  heat, 
but  is  found  at  the  violet,  or  upper  end  of  the  spectrum,  Fiys. 
103  and  104.  Scheele  noticed  that  the  effect  of  the  violet  rays 
upon  the  chloride  of  silver  is  more  perceptible  than  that  of  the 
other  rays.  Dr.  Wollaston  ascertained  that  the  greatest  effect  is 
produced  just  outside  of  the  violet  rays.  The  spot  next  in  energy 
is  the  violet  itself,  and  the  effect  gradually  diminishes  in  advanc- 
ing to  the  green,  beyond  which  it  seems  to  be  wholly  wanting. 
Nitrate  of  silver  placed  in  the  red  rays  is  not  blackened  at  all. 
The  chemical  rays  are,  therefore,  more  refrangible  than  tho  e 
of  light,  in  consequence  of  which  they  are  dispersed  over  the 
blue,  indigo,  and  violet  spaces,  and  even  extend  a  considerable 
distance  outside  of,  and  above  this  end  of  the  spectrum ;  they 
are  often  called  actinic  rays.  It  is  also  said  that  other  rays 
have  been  discovered  in  the  spectrum  which  do  not  exercise 
any  chemical  action  of  themselves,  but  have  the  property  of 
continuing  it  when  once  commenced ;  they  are  thought  to  ex- 
tend from  the  indigo  beyond  the  violet,  and  are  called  pho.-phoro- 
genic  rays.  They  are  so  named  because  they  are  believed  to 
be  the  rays  which  are  absorbed  by  the  substances  called  phos- 
phorescent, already  described,  and  being  emitted  again  when 

279,  Give  some  illustrations  of  the  chemical  effect  of  the  sun's  rays,  Is  this  chemical 
energy  concentrated  at  one  point  in  the  spectrum  ?  Are  there  different  kinds  of  chemi- 
cal rays?  In  what  respect  do  they  duTcr?  Where  is  the  point  of  maximum  effect? 
What  are  phosphorogenic  rays  ?  What  is  the  shape  of  tue  chemical  spectrum  ? 


FLUORESCENCE. 
! 

these  bodies  are  carried  into  the  dark,  constitute  the  phenomena 
of  phosphorescence.  Some  experiments  of  Sir  John  Herschel 
seem  to  show  that  the  shape  of  the  chemical  spectrum  is  not 
the  same  as  that  for  light,  and  is  also  discontinuous,  like  that  of 
heat,  consisting  of  a  broad  band  between  the  orange  and  the 
yellow,  then  omitting  the  yellow,  commencing  again  at  the  green 
ray,  and  continuing  far  above  the  upper  end  of  the  violet, 
gradually  tapering  to  a  blunted  point.  See  Fig.  106. 

280.  The  range  of  the  chemical  rays  in  the  solar  spectrum. 
— FluDrercsnce.  The  invisible  rays  extend  beyond  the  violet 
extremity  of  the  spectrum  for  a  distance  nearly  equal  in  length 
to  twice  that  of  the  luminous  portion ;  but  in  the  electric  light 
obtained  by  the  ignition  of  charcoal  points,  the  invisible  spec- 
trum can  be  traced  nearly  six  times  as  far;  Figs.  104  and  106. 
On  transmitting,  however,  these  invisible  rays  through  certain 
substances,  such  as  a  solution  of  sulphate  of  quinine,  the  de- 
coction of  the  bark  of  the  horse  chestnut,  tincture  of  chlorophyll, 
&c.,  the  rays  become  visible  in  consequence  of  a  diminution  of 
their  refrangibility.  Thus,  if  a  tube,  filled  with  a  solution  of 
sulphate  of  quinine,  be  placed  in  the  invisible  rays,  entirely 
outside  of  the  spectrum,  and  above  the  violet  ray,  a  ghostlike 
gleam  of  blue  light  will  shoot  directly  through  the  tube,  and  on 
examining  the  blue  light  thus  obtained,  it  is  found  to  contain 
rays  of  much  less  refrangibility  than  the  violet,  and  not  much 
exceeding  tho>e  of  the  green  ray.  The  explanation  of  this 
singular  effect  is,  that  the  invisible  rays  have  had  their  refrangi- 
bility reduced  by  passing  through  the  quinine,  and  on  emerg- 
ence, possess  the  refrangibility,  color,  and  other  properties  of 
the  colored  rays  of  the  upper  part  of  the  spectrum ;  in  other 
words,  the  invisible  rays  have  been  absorbed  and  re-radiated 
in  a  condition  of  lower  refrangibility,  such  as  ordinarily  pro- 
duces the  impression  of  blue  light.  According  to  the  undula- 
tory  theory  of  light,  the  rate  of  undulation,  or  the  number 
of  vibrations  per  second  which  produces  the  invisible  rays, 
is  reduced  by  transmission  through  the  sulphate  of  quinine, 
aid  when  they  issue  again,  they  possess  only  the  number 
of  vibrations  which  produces  blue  light.  This  change  of  re- 
frangibility is  not  limited  to  the  invisible  rays  outside  the  lumi- 
nous spectrum,  but  can  be  accomplished  also  in  the  case  of  the 
visible  and  colored  rays.  In  every  case,  the  altered  rays  are 

230.  How  far  do  the  chemical  rays  extend  ahovo  the  violet  ?  What  is  the  effect  of  a 
solution  of  quinine  on  the  invisible  chemical  rays?  Explain  fluorescence,  SUto  what 
w  meant  by  the  degradation  of  H^ht? 

11* 


2GO 


TRIPLE    CHARACTER    OF    SOLAR    LIGHT. 


changed  into  those  which  are  less  refrangible,  and  the  change  is 
never  to  rays  of  greater  refrangibility.  This  singular  change 
of  refrangibility  has  received  the  name  of  the  degradation  of 
light,  and  is  analogous  to  the  change  of  refrangibility  produced 
in  rays  of  heat  when  they  are  absorbed  by  certain  substances, 
constituting  another  point  of  resemblance  between  these  two 
chemical  agents.  Bodies  which  have  the  power  of  effecting  it 
are  called  fluorescent,  from  fluor  spar. 

281.  The  triple  character  of  solar  light.  A  beam  of  s^ar 
light  is  therefore  composed  of  three  distinct  sorts  of  rays,  viz., 
the  heating,  the  illuminating,  and  the  chemical,  and  hence  is 
capable  of  producing  three  different  kinds  of  effects :  fii  st,  the 
effect  of  heat ;  second,  that  of  light ;  third,  that  of  chemical  in- 
fluence. In  a  beam  of  natural  sunlight,  the  different  rays  are,  as  it 
were,  intertwined,  like  the  triple  strands  of  a  cord,  and  their 
influence  is  exerted  at  one  and  the  same  spot ;  but  if  transmit- 
ted through  a  prism,  they  are  separated,  in  consequence  of  the 
difference  in  their  refrangibility,  and  their  maximum  influence 
is  manifested  at  three  distinct  points.  This  is  clearly  ehown  in 

Fig.  104,  in  which  the 
ray  of  sunlight,  a,  by 
the  refraction  of  the 
prism,  is  elongated  ?o  as 
to  extend  from  c  to  b. 
The  rays  of  heat  being 
less  refrangible  than 
those  of  light,  exhibit 
their  maximum  effect  at 
H,  below  the  red  rays, 
while,  however,  their 
general  influence  extends 
from  b  to  v,  or  to  the  up- 
per end  of  the  illumina- 
ting rays.  The  ch(  mical 
rays,  on  the  other  hand, 
being  more  refrangil  le 
than  those  of  light,  exhibit  their  maximum  effect  at  c,  a  point 
considerably  above  the  most  refrangible  of  the  illuminating 
rays,  while  their  general  influence  extends  from  c  to  R.  The 
illuminating  rays  extend  from  v  to  R,  and  the  maximum  effect 


Fig.  104. 


Unequal  refransibiliti/  of  the   Chemical,  Illumina- 
ting and  Heating  Rays  in  the  Solar  Beam. 


281.  Provo  the  triple  character  of  solar  light.     Why  are  the  foci  of  a  lens  for  light, 
.beat,  and  chemical  effect,  not  found  at  the  same  point  1 


DISSECTION    OF  2G1 

Fig.  105.  i3  exerted  at  Y,  while,  within  the  same 

limits,  a  certain  amount  of  heating  and 
chemical     influence     is     also     displayed. 
From  this,  it  is  evident,  that  the  solar 
beam  is  possessed  of  a  triple  nature,  and 
exerts,  wherever   it   falls,  three  distinct 
sorts   of  influence.     On   account   of   the 
different  refrangibility  of  these  three  sorts 
of  rays,  if  a  beam  of  solar  light  be  trans- 
mitted  through  a  lens,  they  will  not  all 
be  concentrated  at  the  same  focus,  the 
chemical  rays  being  the  most  refrangible,  will  have  their  focus 
at  a  point  c,  nearer  the  lens  than  the  focus  for  light,  L,  while 
the  rays  of  heat  will  be  collected  at  the  point  H,  more  remote 
from  the  lens  than  the  focus  for  light ;  Fig.  105.     It   follows 
from  this,  that,  if  the  greatest  chemical  effect  of  the  sun's  rays  be 
desired,  the  object  must  be  placed,  not  in  the  illuminating  focus, 
but  a  little  nearer  to  the  lens  ;  if  the  greatest  heating  effect  of 
the  sun's  rays  be  sought,  the  object  must  be  placed  a  little  far- 
ther from  the  lens  than  the  focus  for  light.     In  order  to  form 
a  correct  idea  of  the  solar  spectrum,  it  is  necessary,  also,  to 
bear  in  mind  that  the  different  spectra  are  not  all  continuous, 
nor  possessed  of  the  same  shape.     In  Fig.  106,  this  disconti- 
nuity, as  well  as  the  relative  extent  of  the  different  spectra,  and 
the  points  of  maximum  intensity,  are  well  represented,  together 
with  the  fixed  dark  lines  crossing  the  spectrum  at  right  angles, 
which  are  presently  to  be  described.     It  will  be  observed  that 
in  the  spectrum  for  light,  the  maximum  point  of  illumination  is 
in  the  yellow  ray,  and  that  the  fluorescent  rays  extend  a  con- 
siderable distance  above  the  upper  end  of  the  violet  ray.     In 
the  spectrum  for  heat,  the  shape  is  peculiar,  and  the  effect  at 
the  lower  part  limited  to  the  four  round  spaces,  A  B  c  D  while 
'the  point  of  maximum  intensity  is  considerably  below  the  yel- 
low, at  the  extreme  end  of  the  red  ray.     In  the  spectrum  of 
chemical  rays,  the  point  of  maximum  intensity  is  outside  the 
violet  ray,  and  the  continuity  of  the  spectrum  is  also  broken. 
In  the  case  of  Praunhofer's  lines,  it  will  be  noticed  that  they 
have  been  traced  a  considerable  distance  outside  of  the  illumi- 
nating rays  of  the  spectrum,  in  both  directions,  above  the  vio- 
let, and  below  the  red.     In  the  spectrum  formed  by  the  solar 
beam,  these  spectra  are  not  separated  from  each  other,  as  in  the 

What  is  their  position  in  reference  to  the  lens?    Describe  Fig.  106. 


2C2 


TIIZ  SUNBZAM:. 


Chem. 
Hays 


Fi°-  10G'  figure,  but  are  superim- 

posed ;  and  in  the  case 
of  any  unrefracted  solar 
beam  passing  through  a 
circular  aperture,  into  a 
darkened  room,  are  all 
intertwined,  and  concen- 
trated in  the  small  round 
spot  of  light  produced. 
282.  The  spectra 

f reduced  by  artificial 
ight  and  colored 
flames.  If  artificial 
light,  emanating  from 
different  luminous  bod- 
ies, be  transmitted 
through  a  prism,  it  is 
decomposed  in  the  same 
manner  as  the  solar 
beam,  and  a  spectrum  is 
formed,  consisting  of  the 
various  colors  which  pro- 
duce white  light,  but 
never  in  the  same  rela- 
tive intensity  and  pro- 
portions in  which  they 

The  Light.  Heat,  and  Chemical  Rays,  and  the  Dark      aPPear  hl  the  eolar  SPeC' 
Lines  of  the  Solar  Beam.  triim.       The  Color  which 

predominates  in  the 

artificial  light,  predominates  in  its  spectrum ;  a  red  flame  pro- 
duces a  spectrum  in  which  the  prevailing  hue  is  red ;  a  blue 
flame  a  spectrum  in  which  it  is  blue.  If  the  flame  be  a  pure 
red  or  blue,  the  spectrum  will  present  a  continuous  band  of  a  • 
red  or  blue  color.  There  is  no  artificial  light  which  is  not  defi- 
cient in  some  of  the  elements  of  solar  light.  Colored  artificial 
flames  may  be  produced  by  placing  the  salts  of  different  metals 
in  the  flame  of  an  alcohol  lamp,  or  gas  burner,  and  the  peculiar 
colors  imparted  have  long  been  used  by  chemists  as  indications 
of  the  presence  of  these  metals ;  thus  a  yellow  flame  is  caused 
by  the  salts  of  sodium ;  a  violet  flame  is  produced  by  those  of 
potassium ;  lithium  and  strontium  salts  give  a  red  flame,  and 


282.  Can  artificial  light  be  decomposed?    Does  the  spectrum  formed  differ  from  that 
of  the  sun  ?    Can  metals  be  detected  by  the  color  they  impart  to  flames  ? 


THE    SOLAR    SPECTRUM 


2G3 


.Fig.  107. 


the  salts  of  barium  tinge  the  flame  green.  The  value  of  these 
colored  flames,  as  a  means  of  detecting  the  metals,  is  diminished 
when  several  of  these  metals  are  present  at 
once,  because  the  color  produced  by  one  melal 
obscures  that  produced  by  another,  though  this 
difficulty  may  be  in  part  removed  by  the  use  of 
colored  glasses,  or  liquids,  through  which  the 
flame  is  observed.  If,  however,  these  colored 
flames  be  subjected  to  the  action  of  a  prism, 
and  the  spectrum  formed  be  examined  by  a 
powerful  telescope,  certain  characteristic  pecu- 
liarities may  be  observed  which  make  this  the 
most  delicate  means  of  qualitative  analysis  yet 
discovered. 

283.  The  solar  spectrum  not  continuous, 
but  crossed  by  fixed  dark  lines.— Fraunhofer  s 
lines*  The  solar  spectrum  not  only  contains 
heating  and  chemical,  as  well  as  illuminating 
rays,  but  also  exhibits,  when  carefully  exam- 
ined, a  great  number  of  dark  lines,  crossing  the 
spectrum  at  right  angles  to  the  order  of  the 
colors,  and  always  occupying  the  same  relative 
positions.  In  other  words,  the  solar  spectrum 
is  not  continuous,  but  is  separated  into  a  great 
number  of  portions,  of  unequal  size,  by  dark 
lines  of  division,  in  which  there  is  no  light. 
That  these  dark  lines  indicate  the  absence  of 
light,  is  shown  by  their  want  of  blackening 
effect,  and  their  correspondence  with  the  inactive 
spaces  which  are  observed  when  a  photograph 
is  taken  of  the  solar  spectrum.  These  lines 
were  first  noticed  by  Dr.  Wollaston,  in  1802, 
on  transmitting  solar  light  through  a  very  nar- 
row slit,  and  viewing  it  directly  by  the  eye 
placed  immediately  behind  the  prism.  In  1815, 
Fraunhofer,  a  distinguished  optician,  of  Munich, 
examined  the  solar  spectrum  thus  produced  by 
a  lens,  and  ascertained  the  existence  of  nearly 
600  dark  lines ;  of  these  he  published  an  accu- 
rate map,  selecting  seven,  on  account  of  their  distinctness,  and 
the  ease  with  which  they  may  be  recognized,  and  distinguishing 


283.  By  what  is  the  continuity  of  the  solar  spectrum  broken  ?    Describe  Fraunhofer'3 
lines.    Do  they  extend  beyond  the  limits  of  the  visible  spectrum  ? 


204 


CROSSED    BY    DARK    LINES. 


Fig.  108. 


them  by  the  letters  B,  c,  D,  E,  F,  G  and  H.  They  have,  since 
his  time,  been  ascertained  not  to  be  confined  to  the  colored  parts 
of  the  spectrum,  but  to  extend  beyond  the  violet  ray,  and 
through  the  whole  of  the  space  occupied  by  the  chemical  rays. 
These  lines  are  represented  in  Fig.  107,  and  are  known  by  the 
name  of  Fraunhofer's  lines.  B  is  in  the  red  space,  near  its 
ouler  end ;  c  which  is  broad  and  black,  is  beyond  the  middle 
of  the  red ;  D  is  in  the  orange  and  is  a  strong  double  line,  the 
two  lines  being  nearly  of  the  ssime 
size  and  separated  by  a  bright  one ; 
E  is  in  the  green,  and  consists  of  sev- 
eral lines,  the  middle  one  being  the 
strongest ;  F  is  in  the  blue,  and  is  a 
very  strong  line ;  G  is  in  the  indigo, 
and  H  in  the  violet.  Between  B  and 
c,  there  are  9  lines ;  between  c  and 
D,  there  are  30 ;  between  D  and  E, 
there  are  84 ;  between  E  and  F,  56  ; 
between  F  and  G,  185  ;  and  between 
G  and  H,  190.  In  order  to  observe 
them,  the  sun's  light  must  be  admit- 
ted through  a  narrow,  vertical  slit,  o, 
into  a  darkened  room,  and  allowed  to 
fall  upon  a  prism,  jo,  placed  with  its  axis 
parallel  to  the  slit,  Fig.  108,  and  at 
a  distance  of  about  24  feet  from  it. 
The  prism  is  fixed  before  the  object- 
glass  of  a  telescope,  /,  in  such  a  position 
that  the  angle  formed  by  the  incident 
ray  with  the  first  face  of  the  prism,  is 
equal  to  that  formed  by  the  refracted 
ray  with  the  second  face ;  eo  that  the 
position  of  tli£  prism  is  that  in  which 
the  light  is  subjected  to  the  minimum 
amount  of  di.-persion.  These  lines 
are  always  found,  whatever  be  the 

solid  or  liquid  medium  u?ed  in  the  construction  of  the  prism, 
and  whether  its  refracting  angle  be  great  or  email,  and  under 
all  circumstances  they  always  preserve  exactly  the  same  rela- 
tive position  in  the  respective  colored  spaces  in  which  they  occur. 
The  line  B,  for  instance,  is  always  found  at  the  same  relative 


Instrument  for  vif  icing  Fraun- 
hofer">s  Lines. 


How  can  these  lines  be  best  observed?    What  is  their  number?    How  can  they  be  Jis- 
£lyaed  upon  a  screen1?  •  --  ^  _. 


THE    SPECTRA    OF    ARTIFICIAL    LIGHT  265 

distance  from  the  extremity  of  the  red  space  in  the  spectrum, 
whatever  the  material  of  which  the  prism  is  made.  These 
lines  differ  very  much  in  appearance ;  some  are  extremely  fine, 
and  are  hardly  visible ;  others  are  very  near  each  other,  an  1 
resemble  a  cloud,  rather  than  distinct  lines;  and  there  are 
some  which  seem  to  possess  a  perceptible  breadth.  Fraua- 
hofer  counted  590  lines;  but  Sir  D.  Brewster  has  since  ex- 
tended the  number  to  2000.  These  lines  indicate  the  absence 
in  the  solar  beam  of  rays  of  certain  refrangibilities,  and  the 
reason  that  they  do  not  appear  in  the  spectrum  as  ordinarily 
formed,  is  the  superposition  of  spectra,  which,  in  the  more  per- 
fect spectrum  of  Fraunhofer,  does  not  exist.  The  greater  the 
elongation  of  the  spectrum,  and  the  more  widely  the  colored 
spaces  are  separated,  the  more  distinct  do  these  lines  become. 
If  it  be  desired  to  throw  the  spectrum  upon  a  screen,  it  may  be 

done  by  the  arrangement 

Fi"'  109<  shown  in  Fig.  10,).     It 

has  been  found  that  all 
light  proceeding  directly 
from  the  sun,  or  indirect- 
ly from  it  by  reflection, 
such  as  the  light  of  the 
moon  and  the  planets,  and 
the  light  reflected  from 

Fraunhofer^  Lines  displayed  vpon  a  Screen.  the    cl°uds   and  the    Pail1- 

bow,   gives    a   spectrum 

crossed  by  lines  exactly  identical.  It  is  a  point  of  great  interest 
to  determine  the  cause  of  these  dark  breaks  in  the  continuity 
of  the  solar  spectrum.  The  spectra  produced  by  the  light  of 
Sirius,  Castor,  and  other  fixed  stars,  are  also  all  crossed  by 
black  lines,  but  different  from  each  other,  and  from  the  sun, 
though  in  nearly  all,  some  of  the  most  important  black  lines 
found  in  the  solar  spectrum,  are  seen.  Thus,  in  Procyon,  the 
double  line,  D,  is  found ;  and  in  Capella  and  Beltegeux,  the 
lines  D  and  b.  Arcturus,  Aldebaran,  p  Pegasi,  and  <5  Virginia 
are  particularly  remarkable  for  the  strength  and  number  of  the 
lines  by  which  their  spectra  are  crossed. 

284.    Spectra  produced  by  the  light  of  the  Webulae,  and  by  > 
artificial  light,  are  crossed  by  bright,  instead  of  dark,  lines< 
While,  however,  the  spectra  of  the  sun  and  the  fixed  stars  are 
found  to  be  crossed  by  black  lines,  it  is  a  singular  fact  that  the 

What  kind  of  lines  arc  formed  in  the  spectra  of  the  moon,  and  the  planets  ?     Of  the 
fixed  stars  ?— 284-  What  kind  of  lines  in  the  spectra  of  the  Nebula  ?     Of  artificial  lights  ? 


266  CKOSSED    BY    BRIGHT    LINES. 

spectra  of  the  Nebulas,  in  the  heavens,  are  crossed  by  bright,  in- 
stead of  dark  lines ;  and  this  is  also  the  case  with  the  spectra 
produced  by  the  various  sources  of  artificial  light,  by  the  elec- 
tric light,  by  gas,  oil,  alcohol,  and  hydrogen.  The  spectrum  of 
the  electric  light  gives  a  very  bright  line  in  the  green  ray  ;  those 
of  hydrogen,  alcohol,  and  oil,  give  two  extremely  bright  lines  in 
the  red  and  orange.  The  spectra  furnished  by  colored  flames, 
produced  by  the  introduction  of  different  substances  into  the 
flame  of  an  alcohol  lamp,  give  lines  of  various  degrees  of  color 
and  brightness  scattered  through  the  whole  spectrum. 

285.  Spectrum  Analysis.  These  bright  lines  are  simply 
rays  of  light  of  different  degrees  of  refrangibility,  and  of  a  color 
peculiar  to  itself,  emitted  by  each  element,  when  intensely  heated. 
These  rays  are  mingled  with  the  rays  that  form  the  beam  of  light 
proceeding  from  the  flame  in  which  the  element  in  question  is 
ignited,  and  are  ordinarily  indistinguishable  ;  but  if  this  beam  be 
passed  through  a  narrow  slit  and  directed  upon  a  prism,  the  rays 
of  different  refrangibility  and  color  are  separated  fi  om  each  other, 
and  those  proceeding  from  the  ignited  element  make  their  appear- 
ance in  the  form  of  narrow  bright  spaces  or  lines  crossing  the 
spectrum  at  right  angles  to  its  length.  The  examination  of  the 
spectra  of  ignited  substances  constitutes,  therefore,  a  new  method 
of  chemical  analysis.  All  that  is  necessary  is  that  the  substance 
should  be  heated  to  the  degree  at  which  it  is  vaporized,  and  this 
vapor  made  luminous.  The  light  proceeding  from  an  ignited  solid 
body  unvaporized  like  the  light  of  perfectly  pure  carbon  points 
of  the  battery,  produces  only  a  continuous  spectrum,  not  crossed 
eiiher  by  bright  or  dark  spaces.  Many  of  the  metals  can  be  made 
to  give  their  characteristic  lines,  if  heated  in  the  flame  of  an  ordi- 
nary chemical  gas  burner ;  but  most  of  them  require  the  intense 
heat  of  the  electric  spark,  derived  either  from  the  galvanic  battery, 
or  from  Ruhmkorff  's  coil,  an  instrument  to  be  described  hereafter. 
'I  he  spark,  in  passing  between  two  points  of  the  metal  in  ques- 
tion, volatilizes  a  small  portion,  and  heats  it  so  intensely  as  to 
enable  it  to  give  off  its  peculiar  light.  The  permanent  gases 
also  yield  characteristic  spectra  if  a  discharge  from  a  powerful 
Kuhmkorff's  coil  be  passed  through  them.  Thus,  if  the  spark 
be  parsed  through  an  atmosphere  of  hydrogen,  the  light  emitted 
is  bright  red,  and  its  spectrum  consists  of  one  bright  red,  one 
green,  and  one  blue  line,  while  in  nitrogen,  the  light  is  purple, 

2?5.  What  effect  is  produced  upon  the  lines  in  the  spectra  of  artificial  light  by  ignited 
nn-tals  1  Is  the  power  of  producing  characteristic  lines  in  the  spectrum  confined  to  the 
metals?  Can  the  gases  be  m*de  to  give  characteristic  lines?  How  can  we  trace  the 
lined  beyond  the  limits  of  the  visible  spectrum? 


SPECTKOI    ANALYSIS.  267* 


and  the  position  of  the  lines  entirely  different.  When  a 
pound  gas,  or  vapor,  is  ignited  by  the  electric  spark,  the  spectra 
produced  are  those  of  the  elementary  components  of  the  gas. 
At  these  intense  temperatures,  chemical  combination  seems  to 
be  impossible,  and  the  various  elements  are  able  to  coexist  in  a 
separate  form,  mechanically  intermingled.  If  photographs  of 
these  spectra  be  taken,  the  impression  obtained  contains  all  the 
lines  characteristic  of  the  elements  in  question.  The  photo- 
graph being  produced  by  the  chemical  and  extra  violet  rays, 
gives  a  spectrum  which  extends  much  beyond  the  limits  of  the 
violet  ray,  and  contains  lines  not  seen  when  the  spectrum  is 
viewed  through  the  telescope;  see  Fig.  107.  The  minutest 
quantities  of  the  different  elements,  if  ignited,  will  give  the 
characteristic  lines  with  perfect  distinctness,  and  if  several  ele- 
ments happen  to  be  contained  in  the  same  flame,  the  lines 
peculiar  to  each  are  as  plainly  seen  as  they  would  have  been 
had  no  others  been  present.  Sodium  gives  a  single  or  double 
line  of  yellow  light  in  a  position  corresponding  to  that  of  the 
orange  rays  in  the  solar  spectrum.  Potassium  gives  a  red  line 
in  the  red  end  of  the  spectrum,  and  a  violet  line  tit  the  violet 
end.  Lithium  gives  a  dark  spectrum,  with  only  two  bright 
lines,  one  a  pale  yellow,  corresponding  to  the  yellow  portion  of 
the  spectrum  ;  the  other  a  bright  red,  in  the  red  end  of  the 
spectrum.  Strontium  presents  eight  characteristic  bright  lines. 
Calcium  gives  one  broad  green  band,  and  one  bright  orange 
band,  besides  several  smaller  orange  lines.  Messrs.  KirchhofF 
and  Bunsen,  to  whom  we  are  indebted  for  the  first  investigation 
of  this  subject,  state  that  the  amount  of  sodium  which  can  'be 
detected  in  this  manner  need  not  exceed  the  190,000,000th 
part  of  a  grain  ;  of  lithium,  the  70,000,000th  part  ;  of  po'as- 
sium,  the  60,000th  part  of  a  grain  ;  bromine  the  same  ;  stron- 
tium, the  1,000,000th;  calcium,  the  100,000,000th  part  of  a 
grain.  The  yellow  line  of  sodium,  No.  3,  Fig.  Ill,  is  always 
found,  whatever  be  the  kind  of  light  employed.  This  is  owing 
to  the  extensive  diffusion  of  this  element  in  the  atmosphere, 
and  its  presence  in  every  substance  which  has  been  exposed  to 
the  a'rr  for  however  short  a  time.  Lithium,  which  was  form- 
erly supposed  to  be  contained  in  only  four  minerals,  by  the  aid 
of  spectrum  analysis,  has  been  observed  in  almost  all  spring 
waters,  in  tea,  tobacco,  milk,  and  blood,  but  existing  in  such 

St:it<>  the  characteristic  lines  of  sodium.     Potassium.     Lithium.     Strontium.     Calci- 
um.    How  minute  a  quantity  of  each  cau  thus  be  detected? 


268 


THE    SPECTROSCOPE. 


minute  quantities  as  to  have  eluded  detection  by  the  less  deli- 
cate methods  of  analysis. 

206.   The  Spectroscope.    The  instrument  used  in  these  re- 
searches is  called  the  Spectroscope,  Fig.  110.     It  consists  of  a 

Fig.  110. 


The    Spectroscope. 

prism,  p,  mounted  vertically  upon  a  firm  iron  stand,  F,  and  a 
tube,  A,  carrying  a  lens  at  the  end  nearest  the  prism,  and  at  the 
other  extremity  having  a  very  fine  vertical  slit  lor  the  admission 
of  the  light.  The  width  of  this  slit  can  be  regulated  by  the 
small  screw,  e.  The  stand,  s,  carries  a  sliding  rod,  which  sup- 
ports the  substance  to  be  analyzed,  in  the  flame  of  the  gas 
burner,  E.  This  burner  is  placed  oppo-ite  one  half  of  the  slit, 
and  its  light  passes  directly  down  the  tube  to  the  prism ;  oppo- 
site the  other  half  of  the  slit  is  placed  a  small  rectangular  pri.-  m, 
the  object  of  which  is  to  reflect  the  light  proceeding  from 
some  other  source,  as  the  sun,  or  any  artificial  light,  D,  al^o 
down  the  axis  of  the  tube.  By  this  arrangement,  spectra,  pro- 
ceeding from  two  different  sources,  are  formed,  one  above  the 
other,  and  can  readily  be  compared,  so  as  to  decide  whether 

286.  Describe  the  Spectroscope.— 287.  What  new  metals  have  been  discovered  ? 


THE    SPECTRUM    OF    THE    SUN  269 

their  lines  coincide,  or  differ.  The  light  having  been  refracted 
by  the  prism,  is  received  by  the  telescope,  B,  and  the  image  of 
the  spectrum  magnified  before  reaching  the  eye.  The  telescope 
is  movable  in  a  horizontal  plane,  upon  the  tripud,  and  can  be 
adjusted  so  as  to  observe  every  part  of  the  spectrum  formed  by 
the  prism.  The  tube,  c,  contains  a  lens  at  the  extremity  near- 
est the  prism,  and  at  the  other,  a  scale  formed  by  transparent 
lines  on  an  opaque  ground ;  this  tube  is  adjusted  in  such  a  way 
that  a  light  being  placed  at  the  open  extremity,  the  image  of 
the  scale  is  reflected  by  the  prism  into  the  telescope,  B,  for  the 
purpose  of  reading  off  the  position  of  the  bright  and  dark  lines 
of  tha  spectrum,  as  both  will  appear  simultaneously  placed  side 
by  side  in  the  field  of  the  telescope.  When  the  instrument 
is  used,  stray  light  is  excluded  by  covering  it  with  a  loose  black 
clolh.  The  dispersion  of  the  spectrum  may  be  much  increased 
by  using  several  prisms  instead  of  one.  The  prism  is  some- 
times made  hollow,  and  filled  with  bi-sulphide  of  carbon. 

237.  The  new  metals  discovered  by  spectrum  analysis. 
In  the  course  of  his  researches  upon  the  bright  lines  in  the 
spectra  produced  by  the  alkalies,  the  German  chemist,  Bunsen, 
observed  several  lines  which  could  not  have  been  produced  by 
the:n,  and  which  led  him  to  suspect  the  existence  of  a  new 
m  'tal.  On  evaporating  40  tons  of  the  mineral  waters  of  Durck- 
hbim  and  Baden,  he  obtained  105  grains  of  the  chloride  of  a 
new  metal,  which,  on  being  introduced  into  the  spectroscope, 
gave  two  splendid  'violet  lines,  and  is  called  Caesium,  from 
c(zs>'us, — bluish  gray.  In  the  waters  of  Hallein  and  Gastein, 
there  was  discovered  another  new  metal,  Rubidium,  from  rubi~ 
dus,  dark  red,  because  it  has  two  splendid  red  lines  in  its  spec- 
trum. A  third  metal,  called  Thallium,  has  since  been  discov- 
ered, so  called  from  OuW)^,  a  budding  tivig^  in  allusion  -to  the 
brilliant  green  line  presented  by  its  spectrum.  Indium  was 
recognized  by  the  presence  of  a  hitherto  unobserved  fine  dark 
blue  line.  The  peculiar  appearance  of  the  spectra  of  several 
of  the  metals,  as  seen  through  the  spectroscope,  is  represented 
in  Fig.  Ill,  the  dark  lines  of  the  solar  spectrum  being  repre- 
sented in  black,  the  differently  colored  lines  of  the  other  spec- 
tra in  white.  No.  1  represents  the  solar  spectrum ;  No.  2,  that 
of  potassium ;  No.  3,  that  of  sodium,  its  bright  line  being  iden- 
tical in  position  with  the  dark  solar  line,  D ;  No,  4,  that  of  the 
new  metal,  rubidium  ;  No.  o,  that  of  another  new  metal,  caesium.* 
The  spectra  of  the  same  me.als  are  represented  in  colors  iu 
the  Frontispiece, 


270  COMPARED    WITH    THOSE    OF    THE    METALS. 


Fig.  111. 

1.  2.  3.  4.  5. 

Solar  Spectrum.     Potassium.  Sodium.  Rubidium.  Caesium. 


The  dark  lines  in  the   Solar  Spectrum,  compared  with  the  bright  lines  in  the  Spectra 
of  Potassium,  Sodium,  Rubidium  and  Ccesium, 


THE    DARK    LINES    OF    THE 


271 


Fig.  ill  * 


288.  The  dark  lines  of 
the  solar  spectrum  exactly 
coincident  with  the  bright 
lines  of  spectra  produced  by 
the  metals.  Kirthhoff',  in  ex- 
perimenting on  the  bright 
lines  found  in  the  spectra 
produced  by  the  burning 
metals,  discovered  that  these 
bright  lines  are  in  many  cases 
exactly  coincident  with  the 
dark  lines  mapped  by  Fraun- 
hof'er,  in  the  solar  spectium, 
so  that  when  the  two  lights 
are  thrown  into  the  tube 
through  the  same  slit,  and 
their  spectra  are  seen  through 
the  same  telescope,  B,  %'iy. 
110,  arranged  one  above  the 
other,  the  bright  lines  of  the 
one  are  found  to  be  continued, 
without  the  slightest  inter- 
ruption, into  the  daik  lines 
of  the  other.  Thus  sodium, 
for  example,  when  ignited, 
emits  an  intensely  biilliant 
yellow  light,  which  is  concen- 
trated into  two  closely  con- 
tiguous bands,  or  bright  lines, 
coincident  in  position  with 
Fraunhofer's  double  black 
line,  D,  in  the  solar  spectrum ; 
it  was  also  found  that  the 
bright  lines  characteristic  of 
potassium,  chromium,  mag- 
nesium, iron,  and  nickel,  ex- 
actly correspond  with  certain 
of  the  black  solar  spectra 
lines;  vaporized  iron  gave 
about  60  bright  lines,  coincid- 
ing in  position,  and  in  breadth, 
with  the  same  number  of 
black  lines  produced,  by  the 
sun. 

In  Fig,  11 1*,  a  representa- 
tion is  given  of  the  coinci- 


272  SOLAR 

dence  of  more  than  60  of  the  bright  lines  in  the  spectrum  of 
Iron,  with  as  many  dark  lines  in  the  spectrum  of  the  sun.  It 
seems  impossible  that  this  should  be  an  accidental  coincidence, 
and  it  at  once  sugge?>ted  the  idea  that  they  are  dne  to  the  same 
cause,  and  that  the  dark  lines  in  the  solar  spectrum  are  pro- 
duced by  these  metals,  ignited  in  the  atmosphere  of  the  sun. 
The  only  difference  is,  that  in  the  one  case  the  lines  are  bright, 
in  the  other  they  are  dark.  The  probability  that  such  a  coinci- 
dence should  be  a  mere  chance,  instead  of  really  indicating  the 
presence  of  Iron  in  the  sun's  atmosphere  is,  according  to  the 
doctrine  of  probabilities,  only  1  to  1,152,930,000,000,000.000. 
289.  The  bright  lines  afforded  by  metallic  spectra  convert- 
ed into  dark  lines.— The  dark  lines  of  the  solar  spectrum  ex- 
plained. Now  it  has  been  found  that  the  bright  lines  of  the 
metallic  spectra  may  be  converted  into  black  lines,  by  placing 
behind  the  flame  in  which  the  metal  is  ignited  another  flame, 
much  more  intense  than  the  first,  and  containing  the  same  metal 
in  a  state  of  more  intense  ignition.  For  instance,  if  through 
the  flame  of  a  common  alcohol  lamp,  colored  by  sodium,  the 
more  powerful  light  of  sodium,  heated  by  hydrogen,  or  by  the 
electric  light,  be  transmitted,  the  bright  lines  found  in  the  spec- 
trum of  the  first  sodium  light,  are  instantly  changed  into  black 
lines,  occupying  the  same  position ;  the  bright  lines  in  the  spectra 
of  potassium,  lithium,  barium,  and  strontium,  may  be  converted 
into  black  lines,  in  a  similar  manner.  In  other  words,  if  any 
element  be  ignited  and  vaporized  at  a  high  temperature,  it  emits 
rays  of  light  of  a  definite  degree  of  refrangibility,  and  of  a 
color  peculiar  to  itself  These  rays  are  mingled  with  the  rays 
that  form  the  beam  of  light  proceeding  from  the  flame  in  which 
the  element  is  ignited,  and  ordinarily  are  indistinguishable  ;  but 
if  this  beam  be  passed  through  a  narrow  slit,  and  directed  upon 
a  prism,  the  rays  of  different  refrangibility  and  color  are  sepa- 
rated from  each  other,  and  those  proceeding  from  the  ignited 
element  make  their  appearance  in  the  form  of  narrow  bright 
spaces  or  lines  crossing  the  spectrum  at  right  angles  to  its  length. 
If,  however,  immediately  behind  the  flame  in  which  the  element 
is  ignited,  another  flame  be  placed  much  more  intense  than  the 
first,  and  containing  the  same  element  in  a  state  of  more  intense 
ignition,  so  that  the  rays  of  light  which  it  emits  will  be'trans- 
mitted  through  the  rays  emitted  by  the  element  contained  in 
the  first  flame,  the  rays  of  the  same  refrangibility  in  both  flames 
will  virtually  destroy  each  other,  just  as  the  waves  of  different 
sounds  sometimes  do,  producing  perfect  silence,  so  that  when 


SPKCTKUM    EXPLAINED.  273 

the  different  rays  are  separated  from  each  othor  by  the  prism, 
certain  rays  will  be  found  to  be  wanting,  and  dark  spaces  to 
have  taken  their  places  in  which  there  is  no  light.  If  no\v,  in 
the  atmosphere  of  the  sun  the  vapors  of  the  various  meta's  be 
present  in  a  state  of  intense  ignition,  their  light  passed  through 
a  prism  and  decomposed  would  produce  a  prism  filled  with 
bright  lines,  but  if  behind  this  external  luminous  atmosphere 
of  th^  sun  there  be  another  source  of  heat  still  more  intense, 
and  containing  these  same  metals  in  a  state  of  mo;e  intense 
ignition,  and  converted  into  luminous  vapor,  the  first  bright 
lines  will  be  converted  into  dark  lines  by  the  absorption  of  the 
rays  of  light  which  produce  them,  and  by  the  consequent  for- 
mation of  dark  spaces  in  the  solar  spectrum  in  which  there  is 
no  lijjrht.  Now  this  is  precisely  the  view  which  astronomers 
are  disposed  to  give  of  the  constitution  of  the  sun.  Within 
an  external  luminous  Photosphere  there  is  supposed  to  be  an 
internal  solid  or  liquid  nucleus,  in  a  more  intense  state  of  igni- 
tion. It  is  therefore  highly  probable  that  the  unilluminated  or 
dark  spaces  in  the  solar  spectrum  are  produced  by  this  cause, 
and  that  the  vapors  of  the  following  metals — Iron,  Sodium,  Po- 
tassium, Calcium,  Magnesium,  Manganese,  Chromium,  Nickel, 
Titanium,  Hjdrogenium,  Barium,  Cobalt,  and  Aluminium, — 
are  contained  in  the  sun's  Photosphere,  and  most  likely,  also, 
Zinc,  Copper,  and  Gold,  and  that  these  metals  also  exist  to  a 
considerable  extent  in  UK;  internal  Nucleus  of  the  sun.  And 
that  on  the  other  hand,  as  the  bright  lines  of  the  spectra  of 
Silver,  Mercury.  Antimony,  Arsenic,  Tin,  Lead,  Cadmium, 
Strontium,  and  Lithium,  also  Silicon  and  Oxygen,  do  not  coin- 
cide with  any  of  the  dark  lines  of  the  solar  spectrum,  therefore 
these  elements  do  not  exist  at  all  in  the  constitution  of  the  sun. 

289.*  The  Solar  Spectrum  is  sometimes  crossed  by  bright 
instead  of  dark  lines.  If  the  light  of  the  external  Photosphere 
of  the  Sun  could  be  observed  by  itself,  alone,  and  separated 
from  that  of  the  internal  nucleus,  according  to  this  theory,  a 
solar  spectrum  would  be  obtained,  crossed  by  the  same  system 
o\  Fraunhofer  lines  as  now,  only  reversed,  and  made  bright 
instead  of  dark. 

This  state  of  things  takes  place  during  the  occurrence  of  a 
total  solar  eclipse,  for  then  the  moon  coming  between  the  earth 
and  the  sun,  completely  cuts  off  all  light  proceeding  from  the 
bo'dy  of  the  sun,  and  no  light  can  reach  the  earth  except  that 
which  proceeds  from  the  solar  Photosphere,  and  tlie  incandes- 
cent vapors  which  surround  it.  AVhen  the  sun's  disk  is  viewed 


276  BRIGHT   LINES. 

the  strength  and  number  of  the  dark  lines  by  which  their  spec- 
tra are  crossed.  From  this  we  infer  that  the  constitution  of 
the  Fixed  Stars  is  similar  to  that  of  the  Sun,  that  is,  that  they 
till  have  an  internal  luminous  nucleus,  surrounded  by  an  exter- 
nal luminous  Photosphere  less  intensely  heated.  We  are  also 
able  to  ascertain  with  considerable  accuracy  the  chemical  con- 
stitution of  these  heavenly  bodies.  Thus  Aldebaran  contains 
Hydrogen,  Sodium,  Magnesium,  Calcium,  Iron,  Tellurium,  An- 
timony, Bismuth,  and  Mercury,  while  in  Sirius,  only  Sodium, 
Magnesium,  and  Hydrogen,  have  been  detected. 

292.*  Spectra  of  the  Nebulae.  The  spectra  of  the  Nebula, 
differ  from  those  of  the  Sun  and  of  the  Stars,  as  they  contain 
only  bright  lines,  rnnng  which  the  Nitrogen  and  Hydrogen 
lines  are  very  apparent.  Hence  we  conclude  that  the  .Nebulas 
are  only  masses  of  glowing  gas,  and  do  not  consist,  like  the 
Sun,  of  an  incandescent  solid  or  liquid  nucleus,  surrounded 
by  a  gaseous  Photosphere. 

293.*  Spectra  of  Comets  and  Meteors.  Observations  upon 
the  spectra  of  Comets  seem  to  show  that  the  nuclei  consist  of 
glowing  gas,  most  probably  containing  Carbon,  and  that  they 
not  only  emit  their  own  light,  but  also  reflect  a  portion  of  that 
of  the  Sun.  On  the  other  hand,  the  spectra  of  Meteors  show 
that  they  are  incandescent  solid  bodies,  and  that  they  differ 
from  each  other  in  chemical  constitution,  some  containing 
Sodium,  others  Magnesium. 

291*.  Spectra  of  the  Aurora  Borealis  and  of  Lightning-.  T1  e 
spectra  of  the  Aurora  also  exhibit  very  distinct  and  beautiful 
bright  lines,  but  none  that  are  coincident  with  those  of  any  of 
the  terrestrial  elements.  Hence  we  conclude  that  these  are 
absent,  or  that  the  heat  is  not  sufficiently  great  to  make  them 
luminous.  The  spectra  of  Lightning  are  also  crossed  by  bright 
lines,  some  of  which  are  coincident  with  those  of  Nitrogen  and 
Oxygen,  and  are  probably  produced  by  the  electrical  ignition 
of  the  gaseous  mixture  of  Oxygen,  Nitrogen,  Watery  Vapor, 
and  Carbonic  Acid,  through  which  the  discharge  is  made. 

Thns  we  have  the  means,  by  carefully  observing  the  light 
emitted  by  the  various  heavenly  bodies,  of -determining  not  only 
their  physical  constitution,  but  also  the  chemical  elements 
which  enter  into  them.  This  is  the  most  brilliant  generaliza- 

Describe  the  method  of  observing  them.  What  is  the  principal  substance  discovered  in 
the  solar  prominences  ?  290*.  Describe  the  spectra  of  the  moon  and  of  the  planets 
291*.  Describe  the  spectra  of  the  fixed  stars.  What  elements  are  found  in  them? 
292*.  Describe  the  spectra  of  the  Nebulae.  293*.  Describe  the  spectra  of  Comets  aud 
of  Meteors.  294*.  Describe  the  spectra  of  the  Aurora  Borealis,  and  of  Lightning. 


THE    EFFECT    OF    SOLAR    LIGHT  277 

tion  of  modern  chemistry,  and  in  this  way  does  the  chemist 
possess  the  power  of  extending  his  researches  beyond  the  earth, 
and  determining  the  chemical  constitution  of  the  sun  and 
stars,  and  that  too  with  a  degree  of  exactness  far  surpassing 
that  of  the  ordinary  means  of  analysis. 

290.  The  clfcct  of  Solar  Light  on  the  Vegetable  Kingdom. 
The  combined  influence  of  the  three  kinds  of  rays  contained  in 
the  sunbeam  upon  all  objects  exposed  to  their  action  is  un- 
doubtedly very  great.  This  is  seen  especially  in  the  case  of 
plants.  Without  the  influence  of  the  heating  rays  of  the  sun- 
beam, plants  evince  no  signs  of  life,  and  in  general,  the  higher 
the  temperature,  the  more  abundant  and  luxuriant  the  vegeta- 
tion. The  effect  of  the  illuminating  rays  is  equally  marked. 
In  the  dark,  it  is  well  known  that  the  growth  of  plants  is 
checked,  and  that  their  tissues  are  soon  almost  entirely  deprived 
of  their  green  color,  and  turn  white  ;  their  juices,  also,  lose  their 
peculiar  characteristic  properties  and  become  tasteless  and 
Avatery.  All  plants  tend  to  grow  towards  the  light,  and  if 
placed  in  cellars,  are  soon  bent  in  the  direction  of  the  windows. 
There  is  also  a  certain  mechanical  effect  exerted  by  the 
solar  beam ;  under  its  influence  the  stomata  of  the  leaves  are 
opened,  and  the  amount  of  air  and  watery  vapor  exhaled  and 
inhaled  is  greatly  increased  ;  if  this  influence  be  withdrawn,  the 
stonata  are  at  once  closed,  and  the  respiration  of  the  plant  is 
entirely  suspended.  Plants,  therefore,  placed  in  absolute  dark- 
ness, speedily  die.  There  is  another  effect,  however,  exerted 
by  the  chemical  rays  of  the  solar  beam,  of  at  least  equal  im- 
portance. The  green  parts  of  leaves  and  stems  acquire  the 
power,  under  the  influence  of  sunlight,  of  decomposing  carbonic 
acid,  appropriating  the  carbon,  and  exhaling  nearly  pure  oxygen. 
In  the  dark,  this  process  is  rever.-ed,  and  carbonic  acid  is  ex- 
haled ;  but  as  the  amount  of  oxygen  produced  is  much  larger 
than  the  amount  of  carbonic  acid,  the  general  effect  of  plants 
is  to  diminish  the  amount  of  carbonic  acid  in  the  atmosphere, 
and  to  increase  the  amount  of  oxygen.  They  tend,  therefore, 
to  fit  the  air  for  the  support  of  animal  life,  and  to  neutralize  the 
injurious  influences  exerted  upon  the  atmosphere  by  the  car- 
bonic acid  produced  by  the  breathing  of  animals.  There  are 
two  periols  in  the  growth  of  plants  when  the  amount  of  car- 

29:).  What  is  the  effect  of  the  heat  rays  of  the  solar  beam  on  plants  ?  Of  the  illuminating 
rays ?  What  is  the  effect  of  light  on  the  stomata  of  leaves?  What  happens  if  plants  be 
pliced  in  complete  darkness?  What  effect  has  light  on  the  decomposition  of  carbonic 
aci'l  by  plants?  Is  this  process  ever  reversed?  At  what  two  periods  in  the  life  of  the 
plants  is  carbonic  acid  produced  in  excess?  Vkat  effect  has  light  on  oxidation?  On 
de -oxidation? 


278  ON    VEGETATION, 

bonic  acid  evolved  is  greatly  increased,  viz.,  the  germination  of  the 
seeds,  and  the  bursting  of  the  flower-buds;  especially  the  former. 
This  is  owing  to  the  fact,  that  in  both  these  processes  a  large 
amount  of  carbon  is  removed  from  the  starch  contained  in  the 
seed  and  flower,  in  order  that  it  may  be  converted  into  sugnr. 
Oxygen  is,  therefore,  absorbed  from  the  atmosphere  to  unite  with 
this  carbon  and  convert  it  into  carbonic  acid,  which  is  then  ex- 
haled. Both  these  processes  are  greatly  assisted  by  the  absence 
of  light,  and  one  of  the  indispensable  conditions  of  vegetation 
is,  that  the  seed  be  buried  in  the  ground,  and  kept  in  the  dark. 
The  absence  of  light  tends,  therefore,  to  accelerate  combination 
with  oxygen,  or  to  produce  oxidation;  the  presence  of  light  to 
set  free  oxygen  from  substances  containing  it,  or  to  produce 
de-oxidation.  It  is  by  this  latter  process  that  all  the  carbon 
contained  in  plants  has  been  abstracted  from  the  atmosphere, 
by  the  agency  of  leaves,  and  also  all  the  coal  now  found  buried  in 
the  bowels  of  the  earth.  These  influences  are  exerted  chiefly 
by  the  chemical  rays  of  the  sunbeam,  and  they  are  greatly  in- 
creased by  covering  plants  with  blue  glass.  This  has  the  effect 
of  absorbing  the  rays  of  heat  and  light,  and  leaving  the  plant 
to  the  exclusive  influence  of  the  chemical  rays. 

291.  Summary  of  the  effects  of  Light  on  Vegetation. 
The  general  effect  of  sunlight  on  plants  may  be  thus  summed  up  : 
1st.  The  illuminating  rays  prevent  the  germination  of  seeds- 
2d.  The  chemical  rays,  formed  at  the  violet  extremity  of  the 
spectrum,  and  extending  a  considerable  distance  beyond  it, 
quicken  germination.  3d.  The  luminous  rays  effect  the  decom- 
position of  carbonic  acid  by  the  leaves.  4th.  The  chemical 
and  luminous  rays  are  both  essential  to  the  formation  of  the 
coloring  matter  of  leaves.  5th.  The  chemical  and  illuminating 
rays,  unassisted  by  the  calorific  rays,  prevent  the  development 
of  the  reproductive  organs  of  plants.  6th.  The  heat  rays,  cor- 
responding with  the  extreme  red  rays,  assist  the  development 
of  the  reproductive  organs  of  plants.  There  seems  to  be  a  nice 
adaptation  of  sunlight  to  the  varying  condition  of  vegetation, 
at  the  different  seasons.  In  the  spring,  when  the  process  of 
germination  is  going  on,  there  is  a  large  excess  of  chemical 
rays,  which,  as  we  have  seen,  tend  powerfully  to  hasten  the 
process.  The  excess  of  the  chemical  rays,  at  this  season  of  the 

How  has  all  the  coal  been  abstracted  from  the  atmosphere?  By  what  rays  of  the  solar 
beam  has  this  been  done?  What  effect  has  blue  glass  upon  plants?— 291.  Give  a  sum- 
mary of  the  effect.-!  of  lig'it  on  vegetation.  How  does  sunlight  seem  to  be  adapted  to  the 
var>  in<r  condition  of  vegetation  ? 


AND  ON  CHEMICAL  COMPOUNDS.  279 

f 

year,  is  proved  by  the  greater  facility  with  which  photographic 
operations  may  be  carried  on.  As  summer  advances,  and  the 
influence  of  the  illuminating  rays  is  required  to  promote  the 
decomposition  of  carbonic  acid  by  the  leaves  and  the  conse- 
quent growth  of  vegetation,  the  quantity  of  the  illuminating 
and  heating  rays  both  increase  in  a  very  great  degree  relatively 
to  the  chemical  rays.  In  the  autumn,  as  plan-s  approach  matu- 
rity, and  seeds  are  to  be  formed,  and  fruit  ripened,  the  illumi- 
nating and  chemical  rays  both  diminish,  and  the  heating  rays 
are  increased.  This  furnishes  a  very  extraordinary  and  curi- 
ous instance  of  design  in  Nature.  Advantage  is  often  taken  of 
these  principles  by  the  horticulturist,  in  the  cultivation  of  plant*. 
When  the  seeds  are  to  be  forced,  they  are  covered  with  dark 
blue  glass,  because  this  absorbs  all  the  illuminating  and  calorific 
rays,  and  allows  only  the  chemical  rays  to  reach  the  plant.  As 
the  plant  advances  towards  maturity,  light  is  needed,  and  yellow 
glass  is  substituted  in  place  of  blue.  When  the  period  of 
maturity  arrives,  heat  has  become  more  es  ential,  and  red  glass 
is  employed  in  place  of  the  yellow.  In  this  manner  the  gar- 
dener closely  imitates  the  changes  in  the  composition  of  sun- 
light which  are  made  in  Nature. 

292.  The  effect  of  Solar  Lijjht  on  Chemical  Compounds. 
Several  instances  have  already  been  adverted  to,  of  the  chemi- 
cal effect  of  the  sun's  rays  ;  chlorine  and  hydrogen  will  unite 
with  explosion,  and  the  chloride  of  silver  will  be  blackened  if 
placed  in  the  bright  siml'ght.  In  all  these  cases  the  effect  is 
produced  by  the  chemical  rays  of  the  sunbeam,  and  not  by 
those  of  heat  or  light,  for  if  the  beam  be  decomposed  by  a 
prism,  and  the  different  rays  separated  from  each  other,  those 
of  heat  and  light  may  be  entirely  excluded,  and  yet  the  effect 
remain  the  same.  An  important  application  is  made  of  this 
influence  of  the  chemical  rays  in  the  art  of  Photography,  or 
the  formation  of  pictures  by  the  agency  of  the  sun.  These 
pictures  are  generally  produced  by  the  action  of  the  chemical 
rays  of  the  sunbeam  on  some  salt  of  silver.  The  explanation 
of  the  chemical  part  of  the  process  must  be  deferred  for  the 
present,  and  the  mechanical  details  only  given  here.  The 
outline  of  any  object  can  be  taken  by  the  following  simple  pro- 
cess. Let  a  piece  of  white  paper  be  moistened  with  a  diluted 
solution  of  common  salt,  and  then  washed  over  with  a  solution 

How  does  the  gardoner  imitate  Nature  in  this  respect?— 292.  What  is  the  effect  of 
sunlight  on  chemical  combination  ?  On  chloride  of  silver  ?  By  what  rays  in  the  sunbeam 
is  this  effect  produced  ?  How  is  this  proved  ?  What  art  depends  upon  this  effect  of  light  ? 

12 


280  THE    DAGUERREOTYPE. 

of  nitrate  of  silver.  Common  salt  consists  of  chlorine  and 
sodium,  and  by  the  action  of  the  chlorine  the  nitrate  of  silver 
is  converted  into  the  chloride  of  silver,  a  substance  which 
speedily  turns  black  on  exposure  to  the  sunlight.  This  black 
color  is  due  to  a  chemical  change  in  the  chloride,  in  virtue  of 
which,  either  an  oxide,  or  some  peculiar  form  of  chloride  of 
silver,  of  a  black  color,  is  produced.  If,  on  paper  thus  prepared, 
before  it  has  been  exposed  to  the  light,  any  &mall  object  be 
placed,  which  is  perfectly  opaque,  and  then  the  whole  exposed 
to  the  action  of  the  sun,  the  paper  will  I  e  blackened,  except  where 
it  has  been  protected  by  the  article  in  question  ;  thus  a  white 
spot  will  be  produced  upon  a  dark  ground,  having  the  exact 
o  itline  of  the  article  employed,  and  this  white  gj.ot  may  be 
prevented  from  turning  black  on  exposure  to  the  light,  and  pre- 
served permanently  white,  by  washing  the  paper  immediately 
in  a  saturated  solution  of  common  salt,  by  which  all  the  chlo- 
ride of  silver  is  dissolved  our,  and  the  paper  left  in  its  natuial 
condition.  If  the  article  in  question  be  not  entirely  opaque, 
but  partially  translucent,  the  paper  under  it  will  have  leen 
more  or  less  blackened,  corresponding  wiih  the  amount  of  light 
transmitted,  and  in  this  way  various  degrees  of  shade  produc  ed 
which  may  be  rendered  permanent  in  the  manner  above  de- 
scribed. It  was  on  this  principle  that  Wedgewood  arid  Davy, 
about  1802,  undertook  to  prepare  photographic  pictures,  by  pio- 
jecting  the  shallow  of  the  article  intended  to  be  copied,  upon 
wrliite  paper  and  leather,  saturated  with  a  eolution  of  nitrate  of 
silver;  but  unfortunately  their  attempts  failed  in  consequence 
of  inability  to  fix  the  pictures,  and  render  them  indestiuctible 
by  diffused  light. 

293.  The  Daguerreotype  process.  The  next  improvement 
in  taking  photographic  pictures  consisted  in  the  us-e  of  the 
camera  obscura.  By  this  instrument  a  luminous  image  can  "be 
formed  in  the  interior  of  a  darkened  box ;  and  if  this  image  be 
allowed  to  fall  upon  a  polished  silver  plate,  or  upon  properly 
prepared  paper,  a  picture  will  be  formed  which  only  nt  eds  pro- 
tection from  the  action  of  diffused  light,  after  being  taken  firm 
the  camera,  in  order  to  be  permanent.  M  Daguerre,  who  was 
the  inventor  of  the  process  which  bears  his  name,  made  use  of 
p'ates  of  silver  coated  with  iodine,  by  exposure  to  the  fumes 
which  rise  from  this  substance  on  the  applicat:on  of  heat ;  in 
this  way  a  thin  film  of  iodide  of  silver  is  formed  upon  the 

How  may  the  outline  of  an  object  be  taken?    AVho  first  undertook  to  prepare  photo- 
grap.iic  outlines  by  tills  process? — 293.  Describe  tae  Dujjuerreot.,  pe  process. 


THE    PHOTOGRAPH.  281 

surface.  It  is  then  exposed  for  a  few  moments  to  the  action 
of  light  in  the  camera,  the  effect  of  which  is  to  decompo.  e 
the  iodide  of  silver,  and  expose  the  pure  metal  to  a  greater  or 
less  degree,  according  to  the  light  and  shade  of  the  image  within 
the  instrument.  The  plate  is  then  removed  from  the  camera, 
and  as  quickly  as  possible  transferred  to  a  darkened  room,  whore 
it  is  held  over  the  fumes  of  heated  mercury ;  these  mercurial 
fumes  act  upon  the  silver  wherever  it  has  been  laid  bare  by  the 
action  of  the  light,  and  to  a  degree  proportioned  to  this  action, 
and  thus  a  difference  of  surface  and  color  are  produced  between 
the  image  and  the  other  parts  of  the  plate,  and  it  now  only  re- 
mains to  remove  the  undecomposed  iodide  of  silver  from  the 
o'.her  portions  of  the  plate,  and  render  it  incapable  of  being 
affected  by  the  action  of  the  diffused  light  of  day,  in  order  to 
make  the  picture  complete.  This  is  effected  by  washing  the 
plate  with  a  solution  of  the  hypo-sulphite  of  soda,  which  dis- 
solves off  all  the  remaining  sensitive  coating.  It  is  then  cov- 
ered with  a  very  thin  film  of  reduced  gokl,  for  the  purpose  of 
giving  to  the  picture  a  richer  and  wanner  tone.  This  i;  accom- 
plished by  pouring  upon  the  plate  a  solution  of  chloride  of  gold, 
and  heating  it  over  the  flame  of  a  spirit  lamp. 

291.  Photographs.  About  the  same  time  that  the  process 
for  taking  pictures  upon  iodized  silver  plates  was  introduced  by 
M.  Daguerre,  Mr.  Talbot  invented  a  similar  process  for  taking 
pictures  upon  paper  prepared  with  a  solution  of  iodide  of  silver. 
The  paper  is  placed  in  the  camera  in  the  manner  just  described, 
and  the  invisible  picture  which  is  formed  is  developed  by  wash- 
ing it  with  a  solution  of  gallic  acid,  the  superfluous  iodide  of  sil- 
ver being  quickly  removed  by  washing  with  a  solution  of  hypo- 
sulphite of  soda.  The  picture  thus  formed  is  then  placed  upon 
a  second  sheet  of  iodized  paper,  and  both  are  exposed  to  the 
direct  rays  of  the  sun.  In  consequence  of  the  partial  trans- 
parence of  the  paper,  the  rays  of  light  are  enabled  to  pass 
through  the  first  sheet  more  or  less,  according  to  the  degree  of 
light  and  shade  of  the  picture,  and  falling  upon  the  lower  sheet, 
speedily  develop  a  second  picture  upon  its  sensitive  surface. 
As  the  darkest  portions  of  the  first  picture  were  produced  by 
tin  most  highly  illuminated  parts  of  the  object,  the  picture  of 
which  was  taken,  it  is  quite  evident  that  in  the  second,  the  light- 
est portions  will  be  produced  beneath  the  darkest  portions  of 
the  first,  in  consequence  of  the  obstruction  which  these  offer  to 

294.  Describe  the  simplest  photographic  process. 


282  PHOTOGRAPHS 

the  passage  of  light,  and  that  the  darkest  portions  of  the  peeond 
picture  will  correspond  with  the  lightest  portions  of  the  first,  and 
consequently  the  lights  and  shades  of  the  second  picture  \vi  I 
exactly  correspond  with  the  lights  and  shades  of  the  orig'iinl 
object.  This  process  not  only  possesses  the  advantage  of  cheap- 
ness and  portability,  but  also  the  additional  one  of  allowing  the 
multiplication  of  impressions  indefinitely,  without  again  havh  g 
recourse  to  the  camera,  and  of  giving  an  exact  reproduction  of 
the  original  object ;  but  it  is  defective  in  delicacy  in  conse quern  e 
of  the  coarseness  of  the  fibre  of  paper,  even  when  manufactuicd 
with  the  greatest  care  and  expressly  for  photographic  purposes. 
The  next  improvement  consisted  in  the  substitution  of  glass 
plates,  coated  with  iodide  of  silver  through  the  instrumentality 
of  a  delicate  and  transparent  paste,  made  of  the  whites  of  eggs. 
The  transparent  medium  now  most  commonly  employed,  is  col- 
lodion ;  this  is  a  solution  of  gun  cotton  in  ether.  The  plate  of 
glass  is  first  rubbed  very  dry  and  clean,  with  linen  and  leather ; 
it  is  then  placed  in  a  horizontal  position,  and  upon  the  middle 
portion  a  quantity  of  liquid  collodion,  having  some  iodide  of 
potassium  dissolved  in  it,  is  poured,  and  the  superfluous  liquid 
allowed  to  drain  off.  The  collodion  soon  evaporates,  and  the 
plate  acquires  a  cloudy  appearance.  It  is  then  immediately 
plunged  into  a  bath  containing  4  grains  of  nitrate  of  silver,  to 
every  10  grains  of  water ;  the  iodine  at  once  quits  the  potassium 
and  unites  with  the  silver,  to  form  an  iodide  of  silver,  which  is 
deposited  in  a  thin  film  over  the  wrhole  plate ;  the  process  is 
carried  on  in  a  dark  room,  in  order  that  it  may  not  be  affected 
by  the  diffused  light.  After  remaining  about  a  minute  in  the 
bath,  the  plate  is  drained,  dried,  and  placed  in  a  closed  frame, 
fitting  tightly  into  the  groove3  of  the  camera.  When  it  is  ad- 
justed in  its  proper  place,  the  slide  which  protects  it  is  remove  d, 
and  the  iodized  plate  of  glass  exposed  to  the  action  of  the  lumi- 
nous image  formed  in  the  interior  of  the  camera.  The  iodide 
of  silver  is  everywhere  decomposed  to  a  degree  proportioned 
to  the  light,  the  brightest  parts  of  the  image  producing  the  deep- 
est impression,  but  without  exhibiting  any  apparent  picture. 
It  is  then  removed  from  the  camera  into  a  darkened  room,  and 
washed  with  a  solution  of  pyro-gallic  acid,  containing  a  slight 
amount  of  crystallized  acetic  acid.  Wherever  the  iodide  of  sil- 
ver has  experienced  the  beginning  of  decomposition,  there  is 

Describe  the  collodion  process.  How  is  the  superfluodjfiodide  of  silver  romove-1  ? 
What  is  a  negative  ?  A  positive  ?  Hoy  are  the  lights  aud  fcadw  of  tae  negative  picture 
reversed  in  the  positive? 


ARE    PRODUCED    BY    THE 


283 


formed  the  black  gallate  of  silver,  and  the  image  immediately 
appears.  The  shaded  parts  of  the  object  whose  picture  is  made, 
having  produced  no  effect  upon  the  iodized  glass  plate  within 
the  camera,  at  these  points  no  darkening  effect  is  produced  when 
it  is  dipped  into  the  gallic  acid,  and  the  undecomposed  iodide 
remains  entirely  unchanged.  As  this  would  speedily  become 
blackened  under  the  influence  of  diffused  daylight,  it  is  quickly 
washed  off  by  a  solution  of  hypo-sulphite  of  .soda.  Thus  there 
is  formed  upon  the  glass  plate  a  representation  of  the  original 
object,  in  which  the  lights  and  shades  are  reversed,  the  bright 
parts  being  dark  upon  the  plate,  and  the  dark  parts  cf  the  ob- 
ject being  perfectly  colorless  and  transparent;  consequently, 
the  picture  thus  obtained  is  called  a  negative.  In  order  to  pro- 
duce a  positive  picture,  or  an  exact  reproduction  of  the  original 
object,  the  negative  plate  i&  laid  upon  a  piece  of  paper  pre- 
pared with  chloride  of  silver,  and  the  two  sheets  being  com- 
pressed between  two  plates  of  glass,  the  whole  is  exposed  to 
the  action  of  bright  sunlight.  The  dark  parts  of  the  plate 
become  the  light  parts  of  the  new  picture,  and  the  light  parts  of 
the  plate  the  dark  parts,  thus  forming  a  perfect  reproduc  ion 
of  the  lights  and  shades  of  the  original  object.  The  paper  is 
then  washed  in  a  solution  of  hypo-sulphite  of  soda,  in  order  to 
remove  the  superfluous  chloride  of  silver,  and  the  picture  is 
complete.  It  is  evident  that  from  a  single  negative  on  glass, 
of  this  description,  an  indefinite  number  of  positive  pictures 

may    be    obtained 

F»s-  112-  by  a  proce-s  which 

may  be  considered 
a  kind  of  printing 
by  the  sun.  This 
constitutes  the  art 
of  photography,  in 
its  most  perfect 
form. 

295.  The  Pho- 
tographic Came- 
ra. In  Fig.  H  2  is 
represented  the  ar- 
rangement of  the 
camera  obscura, 
for  the  taking  of  Ja- 

Tht  Photographic   Camera.  gUCrreotypCS      and 


295.  Describe  the  photographic  camera- 


284  CHEMICAL  RAYS  ALONE. 

photographs.  The  lens  is  placed  at  A,  and  turned  towards  the 
person  or  object  the  image  of  which  is  to  be  taken.  Its  focus 
can  be  altered  by  means  of  the  screw  D.  The  glass,  or  the  sil- 
ver plate,  is  fastened  upon  a  frame,  which  is  slid  into  a  groove, 
E  B,  made  capable  of  adjustment  in  reference  to  the  lens  by 
moving  it  in  or  out  of  the  body  of  the  instrument,  c.  It  will 
be  observed  that  the  image  of  the  object  is  inverted.  The  images 
produced  by  single  lenses  are  always  inverted,  but  this  evidently 
presents  no  practical  difficulty.  In  the  actual  use  of  the  instru- 
ment, an  additional  slide  is  employed,  not  seen  in  the  figure,  by 
which  the  light  of  the  room  is  entirely  cut  off  from  the  plate, 
and  the  process  carried  on  in  total  darkness.  For  full  particu- 
lars in  reference  to  this  beautiful  art,  reference  must  be  made  to 
special  treatises  on  Photography. 

296-  Photographs  are  produced  solely  by  the  chemical 
rays  of  the  solar  beam.  The  process  of  forming  daguerreotype 
and  photographic  pictures  depends  solely  upon  the  chemical 
rays  of  the  solar  beam,  i.  e.,  upon  the  rays  that  are  found  in  the 
solar  spectrum,  above  the  violet,  and  entirely  outside  of  llie 
luminous  limits  of  the  spectrum,  extending  in  Fig.  104,  from  v 
to  c.  The  name  photography,  which  means  "  Light  drawing,"  is 
therefore  misapplied  to  this  art,  because  the  light  of  the  so'ar 
beam,  instead  of  producing  the  pictures,  actual'y  tends  to  pre- 
vent their  formation.  That  this  is  true,  may  1  e  proved  by  tak- 
ing a  daguerreotype  in  the  dark,  by  the  use  of  the  obscure,  OE- 
chemical  rays,  alone.  Let  a  large  solar  spectrum  be  thrown 
upon  a  screen,  and  at  the  point  c,  between  v  and  c,  Fig.  104, 
beyond  the  luminous  rays,  where  the  chemical  rays  are  situated, 
let  a  lens  be  placed  in  such  a  way  as  to  throw  these  rays  into  a 
darkened  apartment,  upon  the  object  who?e  picture  is  to  be 
produced ;  from  the  object  they  may  be  received  upon  sensitive 
pholographic  paper  arranged  in  the  camera  and  a  picture  taken 
in  the  ordinary  manner.  That  it  is  the  actinic,  or  chemical  lays, 
which  produce  the  picture,  is  also  proved  by  the  following  experi- 
ments. Throw  the  prismatic  spectrum  upon  a  table,  and  place  in 
it  slips  of  photographic  paper,  prepared  with  chloride  of  silver ; 
then  bring  out  the  effect  by  means  of  some  developing  agent. 
It  will  be  found  that  the  darkening  is  the  deepest  in  the  indigo 
and  violet  spaces,  and  that  it  extends  upwards  to  a  considerable 
distance  beyond  the  visible  spectrum.  If  traced  in  the  opposite 
direction,  it  is  found  to  diminish  rapidly  in  intensity,  until  it 

W*,.  By  what  ravs  in  the  solar  beam  are  photographs  produced  1    How  may  this  be 
proved  by  photographic  paper  1    By  flowers  and  pieces  of  glass  of  diSereut  colors  *, 


ALL  SURFACES  ARE  AFFECTED 


285 


Fig.   113. 


Yiolet. 

Indigo, 

Blue 

Green. 

Yellow . 
Orange. 

Red. 


Visible     Chemical 
Spectrum.  Spectrum. 


reaches  the  green  colored  space,  and  then  to  cease  entirely. 
fj.  113  illustrates  this,  and  shows  very  plainly  that  in  the  red, 
orange,  yellow,  and  green,  there  is  no  dark- 
ening effect  whatever  produced.  Again, 
take  a  vase  of  flowers,  of  different  shades, 
— scarlet,  blue,  and  yellow, — and  make  a 
photographic  copy  of  them  upon  iodide  of 
silver.  The  blue  tints  will  be  found  to  act 
most  violently  upon  the  sensitive  paper, 
while  the  red  and  yellow  are  scarcely  vi  i- 
ble.  Again,  take  a  sheet  of  sensitive  paper, 
prepared  with  chloride  of  silver,  and  place 
upon  it  strips  of  blue,  yellow,  and  red  g'ass. 
On  exposure  to  the  sun's  rays  for  a  few  min- 
utes, the  part  beneath  the  blue  glass  darkens 
rapidly,  while  those  covered  by  the  red  and 
yellow  glass,  are  perfectly  protected.  This 
is  the  more  striking  from  the  extreme  trans- 
parency of  the  plate  of  yellow  glass,  and  the  ease  with  which 
the  light  strikes  through  it,  and  the  nearly  complete  opacity  of 
the  plate  of  blue  glass,  hardly  allowing  of  the  passage  of  light 
at  all. 

297.  Practical  importance  of  distinguishing-  between  the 
illuminating-  and  chemical  rays  of  Light.  As  the  Photograph!  t 
requires  the  use  of  the  chemical  rays  of  the  solar  beam,  it  is 
necessary  for  him  to  pay  constant  attention  to  the  peculiar  prop- 
erties of  these  rays,  and  the  various  circumstances  which  affect 
them.  As  they  are  more  refrangible  than  the  illuminating  rays, 
they  are  brought  to  a  focus  at  a  point  somewhat  nearer  the  lens 
than  the  rays  of  heat  and  light,  Fig.  105,  and  in  the  arrange- 
ment of  the  camera,  the  plate  must  be  adjusted  accordingly. 
In  the  copying  of  natural  objects,  it  will  be  found  that  the  less 
refrangible  colors,  from  green  to  red,  inclusive,  send  for.h  no 
chemical  rays,  and  therefore  make  no  impression  upon  the  sen- 
sitive surfaces  which  are  employed,  and  produce  no  picture. 
Figures,  therefore,  of  green,  yellow,  and  red,  have  of  late  years 
been  very  generally  introduced  for  the  purpose  of  preventing 
tha  counterfeiting  of  government  and  other  notes.  In  the  tak- 
ing of  photographs,  it  is  not  always  the  brightest  day  that  is 

297.  Why  must  attention  he  paid  to  fie  chemical  rays  of  sunlight  in  adjusting  the 
camera?  What  is  the  advantage  of  introducing  colored  figures  into  bank  notes?  Why 
la  the  brightest  day  not  necessarily  favorable  to  photography  ?  Why  are  the  windows  of 
photographic  artists  glazed  with  blue  glass? 


28G 


i;r  THE  SUN  s  LIGHT. 


the  most  favorable,  on  account  of  the  predominance,  on  such 
days,  of  the  yellow  rays ;  and  for  the  same  reason,  the  autumn, 
— when  such  hues  predominate  in  the  landscape, — is  not  favor- 
able for  pictures  of  natural  objects.  The  sensitive  plates  are 
a  faithful  index  of  the  light  of  the  atmosphere.  The  artist  will 
frequently  have  occasion  to  notice,  on  prolonging  his  labors 
until  the  evening,  that  a  sudden  diminution  of  the  sensibility  of 
the  plates  begins  to  take  place,  at  a  time  when,  perhaps,  but 
little  difference  can  be  detected  in  the  brilliancy  of  the  light ; 
the  setting  sun  has  sunk  behind  a  cloud,  and  all  chemical  action 
is  soon  at  an  end.  If  the  light  is  at  all  of  a  yellow  cast,  how- 
ever bright  it  may  be,  its  chemical  powers  will  be  very  small. 
For  this  reason,  in  order  to  cut  off  the  yellow  and  red  rays 
which  may  be  reflected  from  common  objects,  upon  those  which 
are  to  be  photographed,  it  is  usual  to  g^aze  the  windows  of  the 
apartment  with  blue,  or  violet  colored  glass.  This  imparts  a 
blue  tinge  to  all  the  objects  in  the  room,  and  at  the  same  time 
effectually  absorbs  the  yellow  and  red  rays  that  may  exist  in 
the  atmosphere ;  thus  the  object  to  be  photographed  emits  a 
larger  proportion  of  chemical  rays,  and  its  outline  becomes 
much  more  distinct. 

298.  All  surfaces  are  affected  "by  the  sun's  light.  It  has 
been  seen  that  certain  substances  are  peculiarly  susceptible  to 
impressions  from  the  chemical  rays  of  the  solar  beam ;  but  it 
has  been  ascertained  that  the  sun's  rays  can  hardly  fall  upon  a 
surface  of  any  kind  without  producing  a  molecular  change,  and 
leaving  a  permanent  impression.  If  an  engraving,  which  has 
for  some  time  been  kept  in  the  dark,  be  exposed  to  the  sunlight 
upon  one-half  of  its  surface,  while  the  other  is  covered,  and 
then  be  removed  to  a  dark  room,  and  a  piece  of  prepared  pho- 
tographic paper  laid  upon  it,  the  part  of  the  engraving  which 
was  exposed  to  the  light  is  taken  upon  the  sensitive  paper, 
while  the  covered  part  produces  no  effect.  An  engraving  which 
has  been  subjected  to  the  action  of  the  sun's  rays,  and  then 
placed  in  the  dark,  will  reproduce  an  image  of  itself  upon  pho- 
tographic paper,  at  the  distance  of  quarter  of  an  inch,  without 
contact.  Indeed,  one  object  can  hardly  touch,  or  approach 
another,  without  producing  some  impression  upon  its  surface. 
The  effects  exerted  upon  bodies  by  the  action  of  sunlight  are 

293.  Do  the  chemical  rays  of  the  snnbenm  produce  .in  impression  upon  any  except 
specially  prepared  surfaces?  How  is  this  illustrated  in  the  case  of  an  engraving  exposed 
to  the  light  and  carried  into  a  darkened  room  ?  What  effect  is  produced  upon  these  in- 
fluences of  light  during  tLe  night?  Is  a  period  of  darkness  essential  to  the  normal  con- 
dition of  matter? 


RELATIONS    OF    THE    RAYS.  287 

obliterated  during  the  night,  and  a  period  of  darkness  seems  to 
be  essential  to  restore  the  normal  condition  of  all  the  various 
forms  of  matter. 

299.  The  relations  of  the  rays  of  Heat,  Xiight,  and  chemi- 
cal effect  in  the  Solar  Spectrum.  It  is  thought  that  the  undula- 
tions which  give  rise  to  the  sensation  of  heat,  are  slower 
than  those  of  light  and  chemical  influence,  but  that  all  are  pro- 
duced by  the  exceedingly  rapid  vibrations  of  the  molecules  of 
bodies,  communicated  to  the  particles  of  an  all-pervading  eiher, 
and  carried  along  by  it  with  wonderful  celerity.  The  slowest 
and  longest  of  these  vibrations  cause  undulations  of  a  low  de- 
gree of  refrangibility,  which  produce  the  sensation  and  other 
effects  of  heat ;  as  they  increase  in  speed,  the  degree  of  refran- 
gibility is  increased,  and  the  intensity  of  the  heat  a'so  aug- 
mented; as  the  vibrations  become  more  frequent,  the  refrangibility 
is  still  further  increased,  and  the  effect  of  dull  red  light  produced. 
By  a  still  further  increase  in  speed,  the  heating  effect  is  dimin- 
ished, refrangibility  is  still  more  increased,  and  the  effect  of 
bright  red  light  produced.  By  a  still  further  increase  in  speed, 
t'.ie  effect  of  heat  altogether  ceases,  the  red  brightens,  and  passes 
into  the  orange,  and  from  orange  to  yellow,  where  the  maximum 
effect  of  light  is  attained.  The  speed  of  the  undulations  rising 
still  higher,  the  effect  of  light  is  diminished,  the  yellow  passes 
into  the  green  and  blue,  refrangibility  is  still  further  increased, 
and  chemical  effect  first  begins  to  show  itself.  This  increases 
rapidly,  as  the  blue  parses  into  violet,  and  attains  its  maximum 
a  little  beyond  that  end  of  the  spectrum  ;  after  which,  this  effect 
also  diminishes,  and  the  vibrations  probably  cease  altogether. 
The  conversion  of  heat,  light,  and  chemical  power,  into  each 
other,  is  thus  seen  to  be  simply  a  change  in  the  rate  of  undu- 
lation. The  conversion  of  these  forces  into  ordinary  motion, 
and  their  production  from  it,  are  also  seen  to  be  readily  expli- 
cable as  a  mere  change  of  the  mode  of  motion,  affording  another 
illustration  of  the  convertibility  of  Forces. 

I 

Experiments :     Light. 

1.  The  ignition  of  solids  is  a  source  of  light ;  this  may  be  shown  by  settirg  fire  to  a 
j<>t  of  hydrogen  gas,  arid  introducing  into  the  flame,  which  is  almost  invisible,  a  piece  of 
platinum  wire ;  the  light  is  at  once  greatly  increased.  Introduce  fine  iron,  steel  and 
copper  wire ;  a  piece  of  glass  tube ;  the  finely  sharpened  end  of  a  piece  of  porcelain, 

299.  How  do  the  ethereal  vibrations  which  produce  heat,  compare  in  rapidity  with 

those  which  produce  light  and  chemical  influence?     Trace  the  gradual  passage  of  the 

rays  of  he;it  into  those  of  light  and  chemical  effect.     May  these  forces  be  regarded  as 

only  different  rates  in  the  motion  of  the  molecules  of  matter?  . 

12* 


288  EXPERIMENTS. 

chalk  and  marble ;  shake  some  calcined  magnesia,  and  powdered  charcoal,  through  the 
flaino ;  in  every  case  there  is  a  great  increase  in  the  brilliancy  of  the  light.  The  In  drogen 
may  be  prepared  by  pouring  sulphuric  acid,  diluted  with  five  times  its  volume  of  water, 
and  allowed  to  cool,  upon  granulated  zinc  in  a  glass  flask,  fitted  with  a  cork,  through 
which  passes  a  glass  tube,  drawn  out  to  a  fine  nozzle.  The  gas  must  be  allowed  to  escape 
from  the  nozzle  for  at  least  five  minutes  before  lighting,  in  order  to  completely  expel  the 
atmospheric  air,  otherwise  there  will  be  an  explosion. 

2.  Galvanic  electricity  is  a  source  of  light ;  this  may  be  shown  by  binding  a  piece  of 
•well  burned  charcoal,  or  prepared  carbon,  to  each  of  the  wires  attached  to  the  poles  of  a 
battery  of  12  Grove's  cups,  bringing  the  points  near  enough  for  the  current  to  pass, 
and  then  drawing  the  charcoal  points  slowly  apart  to  a  short  distance ;  the  light  is  very 
vivid. 

3.  Crystallization  is  a  source  of  light ;  this  is  best  seen  by  dissolving  transparent  arsen- 
ious  acid,  or  common  arsenic,  in  boilii.g  chlorohydric  acid,  until  a  saturated  solution  is 
made,  and  then  allowing  it  to  cool  in  a  darkened  room  ;  a  flash  of  light  may  be  seen  to 
accompany  the  deposition  of  each  crystal 

4.  Chemical  action  is  a  source  of  light ;  this  will  become  apparent  from  many  of  the 
experiments  which  are  to  follow,  especially  the  burning  of  phosphorus  in  oxygen. 

5.  The  law  of  the  reflection  of  light  may  be  shown  in  the  same  way  as  that  of  the  re- 
flection of  heat.     See  experiment  30,  page  78. 

6.  The  reflection  of  light  may  also  be  shown  by  the  large  parabolic  mirrors  ;  see  §  75.  p. 
61.     If  one  of  these  mirrors  be  placed  opposite  to  the  sun,  a  spot  of  extremely  intense 
light  and  heat  will  be  formed  in  its  focus ;  many  of  the  metals  will  be  made  red-hot,  and 
combustible  substances  inflamed. 

7.  The  refraction  of  light ;  this  may  be  shown  by  a  large  double  convex  lens  ;  also  by 
a  solid  prism  of  flint  glass;  or  still  more  effectively  by  a  hollow  prism  of  glass  filled  with 
bi-sulphide  of  carbon. 

8.  The  solar  spectrum  may  be  displayed  to  the  best  advantage  by  allowing  a  beam  of 
sunlight  to  enter  a  darkened  room  through  an  exceedingly  fine  slit,  in  the  manner  de- 
scri»>ed  in  §  276.  and  receiving  the  spectrum  upon  a  screen  of  white  cotton  cloth,  placed 
at  a  distance  of  20  feet  from  the  prism. 

9.  The  different  heating  power  of  the  rays  may  be  shown  by  placing  a  very  delicate 
thermometer  successively  in  the  colored  spaces,  from  the  violet  to  the  red,  and  finally  a 
little  below,  and  outside  of  the  red  ray. 

10.  The  different  illuminating  power  of  the  rays  may  be  shown  by  holding  a  printed 
page  successively  in  the  different  colors. 

11.  The  different  chemical  power  of  the  rays  may  be  shown  by  placing  slips  of  un- 
glazed  white  paper,  that  have  been  dipped  in  a  colorless  solution  of  nitrate  of  silver,  and 
immediately  afterwards  in  a  solution  of  common  salt,  in  the  dark,  successively,  one  slip 
in  each  color,  from  the  red  to  the  violet,  and  beyond  the  violet,  for  about  one  minute 
each ;  or  by  exposing  a  piece  of  prepared  paper  to  the  action  of  the  Avhole  spectrum. 
See  §§  278  and  279. 

12.  The  power  of  sunlight  to  produce  chemical  combination,  may  be  shown  by  mix- 
ing equal  volumes  of  chlorine  and  hydrogen  in  a  small  glass  tube,  supported  over  mer- 
cury, in  the  dark,  or  diffuse  dayl'ght,  and  reflecting  a  beam  of  sunlight  upon  it  by  a 
mirror  ;  only  a  small  quantity  of  the  gases  should  be  employed.     If  a  large  quantity  be 
used,  the  mixture  should  be  placed  in  a  bottle  of  white  glass,  in  a  wooden  'nox,  with  a 
movable  cover,  which  may  be  drawn  off  by  a  string  from  a  convenient  distance.     The  ex- 
plosion is  violent.     The  mode  of  preparing  these  gases  may  be  seen  by  referring  to  the 
experiments  under  each. 

1 3.  The  power  of  decomposing  carbonic  acid,  imparted  to  green  leaves  by  sunlight,  may 
be  shown  by  placing  a  thriving  plant  in  a  jar  of  carbonic  acid  gas,  and  exposing  it  to  the 
sunlight  for  some  days.     Test  the  presence  of  the  carbonic  acid  at  the  beginning  of  the 
experiment,  by  inserting  a  lighted  taper;  it  will  be  extinguished.     Prove  the  conversion 
of  tie  carbonic  acid  into  oxygen  at  the  close  of  the  experiment,  by  introducing  the  same 
taper,  re-lighted  ;  it  will  r.ow  burn  with  increased  brilliancy. 

14-.  That  the  leaves  of  plants  emit  oxygen  in  the  sunlight,  may  be  shown  by  placing 
a  sprig  of  mint  in  a  white  glass  globe,  filled  full  of  spring  water,  and  then  inverted  in  a 
tumbler  of  water,  and  placed  in  the  sun ;  in  a  short  time  babbles  of  gas  will  collect, 
which  may  be  proved  to  be  pure  oxygen  by  their  effect  on  a  lighted  taper. 

1?.  The  effect  of  sunlight  on  cherried  compounds,  may  be  shown  by  pouring  a  little 
solution  of  common  salt  into  a  wine  glass  containing  a  solution  of  nitrate  of  silver,  and 
exposing  the  white  precipitate  to  the  action  of  the  sun ;  it  is  almost  immediately  black- 
ened. 

1 6.  The  different  chemical  effect  of  light  of  different  colors,  mar  be  shown  by  exposing 
slips  of  papor,  prepared  by  dipping  in  a  solution  of  nitrate  of  silver,  and  then  in  one  cf 
common  salt,  in  the  dark,  under  pieces  of  blue,  yellow  and  red  glass,  to  the  action  of 
sunlight.  The  effect  will  be  decidedly  the  greatest  under  the  blue,  and  least  under  the 
red  glass. 


ELECTRICITY.  289 

17.  Fraunhofer's  lines  may  readily  be  seen  by  means  of  an  instrument,  arranged  as  in 
§  283,  or  by  the  Spectroscope,  §  28ti,  substituting  sunlight,  in  place  of  artificial  light. 

18.  The  existence  of  chemical  substances  in  tlames,  may  be  shown  by  employing  the 
Spectroscope,  as  described  in  §§  285  and  286,  or  by  receiving  the  spectrum  on  a  screen, 
as  in  §  284. 

19.  The  conversion  of  the  bright  lines  of  the  spectra  of  artificial  light  into  dark  lines, 
may  be  shown  by  forming  a  spectrum  upon  a  screen,  by  means  of  the  Spectroscope,  and 
the  light  of  a  powerful  lamp,  and  noting  the  bright  double  sodium  line  in  the  orange ; 
this  is  due  to  the  universal  diffusion  of  sodium  :  then  ignite  a  piece  of  sodium  in  a  small 
platinum  spoon,  in  a  gas  burner,  placed  so  as  to  intercept  the  light  of  the  original  lamp 
in  its  passage  into  the  Spectroscope,  and  the  bright  sodium  lines  of  the  spectrum  will  be 
at  once  converted  into  dark  lines.     The  same  experiment  may  be  tried  with  equal  effect 
with  potassium  and  other  metals. 

20.  The  daguerreotype  and  photograph  process  may  be  illustrated  by  strictly  following 
the  directions  contained  in  §§  293  and  294,  with  the  aid  of  a  good  camera  obscura,  tak- 
ing care  to  protect  the  prepared  plates  carefully  from  the  action  of  diffused  light.     The 
proportions  of  the  solutions  required  are  as  follows : 

1.  Collodion, — 5  or  6  grs.  of  gun  cotton,  to  1  oz.  of  mixture  of  1  part  of  alcohol  to  2 
of  ether,  then  add  2£  grs.  each  of  iodide  of  potassium,  and  iodide  of  cadmium. 

2.  Nitrate  of  Silver  Solution, — 480  grs.  of  crystallized  nitrate  of  silver,  to  2  oz.  of  water, 
with  addition  of  4  grs.  of  iodide  of  potassium,  or  cadmium. 

3.  Pvro-Gallic  Acid  Solution,—!  gr.  of  pyro-gallic  acid,  30  minims  of  alcohol,  30  min- 
ims of  glacial  acetic  acid,  2  grs.  of  citric  acid,  dissolved  in  1  oz.  of  water. 

4.  The  Hypo-Sulphite  of  Soda  Solution  should  be  saturated.     If  any  difficulty  be  en- 
countered, further  instruction  should  be  sought  from  some  experienced  photographer. 


CHAPTER  IV. 

THE    THIRD    CHEMICAL    AGENT: ELECTRICITY. 

STATICAL    ELECTRICITY  J   'GALVANIC     ELECTRICITY  ;    ELECTRO-MAGNET- 
ISM ;   MAGNETO-ELECTRICITY;    THERMO-ELECTRICITY;    ANIMAL 

ELECTRICITY  ;    THE  RELATIONS  OF  THE   CHEMICAL  AGENTS. 

• 

§  I.    Statical  Electricity. 

300.  Electricity.  The  third  of  the  three  great  imponder- 
able agents  by  which  the  action  of  chemical  affinity  is  controlled, 
and  which  is  either  produced  in  all  cases  of  chemical  action,  or 
has  a  powerful  effect  in  producing  them,  is  Electricity.  There 
are  two  different  states  in  which  electricity  is  manifested,  stati- 
cal and  galvanic.  The  former  is  electricity  in  a  state  of  repose  ; 
the  latter  is  electricity  in  movement.  Statical  electricity  is 
principally  produced  by  friction ;  it  accumulates  upon  the  sur- 
faces of  bodies,  and  exists  in  a  state  of  tension,  which  is  mani- 
fested by  sparks,  and  by  Ihe  attraction  which  it  exerts.  Gal- 

300.  What  is  the  third  imponderable?    In  what  two  states  does  it  exist?    Describe 
them. 


290  ITS    NATURE. 

vanic  electricity  is  principally  produced  by  chemical  action  ;  it 
£  ows  for  hours  in  a  steady  and  continuous  current ;  and  is  particu- 
larly distinguished  from  statical  electricity  by  its  chemical  effects, 
and  its  connection  with  magnetism. 

301.  The  nature  of  Electricity*    There  are  two  hypotheses 
in  regard  to  the  nature  of  this  powerful  agent  analogous  to  those 
which  have  been  mentioned  in  regard  to  the  nature  of  heat  and 
light.     The  first  regards  it  as  an  exceedingly  subtile  fluid,  so 
light  as  not  to  affect  the  most  delicate  balances ;  moving  with 
immense  velocity,  and  pervading  all  substances.     The  second 
regards  it  as  the  result  of  a  special  modification  made  in  the 
state  of  bodies,  depending  upon  a  peculiar  vibration  of  the  par- 
ticles of  matter  communicated  to  the  same  ether,  whose  undula- 
tions produce  heat  and  light.     The  latter  theory  is  the  one  which 
is  now  generally  received.     The  full  discussion  of  all  the  phe- 
nomena of  electricity  would  require  a  volume,  and  it  properly 
forms  a  part  of  the  sciences  embraced  in  Natural  Philosophy. 
We  are  concerned  with  it  here  only  ?o  far  as  it  is  connected 
with  chemical  phenomena,  and  as  a  knowledge  of  its  fundamen- 
tal facts  is  necessary  to  the  full  understanding  of  the  various 
chemical  processes  which  are  soon  to  come  under  our  notice. 
The  subject  of  galvanic  electricity  is  of  more  importance  to  the 
chemist  than  that  of  statical,  and  our  attention  will,  therefore, 
be  chiefly  directed  to  it.     The  fundamental  facts  on  which  the 
whole  science  of  statical  electricity  is  founded  may  be  stated  in 
a  few  words. 

302.  The  fundamental  facts  of  Statical  Electricity.     If  a 
piece  of  glass,  amber,  or  sealing-wax,  be  rubbed  with  the  dry 
hand,  dr  with  flannel,  silk,  or  fur,  and  then  held  near  small  light 
bodies,  such  as  straws,  hairs,  or  threads,  these  bodies  will  fly 
toward  the  glass,  amber,  or  wax,  thus  rubbed,  and,  for  a  moment, 
will  adhere  to  them.     The  substances  having  this  power  of  at- 
traction are  called  electrics,  and  the  agency  by  which  this  power 
is  exerted  is  called  electricity.     Some  bodies,  euch  as  certain 
crystals,  exert  the  same  power  when  heated,  and  others  become 
electric  by  pressure.     Although  these  are  the  simple  facts  on 
which  the  science  is  based,  yet  electricity  exhibits  a  vast  num- 
ber of  curious  and  interesting  phenomena,  depending  on  the 
variety  and  kind  of  machinery,  and  the  quantity  of  the  elcctri- 

301.  State  the  two  theories  in  regard  to  the  nature  of  electricity.  Which  is  now  gen- 
erally received?— 3^2.  State  the  fundamental  facts  of  electricity.  What  happens  when 
gla^s,  amher  and  sealing-wax  are  rubbed,  and  brought  near  small  pieces  of  pnper  ?  When 
.is  a  body  said  to  be  excited  with  electricity  ?  What  are  the  most  common  electrics  ? 


TIIK    SOURCES  291 

cal  influence  employed.  When  a  piece  of  glass,  or  other  elec- 
tric, has  been  rubbed,  so  as  to  attract  other  bodies,  it  is  said  to 
be  excited  with  electricity,  or  electrified,  and  it  is  found  that  many 
substances  are  capable  of  this  excitement,  when  managed  in  a 
peculiar  manner.  The  most  common  are  amber,  glass,  rosin, 
sulphur,  wax,  and  the  fur  of  animals. 

303.  The  sources  of  Electricity.  The  principal  source  of 
electricity  for  experimental  purposes,  is  friction.  Whenever 
two  surfaces  of  any  kind  are  rubbed  together,  one  becomes  ex- 
cited with  negative,  the  other  with  positive,  electricity.  This, 
however,  is  only  a  special  case  of  a  much  more  general  law,  for 
it  has  been  found  that  when  the  equilibrium  of  the  molecules  of 
any  body  is  disturbed,  a  development  of  electricity  takes  place. 
The  mere  compression  of  many  crystals  is  attended  by  electric 
action.  A  crystal  of  Iceland  spar,  if  compressed,  exhibits  signs 
of  electrical  excitement,  which  it  retains,  sometimes,  hours  and 
days.  The  same  is  true  of  fluor  spar,  of  mica,  of  arragonite, 
of  quartz,  and  several  other  substances.  Sometimes,  elevation 
and  depression  of  temperature  are  sufficient  to  develop  electri- 
city. This  is  especially  true  of  the  mineral,  tourmaline.  If  a 
crystal  of  this  substance  be  gently  heated,  it  becomes  powerfully 
electrified  while  the  temperature  is  rising,  one  extremity  being 
positively,  and  the  other  negatively  excited.  When  the  tem- 
perature becomes  stationary,  the  excitement  ceases  ;  as  the  crys- 
tal cools,  the  electric  excitement  returns,  but  the  polarity  is 
reversed ;  the  end  of  the  crystal  that  was  before  positive,  now 
becomes  negative.  The  temperature  should  not  rise  above 
300°.  The  electrical  excitement  of  the. crystal  may  be  shown 
by  its  power  of  attracting  and  repelling  light  substances  brought 
near  it.  Fracture  also  produces  electricity  ;  this  may  be  shown 
by  suddenly  breaking  a  stick  of  roll  sulphur.  The  rending  of 
crystals  along  the  line  of  clearage,  as  when  the  lamina?  of  a 
sheet  of  mica,  or  talc,  are  quickly  separated  in  a  dark  room, 
is  attended  with  a  feeble  electrical  light.  A  melted  substance, 
in  the  act  of  solidifying,  is  often  electric.  Melted  sulphur, 
solidifying  in  a  glass  vessel,  is  negatively  excited,  wh.le  the 
glass  becomes  positive.  Ice  is  also  often  electric.  This  is 
probably  due  to  molecular  movements.  Chemical  action  always 
produces  electricity.  Electricity  is  also  developed  in  the  pro- 
cess of  combustion  ;  carbon,  or- charcoal,  when  it  burns,  becomes 

3^3.  What  is  the  principal  source  of  electricity?  To  what  is  electrical  excitement,  in 
all  c,u=es,  thought  to  be  due?  What  is  the  effect  of  compressing  crystals?  01"  hc:tii:^ 
aad  cooling  tourmalhio  ?  Of  fracture?  Of  sblidLlcatiou  of  sulphur  ?  Of  couibustiau  J 


292 


OF    ELECTRICITY. 


negatively  electric,  while  the  carbonic  acid  which  it  forms,  is 
positive.  In  like  manner,  hydrogen,  when  it  burns,  is  negative, 
while  the  watery  vapor  produced  by  it  is  positive.  It  is  gaid, 
abo,  that  evaporation  is  a  source  of  electricity,  but  this  may  be 
regarded  as  a  case  of  chemical  action.  The  evaporating  sur- 
face is  negative,  while  the  vapor  is  positive.  The  atmosphere 
is  also  another  source  of  electricity,  not  only  during  storms,  but 
also  in  fine  weather.  Fogs,  snow,  and  rain,  are  almost  always 
charged  with  positive  electricity.  The  clouds  are  also  commonly 
highly  positive.  In  general,  all  these  sources  of  electricity  may 
be  resolved  into  the  movement  of  the  molecules  of  bodies,  and 
their  violent  separation  j  all  then  become  oppositely  electrified. 
Thus  electricity,  like  light  and  heat,  may  be  considered  as  due 
to  motion. 

334:.  Electrical  Attraction  and  Repulsion.  When  an  ex- 
cited electric,  like  a  rod  or  tube  of  glass,  which  has  been  vio- 
lently rubbed  with  a  piece  of  flannel,  is  presented  to  a  small 
ball  made  of  pith,  or  cork,  and  suspended  by  a  silk  thread,  the 
pith  ball  is  attracted  to  the  glass,  and  adheres  to  it  for  a  mo- 
ment, as  in  A,  Fig.  114.  Soon,  however,  it  is  repelled,  and 

occupies  the  portion  indi- 


Fig.  114. 


Electrical  Attraction. 


cated  by  B.  If  now,  to 
this  pith  ball,  thus  re- 
pelled, another  pith  ball 
be  presented,  this  is  first 
in  like  manner  attracted, 
and  then  repelled,  and  so 
on  with  a  succession  of 
similar  balls,  which  are 
each*  in  turn  attracted, 
and  repelled.  From  this 
experiment  we  draw  the 
following  conclusion,  that 
if  any  electric  be  excited 
by  friction,  it  will  first  at- 
tract, and  then  repel,  a 
light  substance  placed 
near  it,  and  that  this  light 
substance,  when  repelled, 
is  itself  in  a  state  of  dec- 


or evaporation  ?  What  is  the  electrical  state  of  the  clouds  ?  What  is  the  relation  of 
electricity  to  motion?— 304.  What  happens  when  an  excited  glass  rod  is  brought  m::tr  a 
pith  ball?  When  a  second  pith  ball  is  presented  to  the  first?  What  conclusion  do  wo 
draw  from  this  experiment 2 


TWO    KINDS    OF    ELECTRICITY. 


293 


trical  excitement,  similar  to  the  glass,  proved  by  the  fact  that 
it  first  attracts,  and  then  repels,  another  light  body  placed  near 
it.  A  metallic  rod  being  presented  to  the  electrified  pith  ball, 
it  will  lose  its  excitement  and  return  to  i's  natural  condition. 

305.  Two  bodies  similarly  electrified  repel  each  other.     If 
to  a  pith  ball,  thus  excited,  another  pith  ball,  excited  from  the 
same  piece  of  rubbed  glass,  be  presented,  they  will  mutually 
repel  each  other.     And,  in  like  manner,  if  a  rod  of  sealing-wax, 
or  sulphur,  be  violently  rubbed  with  a  piece  of  flannel,  and  then 
brought  near  to  a  pith  ball,  suspended  by  a  thread,  the  pith  ball 
will  at  first  be  attracted  by  the  sealing-wax,  and  then  repelled, 
and  will  be  found  to  have  become  excited  with  electricity,  simi- 
lar to  that  of  the  original  sealing-wax :  then,  if  to  this  pith 
ball  thus  excited,  a  second  pith  ball  be  presented,  that  has  been 
excited  by  the  same  piece  of  rubbed  sealing-wax,  we  shall  find 
that  these  two  pith  balls,  which  have  derived  their  electricity 
from  the  same  source,  will  mutually  repel  each  other.  <.\ 

306.  Two  bodies  differently  electrified  attract  each  other. 
—Two  kinds  cf  electricity,  Vitreous  and  Resinous.     But  if  to 
a  pith  ball,  excited  by  the  rubbed  glass,  there  be  presented  a 
pith  ball  that  has  been  excited  by  a  piece  of  rubbed  sealing- 
wax,  the  two  will  mutually  attract  each  other.     Hence  we  con- 
clude   that    while    bodies 


Fig.  115. 


The  Electroscope. 


similarly  electrified  repel, 
bodies  differently  electrified 
attract  one  another.  We 
also  conclude  that  there  is 
an  apparent  difference  be- 
tween the  electricity  pro- 
duced by  glass  when 
rubbed,  and  the  electricity 
produced  by  sealing-wax, 
and  it  is  usual  to  speak  of 
two  kinds  of  electricity, 
vitreous  and  resinous,  or 
positive  and  negative,  and 
they  are  often  denoted  by 
the  algebraic  signs  +  and 

307.  The  Electroscope. 

On    these    properties    is 


315.  What  is  the  effect  of  two  bodies  similarly  electrified  upon  each  other  ?— 306.  What 
eff  ct  have  two  bodies,  differently  electrified,  \ipon  each  other?  What  is  meaut  by  tb.a 
si^iis  -{-  and  — ? — 307.  Describe  the  electroscope. 


294  CONDUCTORS    AND    NON-CONDUCTORS. 

X 

founded  the  instrument  called  the  Electroscope,  intended  to 
indicate  the  presence  of  electricity  in  any  body,  and  the  kind 
of  it.  The  two  bits  of  gold  leaf,  n,  n,  in  the  accompanying  Fig. 
115,  which  are  both  connected  with  the  brass  head  of  the  instru- 
ment, are  similarly  electrified  when  any  excited  electric  is 
brought  near  to  them,  and  repel  each  other  more  or  le?s,  ac- 
cording to  the  degree  of  this  excitement.  Let  A  be  a  rod  of 
electrified  sealing-wax,  brought  near  to  the  knob,  c  ;  the  two 
bits  of  gold-leaf  will  be  electrified,  and  will  diverge  from  each 
other,  indicating  the  existence  of  electrical  excitement  in  A.  The 
kind  of  electricity  can  be  ascertained  in  the  following  manner. 
First,  electrify  the  gold  leaf  with  vitreous  electricity,  and  then 
see,  when  the  body  whose  electricity  it  is  wished  to  determine, 
is  brought  near  c,  whether  the  slips  continue  to  diverge,  or  come 
together  ;  if  the  former,  the  electricity  is  vitreous  ;  if  the  latter, 
it  is  resinous.  The  operation  of  this  instrument  will  be  more 
fully  explained  hereafter.  •o^fe^fc****'--:****. 

K  303.  Conductors  and  Non-conductors.— Insulation.  If,  in 
the  preceding  experiments,  the  pith  balls  be  suspended  from 
metal  chains,  having  a  direct  metallic  communication  with  the 
earth,  none  of  the  above  phenomena  Avill  be  manifested,  for  the 
electricity  will  pass  off  into  the  earth  as  soon  as  it  reaches  the 
balls,  while  the  electrical  excitement  invariably  makes  i'self  ap- 
parent if  these  be  suspended  from  silk  or  glass.  Hence  we 
conclude  that  some  substances  conduct  electricity  very  easily, 
and  do  not  permit  it  to  accumulate,  while  others  deny  it  a  pass- 
age. This  is  the  foundation  of  the  division  of  all  bodies  into 
conductors  and  non-conductors.  A  substance  is  said  to  be  in- 
sulated when  it  is  separated  from  all  direct  communication  with 
good  conductors  of  electricity  by  the  intervention  of  a  non-con- 
ductor, as  when  any  body  is  placed  upon  a  stool  with  glass  legs, 
or  a  metallic  rod  is  provided  with  a  glass  handle.  No  substance 

is  capable  of  being  permanent- 
Fig.  116.  ]v  electrified  which  is  not  a 

non-conductor  itself,  or  made 

Metallic  Rod  with  Glass  Handle.  ™     b7     insulation.       Thus,     ill 

Fig.  116,  we  have  a  bit  of 

brass  rod  with  a  glass  handle,  and  notwithstanding  the  conducting 
power  of  the  metal,  in  consequence  of  its  having  a  glass  handle, 
it  will,  when  rubbed,  exhibit  all  the  ordinary  marks  of  electrical 
excitement.  All  substances  exhibit  electricity  when  rubbed, 

Show  how  the  kirn!  of  electricity  may  be  detected.— 308.  What  is  meant  by  conduct- 
ors and  non-conductors  1    By  insulation  1 


THE    INDUCTION  295 

but  those  which  are  good  conductors  lose  it  immediately ;  con- 
sequently, there  are  no  signs  of  electrical  excitement,  except  the 
escape  be  prevented  by  insulation.  The  metals,  charcoal,  plum- 
bago, water,  and  substances  containing  water  in  a  liquid  state, 
and  therefore  more  or  less  damp,  are  conductors  of  electricity. 
Glass,  resins,  sulphur,  diamond,  dried  wood,  silk,  hair,  and  woo!, 
also  the  air  and  gases,  are  non-conductors ;  but  these  are  often 
rendered  conductors  by  the  presence  of  water.  For  this  reason, 
in  damp  weather,  many  electrical  experiments  can  not  be  per- 
formed, because  of  the  deposition  of  moisture  upon  the  surface 
of  insulators,  and  the  good  conducting  power  imparted  to  air  by 
watery  vapor. 

309.  Vitreous  electricity  can  not  be  produced  without  a 
correspondent  amount  of  resinous  electricity,  and  vice  versa. 
When  two  substances  are  rubbed  together,  both  vitreous  and 
resinous  electricity  are  developed,  the  rubber  being  charged 
with  one,  and  the  substance  rubbed,  with  the  other;  and  the 
presence  of  both  may  be  made  manifest  if  the  two  substances 
in  question  are  insulated.  Thus,  if  a  glass  rod  be  rubbed  with 
a  pie;-e  of  flannel,  while  the  glass  will  be  charged  with  vitreous 
electricity,  the  flannel  itself  will  be  charged  to  an  equal  degree 
with  resinous  electricity.  And  on  the  other  hand,  if  a  rod  of 
sealing-wax  be  rubbed  with  a  piece  of  dry  flannel,  while  the 
wax  will  be  excited  with  resinous  electricity,  the  piece  of  flan- 
nel will  be  charged  to  an  equal  degree  with  vitreous  electricity. 
It  is  impossible  to  produce  one  kind  of  electricity  without  at 
the  same  time  producing  an  equal  amount  of  the  opposite  kind. 
This  is  the  most  marked  peculiarity  possessed  by  electricity,  and 
this  is  the  reason  why  it  is  called  a  polar  force.  By  the  term 
polar  force,  is  meant  a  force  which,  whenever  it  is  produced, 
always  develops  an  equal  amount  of  force  over  against,  or  oppo- 
site to  itself,  just  as  the  poles  of  the  earth  are  opposite  to  each 
other.  The  peculiar  nature  of  a  polar  force  is  well  illustrated 
in  the  case  of  a  straight  bar  magnet,  or  a  common  magnetic 
needle,  while  one  end  is  excited  by  one  kind  of  magnetism,  and 
points  to  the  north,  the  other  end  is  excited  with  the  opposite 
kind  of  magnetism,  and  points  towards  the  south ;  and  the? e 
two  magnetic  forces  are  mutually  attractive  of  each  other.  In 
like  manner,  if  one  end  of  an  insulated  cylinder  of  brass  be 
kept  in  a  state  of  electrical  excitement  with  one  kind  of  electri- 

Mention  some  of  the  best  conductors.  Some  of  the  best  non  conductors.  What  ia 
the  effect  of  damp  Aveather  on  electrical  experiments? — 309.  Can  vitreous  electricity  be 
produced  without  the  manifestation  of  an  equal  amount  of  negative  ?  Why  is  electricity 
called  a  polar  force?  What  is  mean*  by  the  term  polar?  Give  an  illustration  of  this. 


296 


OF    ELECTRICITY. 


city,  the  other  extremity  will  be  excited  with  an  equal  amount 
of  the  opposite  kind.  This  polar  peculiarity  of  electricity  will 
become  more  apparent  as  we  proceed. 

310.  Induction  of  Electricity.  One  of  the  most  curious 
facts  connected  with  electricity  is,  the  power  that  a  highly  elec- 
trified body  has  of  throwing  all  other  bodies  near  it  into  a  sta'e 
of  electrical  excitement.  Thus,  an  electrified  glass  globe,  or 
other  body,  placed  in  the  centre  of  a  room,  will  produce  elec- 
trical excitement  in  all  objects  in  the  apartment,  and  if  they  be 
insulated,  sparks  may  be  drawn  from  them.  This  is  called  the 
induction  of  electricity.  When  careful  experiments  are  per- 
formed, it  is  found  that  if  the  body  in  question  be  charged  with 
vitreous  electricity,  it  will  induce  resinous  electricity  in  the  ex- 
tremities of  those  bodies  which  are  nearest  to  it,  while  vitreous 
electricity  will  be  manifested  on  those  ends  which  are  the  most 

Let  A  be  a  rod  of 
glass,  positively  elec- 
trified, and  let  it  be 
brought  near  the  me- 
tallic cylinder,  B,  in- 
sulated upon  a  stand 
of  glass.  B  will  im- 
mediately begin  to 
give  signs  of  electri- 
cal excitement,  and 
it  will  be  found,  on 
examination,  that  the 
end  of  B  nearest  A 
will  be  negatively, 
while  the  most  re- 
mote end  will  be 
positively  electri- 
fied. If  A  be  with- 
drawn, the  signs  of 
electrical  excitement 


remote.     This  is  illustrated  by  Fig.  117 

Fig.  117. 


Induction  of  Electricity. 


in  B  will  disappear.  If  it  be  again  brought  near,  they  will  re- 
appear. Should  a  connection  be  formed  between  the  remote 
end  of  B  and  the  earth,  the  positive  electricity  will  escape,  and 
B  will  then  contain  only  negative  electricity,  which  will  remain, 
after  A  is  withdrawn.  B  is  then  left  negatively  electrified  upon 

310.  What  is  meant  by  the  induction  of  electricity?  Is  the  electricity  induced  of  the 
same  kind  as  that  of  the  excited  body  ?  Explain  Fig.  117.  Is  it  possible  to  electrify  a 
body  without  the  actual  contact  of  the  excited  substance? 


SOLID    MATTER    ^7O    OBSTACLE. 


297 


its  insulated  s'atid,' and  if  any  body  be  now  brought  near  to  it, 
the  negative  electricity  will  escape  with  a  spark.  Thus  an  elec- 
trified body  drives  off  electricity  of  the  same  kind,  and  puts 
bodies  near  it  in  an  electrical  condition  opposite  to  itself.  The 
polar  relation  of  the  positive  or  vitreous  electricity,  and  the 
negative  or  resinous  electricity,  at  the  opposite  extremities  of 
the  cylinder,  B,  is  apparent ;  and  also  the  fact  that  one  kind  of 
electricity  can  not  be  developed  without  a  corresponding  devel- 
opment of  the  other. 

311.  The  intervention  of  solid  matter  no  obstacle  to  Induc- 
tion- This  effect  takes  place  even  through  glass  and  metallic  ob- 
stacles placed  in  the  way.  Thus,  in  Fig.  117,  if  a  plate  of  gla-s 
were  held  between  the  rod,  A,  and  B,  the  effect  would  be  the 
same.  And  so,  in  Fig.  118,  if  A  be  a  metallic  disk,  insulated 

upon    a    glass 

Fig.  118.  stand,   B  be   a 

plate  of  glass, 
and  c  be  an- 
other metallic 
disk,  and  if  A 
b  e  electrified 
positively  by 
an  electrical 
machine,  c  will 
be  immediately 
electrified  also, 
through  the 
glass,  B,  which 
will  oppose  no 
impediment  to 
the  process,and 

the  right  side  will  be  charged  with  positive  electricity,  while 
thfj  left  side  will  be  negative.  If  c  be  now  touched  on  the 
right  side  with  the  finger,  its  positive  electricity  will  escape, 
and  it  will  remain  negatively  electrified,  as  represented  in  the 
figure.  If,  instead  of  using  two  disks,  we  paste  a  piece  of  tin 
foil  on  one  side  of  a  frame  of  glass,  leaving  a  margin  of  an  inch 
on  every  side,  and  on  the  other  side  a  similar  piece  of  tin  foil, 
and  electrify  that  on  one  side,  the  foil  on  the  other  side  will  be 
charged  with  the  opposite  electricity,  if  a  connection  be  formed 
between  it  and  the  ground.  Or,  if  a  bottle  be  filled  with  cop- 


Solid  Matter  no  obstacle  to  Induction. 


311    Show  that  the  intervent'on  of  a.  solid  body  is  no  obsracle  to  induction.     Describe 
Fig.  118.     Show  how  induction  operates  i.i  the  case  of  the  electroscope. 


296 


OF    ELECTRICITY. 


city,  the  other  extremity  will  be  excited  with  an  equal  amount 
of  the  opposite  kind.  This  polar  peculiarity  of  electricity  will 
become  more  apparent  as  we  proceed. 

310.  Induction  of  Electricity.  One  of  the  most  curious 
facts  connected  with  electricity  is,  the  power  that  a  highly  elec- 
trified body  has  of  throwing  all  other  bodies  near  it  into  a  sta'e 
of  electrical  excitement.  Thus,  an  electrified  glass  globe,  or 
other  body,  placed  in  the  centre  of  a  room,  will  produce  elec- 
trical excitement  in  all  objects  in  the  apartment,  and  if  they  be 
insulated,  sparks  may  be  drawn  from  them.  This  is  called  the 
induction  of  electricity.  When  careful  experiments  are  per- 
formed, it  is  found  that  if  the  body  in  question  be  charged  with 
vitreous  electricity,  it  will  induce  resinous  electricity  in  the  ex- 
tremities of  those  bodies  which  are  nearest  to  it,  while  vitreous 
electricity  will  be  manifested  on  those  ends  which  are  the  most 
remote.  This  is  illustrated  by  Fig.  117.  Let  A  be  a  rod  of 

glass,  positively  elec- 
trifled,  and  let  it  be 
brought  near  the  me- 
tallic cylinder,  B,  in- 
sulated upon  a  stand 
of  glass.  B  will  im- 
mediately begin  to 
give  signs  of  electri- 
cal excitement,  and 
it  will  be  found,  on 
examination,  that  the 
end  of  B  nearest  A 
will  be  negatively, 
while  the  most  re- 
mote end  will  be 
positively  electri- 
fied. If  A  be  with- 
drawn, the  signs  of 
electrical  excitement 
in  B  will  disappear.  If  it  be  again  brought  near,  they  will  re- 
appear. Should  a  connection  be  formed  between  the  remote 
end  of  B  and  the  earth,  the  positive  electricity  will  escape,  and 
B  will  then  contain  only  negative  electricity,  which  will  remain 
after  A  is  withdrawn.  B  is  then  left  negatively  electrified  upon 


Induction  of  Electricity. 


310.  What  is  meant  by  the  induction  of  electricity  ?  Is  the  electricity  Induced  of  the 
same  kind  as  that  of  the  excited  body  ?  Explain  Fig,  111.  Is  it  possible  to  electrify  a 
body  without  the  actual  contact  of  the  excited  substance? 


SOLID    MATTER    NO    OBSTACLE. 


297 


its  insulated  s'ancVand  if  any  body  be  now  brought  near  to  it, 
the  negative  electricity  will  escape  with  a  spark.  Thus  an  elec- 
trified body  dri\7es  off  electricity  of  the  same  kind,  and  puts 
bodies  near  it  in  an  electrical  condition  opposite  to  itself.  The 
polar  relation  of  the  positive  or  vitreous  electricity,  and  the 
negative  or  resinous  electricity,  at  the  opposite  extremities  of 
the  cylinder,  B,  is  apparent ;  and  also  the  fact  that  one  kind  of 
electricity  can  not  be  developed  without  a  corresponding  devel- 
opment of  the  other. 

311.  The  intervention  of  solid  matter  no  obstacle  to  Induc- 
tion- This  effect  takes  place  even  through  glass  and  metallic  ob- 
stacles placed  in  the  way.  Thus,  in  Fig.  117,  if  a  plate  of  gla;s 
were  held  between  the  rod,  A,  and  B,  the  effect  would  be  the 
same.  And  so,  in  Fig.  118,  if  A  be  a  metallic  disk,  insulated 

upon    a    glass 

Fig.  118.  stand,   B  be  a 

plate  of  glass, 
and  c  be  an- 
other metallic 
disk,  and  if  A 
b  e  electrified 
positively  by 
an  electrical 
machine,  c  will 
be  immediately 
electrified  also, 
through  the 
gla^s,  B,  which 
will  oppose  no 
impediment  to 

Solid  Matter  no  obstacle  to  Induction.  ^he  prOCCSS  and 

the  right  side  will  be  charged  with  positive  electricity,  while 
tho  left  side  will  be  negative.  If  c  be  now  touched  on  the 
right  side  with  the  finger,  its  positive  electricity  will  escape, 
and  it  will  remain  negatively  electrified,  as  represented  in  the 
figure.  If,  instead  of  using  two  disks,  we  paste  a  piece  of  tin 
foil  on  one  side  of  a  frame  of  glass,  leaving  a  margin  of  an  inch 
on  every  side,  and  on  the  other  side  a  similar  piece  of  tin  foil, 
and  electrify  that  on  one  side,  the  foil  on  the  other  side  will  be 
charged  with  the  opposite  electricity,  if  a  connection  be  formed 
between  it  and  the  ground.  Or,  if  a  bottle  be  filled  with  cop- 


311    Show  that  the  intervent:on  of  a  solid  body  is  no  obstacle  to  induction.     Describe 
Fig.  118.     Show  ho.v  induction  operates  i.t  the  case  of  the  electroscope. 


208  THEORY    OF    INDUCTION. 

per  leaf,  or  have  tin  foil  pasted  on  the  inside,  and  the  outside  be 
covered  with  tin  foil  extending  over  the  bottom,  and  three- 
fourths  of  the  body  of  the  bottle,  and  a  connection  be  formed 
between  the  inside  and  an  electrical  machine,  the  outer  side 
will  also  be  electrified  with  the  opposite  electricity.  This  is 
the  arrangement  of  the  famous  Leyden  jar.  In  the  case  of 
the  Electroscope,  Fig.  115,  the  rod  A,  of  sealing-wax  being 
negatively  electrified  when  brought  near  to  c,  induces  in  the 
knob  positive  electricity,  as  is  seen  in  the  figure,  and  negative 
electricity  in  the  leaves  of  gold  ;  but  both  being  similarly  elec- 
trified, they  repel  each  other  in  proportion  to  the  degree  of  elec- 
trical excitement  in  A,  until  they  touch  the  metallic  slips,  «,  «, 
on  each  side  connected  with  the  earth.  At  the  moment  of  con- 
tact, the  negative  electricity  escapes,  and  there  is  nothing  but 
positive  electricity  left  in  the  knob,  c,  and  the  leaves.  At  first, 
these  fall  together,  but  almost  immediately  begin  to  repel  each 
other  under  the  influence  of  the  positive  electricity  with  which 
they  are  now  both  affected. 

312.  The  theory  of  Induction.  The  difference  between  the 
conduction  and  induction  of  electricity  consists  in  the  mode  in 
which  the  electrical  influence  is  propagated  from  atom  to  atom, 
through  bodies,  so  as  to  exert  an  effect  at  a  considerable  distance. 
If,  when  an  electrified  body  is  brought  near  to  a  body  which  is  in 
its  natural  state,  there  be  an  instantaneous  passage  of  the  electri- 
city through  the  particles  of  the  second  body,  the  process  is  said 
to  be  conduction,  and  the  body  in  question  is  called  a  good  con- 
ductor. If,  however,  there  is  riot  an  instantaneous  transmission 
of  the  electrical  influence  through  the  particles  of  the 
Fig.  119.  second  body$  but  a  certain  amount  of  resistance  of- 
fered  to  the  passage  of  the  electricity,  the  particles 
become  polarized  by  induction  ;  and  as  each  particle 
that  is  electrified  induces  electricity  in  those  near  it, 
Q  Q  Q#  anc^  throws  them  into  a  polar  state,  the  effect  may 
©  Q  ttj  ^e  ProPagated  to  a  great  distance.  This  is  well 
a  illustrated  in  Fig.  119.  Let  P  represent  any  body 
charged  with  positive  electricity,  and  abed  rows  of 
particles  of  air,  intermediate  between  P  and  a  second 
conductor,  N.  Air,  as  we  know,  is  a  poor  conductor 
of  electricity,  and  opposes  some  impediment  to  its 
passage;  consequently,  the  particles  of  air  between 
P  and  N,  all  become  polarized  ;  i.  e.,  their  electrical 


312.  State  the  theory  of  induction.    Show  that  it  is  accomplished  by  a  process  of 
polarization.    Describe  'Fig.  119. 


CONFINED    TO    THE    EXTERNAL    SURFACE. 


299 


state  is  disturbed,  and  the  negative  electricity  in  each  is  drawn 
towards  ihe  positively  charged  body,  p,  while  the  positive  elec- 
tricity in  each  particle  is  driven  to  the  opposite  pole  and  turned 
towards  the  conductor,  N.  The  body,  N,  is  also  similarly  affected, 
its  negative  electricity  being  strongly  attracted  towards  the  posi- 
tive electricity  of  the  particles  in  d,  immediately  contiguous  to 
it,  and  its  positive  electricity  being  repelled  to  the  greatest  pos- 
sible distance.  This  state  of  things  will  continue  as  long  as  p 
remains  in  its  position  ;  but  if  that  body  be  removed,  the  state 
of  polar  tension  will  cease,  and  the  electricity  of  N,  and  the  par- 
ticles of  air  will  return  to  its  natural  state. 

313-  Electricity  confined  to  the  external  surface  of  Bodies* 
This  may  be  proved  by  the  following  experiment  devised  by  Cou- 
lomb. A  hollow  sphere  of  brass,  Fig.  120,  is  mounted  upon  a 

stand  of  glass,  and  pierced 

Fig-  120.  with    a    circular    aperture. 

It  is  highly  "electrified  by 
contact  with  an  electrical 
machine,  and  its  inner  sur- 
face is  touched  by  a  stick  of 
glass  or  gum  lac,  tipped  with 
a  small  bit  of  brass,  c.  This 
piece  of  brass  is  then  applied 
to  the  gold  leaf  electroscope, 
Fig.  115,  and  no  divergence 


of  the  leaves  can  be  observed. 
The  bit  of  brass  is  next  ap- 
plied to  the  outside  surface  of 
the  globe,  and  then  to  the 
same  electroscope,  when  a 
manifest  divergence  of  the 
leaves  is  seen.  Hence  we 
conclude  that  there  was  no 
accumulation  of  electricity 
except  upon  the  outside  sur- 
face. This  fact  may  bo 
proved  by  other  experiments  of  a  still  more  satisfactory  charac- 
ter. It  is  found,  al.-:o,  that  smoothness  of  the  external  surface 
has  a  great  effect  in  retaining  electricity  and  preventing  it  from 
escaping,  while  points  and  sharp  edges  greatly  favor  its  escape. 
For  this  reason  the  prime  conductors  of  electrical  machines,  and 


Electricity  confined  to  the  Surface. 


3T.3.  Show  that  electricity  is  confined  to  .the  external  surface  of  bodie*.     What  is  tiio 
effect  of  the  smoothness  and  roughness  of  surfaces  on  the  escape  of  electricity  ? 


300  THEORIES    OF    ELECTRICITY. 

all  the  parts  of  Leyden  jars,  should  be  made  as  smooth  as  pos- 
sible. On  the  same  principle,  perfectly  smooth  surfaces,  brought 
near  to  highly  charged  electrified  bodies,  receive  electricity  from 
them  with  great  difficulty  and  always  with  a  spark  and  shock, 
while  edges  and  points  will  receive  it  from  a  distance,  and 
silently,  without  either  spark  or  noise.  This  is  the  principle  on 
which  lightning  rods  are  constructed.  They  disarm  the  highly 
electrified  clouds  from  a  distance,  noiselessly  and  quietly. 
These  rods  were  first  set  up  by  Dr.  Franklin,  shortly  after  he 
made  his  great  discovery  of  the  identity  of  lightning  and  elec- 
tricity, by  means  of  a  kite  raised  in  a  thunder  storm,  in  the 
neighborhood  of  Philadelphia. 

314.  Theories  of  Electricity.  Two  different  theories  have 
been  proposed  to  account  for  the  phenomena  of  electricity,  that 
of.  Dr.  Franklin,  and  that  of  Dufay.  To  account  for  electrical 
phenomena,  Dr.  Franklin  supposed,  as  above  stated,  that  all 
terrestrial  things  had  a  natural  quantity  of  that  subtile  fluid,  but 
that  its  effects  became  apparent  only  when  a  substance  contained 
more  or  less  than  the  natural  quantity,  and  that  this  state  is  pro- 
duced by  the  friction  of  an  electric.  Thus,  when  a  piece  of  glass  is 
rubbed  by  the  hand,  the  equilibrium  is  destroyed,  in  consequence 
of  the  electrical  miid  passing  from  the  hand  to  the  glass,  so  that 
now  the  hand  contains  less,  and  the  glass  more,  than  their  ordi- 
nary quantities.  These  two  states  he  called  positive  and  nega- 
tive, implying  the  presence  and  absence  of  the  electrical  fluid. 
If  now  a  conductor  of  electricity,  such  as  a  piece  of  metal,  be 
made  to  touch  a  positive  body,  or  brought  near  it,  the  ac- 
cumulated fluid  will  leave  this  body  and  pass  to  the  conductor, 
which  will  then  contain  more  than  its  natural  quantity  of  the 
fluid.  But  if  the  conductor  be  made  to  touch  a  negative  body, 
then  it  will  impart  a  share  of  its  own  natural  quantity  of 
the  fluid  to  that  body,  and  consequently  will  contain  less  than 
usual.  Also,  when  one  body,  positively,  and  another  nega- 
tively electrified,  are  connected  by  a  conducting  substance,  the 
fluid  rushes  from  the  positive  to  the  negative  body,  and  the 
equilibrium  is  restored.  This  theory,  originally  invented  ly 
Dr.  Franklin,  will  account  satisfactorily  for  nearly  every  elec- 
trical phenomenon.  There  is,  however,  another  theory,  that  of 
Dufay,  wh:ch  is  also  very  generally  received.  This  theory  sup- 
poses that  there  are  two  kinds  of  electricity,  which  are  termed 
the  vitreous  and  resinous,  correspond'ng  with  the  positive  and 

Explain  the  principle  of  the  lightning-rod.— 314   What  is  the  theory  of  Franklin  ?    Of 
Dufay  ?    Which  is  preferred  ? 


THE    ELECTRICAL  301 

negative  of  Franklin.  This  supposition  is  founded  on  the  fact, 
that  when  two  pith  balls,  or  other  light  bodies,  near  together,  are 
bath  touched  by  an  excited  piece  of  glass,  or  sealing-wax,  they 
repel  each  other.  But  if  one  of  the  balls  be  touched  by  the 
glass,  and  the  other  by  the  wax,  they  will  attract  each  other. 
Hence,  Dufay  concluded  that  electricity  consists  of  two  distinct 
fluids,  which  exist  together  in  all  bodies  ;  that  these  two  fluids 
attract  each  other,  but  that  they  are  separated  during  the  excita- 
t'on  of  an  electric,  and  that  when  thus  separated,  and  transferred 
to  non-electrics,  as  to  the  pith  balls,  the  mutual  attraction  of  the 
two  electricities  cause?  the  balls  to  rush  towards  each  other. 
The  electricity  corresponding  with  the  positive  of  Franklin,  is 
called  vitreous,  because  it  is  obtained  from  glass,  while  the  other 
is  called  resinous,  because  it  is  obtained  from  wax:  and  resin. 
In  respect  to  the  merit  of  these  two  theories,  we  can  only  say 
here,  that  while  Franklin's  is  the  most' simple  and  accounts 
equally  well  for  nearly  all  electrical  phenomena,  the  preponder- 
ance of  opinion  is  at  the  present  time  in  favor  of  the  theory  of 
the  polar  character  of  electricity.  It  is  regarded  not  as  a  fluid, 
but  as  a  force,  which  acts  at  the  same  moment  in  opposite  direc- 
tions. 

315.  Development  of  large  quantities  of  Electricity  .—The 
Electrical  XHachine-  When  large  quantities  of  electricity  are 
desired,  it  is  obtained  by  means  of  the  friction  of  a  large  sur- 
face of  some  non-conducting  electric,  such  as  g'ass ;  this  is 
accomplished  by  means  of  what  are  called  Electrical  Machines. 
There  are  two  kinds,  called  the  cylinder  and  plate  machines, 
depending  on  the  form  of  the  glass  used  to  excite  the  electricity. 
The  plate  machine  is  considered  much  the  best,  since  bo:h  sides 
are  exposed  to  electrical  friction,  while  in  the  cylinder  machine 
only  the  outside  can  be  excited.  The  plate  machine  is  repre- 
sented in  Fig.  121.  It  consists  of  a  plate  of  glass,  F,  F,  turning 
on  an  axis  of  wood,  by  the  handle,  M,  and  supported  by  a  frame 
fixed  to  a  platform,  also  of  wood.  On  opposite  sides  are  two 
cushions  of  leather,  made  to  press  against  the  plate  by  springs. 
From  D,  or  some  other  part  connected  with  the  rubbers,  a  rod  de- 
scends to  the  ground  as  a  conductor  of  electricity  to  the  machine. 
The  electrical  fluid  accumulates  on  the  surface  of  the  prime 
conductors,  c,  C,  which  are  insulated  by  glass  supports  in  order 
to  prevent  the  escape  of  the  fluid.  By  means  of  such  a  ma- 
chine, especially  if  the  cushions  arc  covered  by  soft  mercurial 

315.  Describe  the  electrical  machine. 


302 


MACHINE. 
Fig.    121. 


The  Electrical  Machine. 

amalgam,  large  quantities  of  electricity  may  be  collected. 
On  turning  the  plate,  sparks  are  seen  to  pass  from  its  surface  to 
the  prime  conductors,  being  attracted  by  sharp  points  of  brass 
wire,  which  issue  from  their  smooth  and  brightly  poll-  lied  sur- 
faces. A  plate  of  two  feet  in  diameter  is  sufficient  for  all  ordi- 
nary purposes,  but  they  are  often  made  much  larger,  requiring 
the  strength  of  several  men  to  turn  them. 

.  316.  The  Leyden  Jar.  An  indispensable  companion  to  the 
electrical  machine  is  the  Leyden  Jar,  so  called  from  having 
been  invented  at  Leyden,  in  Holland.  It  depends  for  its  action 

316.  Describe  the  Leyden  jar. 


THE  LEYDEN  JAR. 


303 


upon  the  principle  of  the  induction  of  electricity,  above  ex- 
plained. It  is  necessary  to  bear  in  mind  that  glass  is  no  impedi- 
ment to  the  induction  of  electricity  by  a  highly  charged  electric, 
Tiie  apparatus  is  delineated  in  the  accompanying  Fig.  122.  It 
consists  of  a  glass  jar,  coated  both  inside  and  out- 
side with  tin  foil,  except  a  part  around  the  top,  as 
shown  in  the  figure.  The  inside  is  sometimes  also 
filled  with  gold  or  copper  leaf.  Through  a  var- 
nished wooden  stopper,  or  through  an  ordinary 
cork,  a  wire  having  a  knob  at  its  top  is  passed,  and 
extends  to  the  inside  coating.  Now,  if  either  posi- 
tive or  negative  electricity  be  communicated  to  the 
knob,  it  is  immediately  diffused  over  the  whole  of 
the  inside  coating,  and  by  its  inductive  influence 
the  outside  coating  takes  on  the  opposite  kind. 
When  in  this  state,  the  two  coatings  being  oppo- 
sitely electrified,  the  jar  is  said  to  be  charged. 
The  more  the  inside  is  charged,  the  more  also,  and  io  the  eame 
degree,  is  the  outside  also  charged.  In  this  stale,  as  soon  as  a 

commun'cation  is  estub- 

Fig.  123.  lislied  between  the  in- 

side and  the  outside 
coatings,  the  two  elec- 
tricities being  mutually 
attracted,  rush  together 
with  a  bright  flash  and 
loud  report,  and  the 
equilibrium  is  at  once 
restored.  The  dis- 
charge may  be  effected 
through  a  short  metallic 
circuit,  as  in  the  accom- 
panying Fig.  123,  or 
through  a  long  chain,  cr 
through  the  fingers,  or 
through  a  larger  part 

of  the  body,  the  outside  of  the  jar  being  grasped  in  one  hand, 
and  the  knob  touched  with  the  fingers  of  the  other  hand ;  or  in 
fine,  several  peivons  may  form  a  circuit,  by  taking  hold  of  hands, 
and  the  one  at  one  extreme  touching  the  outside  coating,  while 
the  one  at  the  other  touches  the  knob.  All  will  feel  the  shock 


Discharge  of  a  Leyden  Jar. 


How  roav  it  be  discharged? 

13 


304 


THE  THEORY  OF  THE  LEYDEN  JAE. 


at  the  same  instant.  It  is  usual  to  charge  the  jar  from  the  elec-- 
trical  machine,  but  it  may  also  be  charged  from  the  Electro- 
phorus,  an  instrument  to  be  presently  described. 

317.  Mode  of  charging  the  Leyden  Jar.  While  the  jar  is 
receiving  the  charge,  it  must  not  be  insulated,  i.  e.,  the  outside 
must   communicate,  through  some    good  conductor,   with   the 
earth.     As  the  positive  fluid  collects  on  the  inside,  the  outside 
becomes  negative,  by  the  expulsion  of  the  positive   fluid  natu- 
ral  to  it,    and   the   accumulation  of  the  negative  fluid  in  its 
stead,  drawn  from  the  earth.     But  if  the  outside  is  insulated, 
these  transfers  to  and  from  it  can  not  take  place,  and  therefore 
the  jar  can  not  become  charged. 

318.  The  theory  of  the  Leyacn  Jar.    As  the  Leyden  jar  is 
charged  by  induction,  the  theory  of  the  process  is  the  same  as 
that  given  for  every  process  of  induction,  viz.,  that  it  is  accom- 
plished by  the  polarization  of  the  particles  of  an  imperfect  elec- 
trical conductor.     Let  No.  1,  in  Fig.  124,  indicate  a  section  of 

the  glass  side  of  a  Ley- 
Fig.  124.  <jen  jar  in  its  natural 
or  uncharged  state ;  all 
the  particles  composing 
it  are  represented  as  in 
an  indifferent  electrical 
condition.  No.  2  rep- 
resents a  section  of  a 
similar  jar  in  its  charged 
condition.  The  inside 
surface,  I,  having  been 
connected  with  the 
prime  conductor  of  an 
electrical  machine,  is  charged  with  positive  electricity.  The 
effect  of  this  has  been  to  expel  all  the  positive  electricity  from 
the  row  of  particles  nearest  the  inside  surface,  and  to  force  it  into 
the  next  row ;  this  has  compelled  the  positive  electricity  of  this 
row  to  take  refuge  in  the  third  row,  the  positive  electricity  of 
which  it  has  expelled  and  driven  into  the  fourth  row ;  and  this 
in  turn  has  been  compelled  to  escape  from  the  jar  by  the  agency 
of  the  conductor  connecting  it  with  the  ground,  leaving  the 
outside  of  the  glass  in  a  highly  excited  negative  state,  while 
the  inside  is  maintained  in  a  highly  excited  positive  state  by  its 


O33O 
033« 
033* 


033* 
033« 

2 


Theory  of  the  Leyden  Jar, 


317.  Why  can  the  Leyden  jar  not  be  charged  if  it  be  insulated  ?— 318.  State  the  theory 
of  the  Leydeii  jar. 


THE    ELECTROPHORUS. 


305 


connection  with  the  electrical  machine.  Let  the  jar  be  now 
disengaged  from  the  electrical  machine,  and  the  two  surfaces 
tli us  oppositely  excited  be  connected  through  the  agency  of  a 
metallic  conductor,  and  the  equilibrium  will  be  restored  by  (he 
sudden  rush  of  the  two  charges  towards  each  other,  accompa- 
nied by  a  shock  and  a  spark  of  unusual  brilliancy. 

319.  The  Slectrophorus.  This  is  an  instrument  for  readily 
obtaining  small  quantities  of  electricity.  It  consists  of  a  plate 
of  resin  from  nine  to  twelve  inches  in  diameter  contained  in  a 
shallow  dish  of  metal,  and  a  metallic  disk,  A,  a  little  smaller 
than  the  plate  of  resin,  provided  with  a  glass  handle.  See  Fig. 
125.  To  charge  the  Electrophorus,  the  plate  of  resin  is  briskly 

Fig.  125. 


TJie    E'ectrophorus. 

rubbed  with  a  piece  of  warm  dry  flannel,  or  struck  several 
times  with  a  dry  silk  handkerchief,  folded  up  for  the  purpose, 
or  by  the  skin  of  a  cat,  by  means  of  which  negative  electricity 
is  excited.  If  now  the'  plate  of  metal  be  brought  down  upon 
the  resin,  its  lower  surface,  under  the  influence  of  induction, 
will  become  positive,  while  its  upper  surface  will  be  negative. 
Let  the  upper  surface  be  now  touched  with  the  finger,  Fiy.  125, 

319.  Describe  the  electrophorus. 


306 


THE    HYDRO-ELECTRIC 


the  negative  electricity  will  be  withdrawn,  and  the  plate  wilt 
become  wholly  charged  with  positive  electricity  to  sucli  a  degree 
that  sparks  can  readily  be  obtained  from  it.  This  electricity 
being  merely  the  result  of  induction,  the  resin  has  lost  none  of 
that  produced  by  the  original  rubbing,  and  the  process  may  be 
repeated  many  times  without  any  additional  friction.  This 
instrument  is  of  great  use  in  the  laboratory,  for  exploding  gase- 
ous mixtures.  -^ 

320.  The  Hydro- Electric  machine.  Electricity  may  also 
be  generated  by  the  friction  of  steam  of  very,  high  pressure 
against  the  sides  and  edges  of  an  aperture,  through  which  it  is 
violently  rushing.  The  apparatus  is  called  the  Hydro-Electric 
machine ;  Fig.  126.  A  strong  iron  boiler  and  furnace,  arranged 

Fig.  126. 


The  Hydro  ""Electric  Maehlne. 


320    Describe  the  hydro-electric  machine.     To  what  is  the  electricity  produced  by  this 
process  really  due  ? 


MACHINE. 


307 


upon  the  plan  of  the  boiler  of  a  locomotive,  is  mounted  upon 
four  stout  glass  insulators,  well  varnished.  The  boiler  is  pro- 
vided with  a  safety  valve,  s,  and  with  a  gauge  for  showino-  the 
water  level,  o  ;  B  represents  the  smoke  chimney ;  A,  a  row  of 
apertures  for  the  escape  of  steam ;  c,  a  stop-cock,  commanding 
these  apertures.  The  apertures  are  all  lined  with  wood  or 
ivory,  and  are  each  provided  with  a  partition  nearly  closing  the 
passage,  for  the  purpose  of  increasing  the  friction  of  the  steam 
as  it  escapes  ;  one  of  them  is  shown  in  section  at  M.  p  is  a  col- 
lection of  bright  metallic  points,  for  the  purpose  of  collecting 
the  electricity,  and  these  are  mounted  upon  a  movable  stand. 
The  pressure  of  steam  required  is  about  90  Ibs.  to  the  square 
inch.  On  opening  the  stop-cock,  the  steam  rushes  out  with 
great  fury,  a  portion  is  condensed  into  globules  of  water,  and 
these,  as  they  are  carried  forward,  are  pressed  violently  against  the 
sides  of  the  apertures.  This  friction  decomposes  their  natural 
electricity,  the  negative  remaining  on  the  jets,  while  the  positive  is 
carried  out  by  the  steam  and  deposited  upon  the  conductor,  p.  The 
interior  of  the  tubes  plays  the  part  of  the  rubber  of  the  ordinary 
machine,  while  the  steam  acts  as  the  glass  plate.  Sparks  have 
been  obtained  from  this  machine  at  the  distance  of  22  inches. 

321,    The    effects  of 

Fig.  127.  Electricity.       These    are 

marked  and  powerful,  and 
may  be  classified  as  Phys- 
iological, Luminous,  Calo- 
rific, Mechanical,  Chemical, 
and  Magnetic.  The  shock 
produced  by  the  discharge 
of  a  Leydeii  jar  is  an  in- 
stance of  the  physiological 
effects.  The  bright  spark, 
and  the  flashes  of  light, 
that  may  be  drawn  from 
the  electrical  machine  in 
the  dark,  show  its  luminous 
effects.  Its  calorific  effects 
may  be  shown  by  the  in- 
flammation of  gunpowder, 
and  of  alcohol,  when  a  powerful  discharge  is  passed  through 
them  from  the  Leyden  jar,  Fig.  127,  and  by  the  expansion  of 


Inflammation  of  Alcohol  by  Electricity. 


321.  State  the  effects  of  electricity. 


308 


THE    EFFECTS    OF 


air  in  a  confined  vessel,  Fig.  128.     The  expansion  is  indicated 

by    the    rising    of    the 


Fig.    128. 


Expansion  of  Air  from  an  Electric  Discharge. 


water  in  the  glass  tube, 
as  soon  as  the  discharge 
from  the  Ley den  jar 
takes  place.  Its  me- 
chanical effects  are  ex- 
hibited by  the  splitting 
of  plates  of  glass, 
through  which  a  charge 
is  transmitted,  by  the 
piercing  of  a  card,  Fig. 
129,  and  by  the  gen- 
erally destructive  results 
of  severe  lightning.  Its 
chemical  effects  are 
shown  by  the  decompo- 
sition of  many  com- 
pound bodies,  and  its 
powerful  influence  in 
determining  chemical 
combination.  When  a 
succession  of  electric 
discharges  from  a  pow- 
erful electric  machine 


is  sent  through  pure  water  contained  in  a  glass  tube,  by  means 
of  gold  or  platinum  conductors,  which  nearly  touch  each  other 
in  the  liquid,  the  water  is  decomposed,  and  resolved  into  its  two 
elements,  hydrogen  and  oxygen,  which  immediately  assume  the 
gaseous  state,  and  form  a  collection  of  gas  at  the  upper  end  of 
the  tube.  This  experiment  was  performed  in  1798,  in  Holland, 
and  it  conclusively  shows  the  power  of  electricity  in  effecting 
chemical  decomposition.  It  is  equally  efficacious  in  bringing 
about  chemical  combinations,  for  if  this  mixture  of  the  two  gases 
be  introduced  into  a  tube,  closed  at  the  upper  end,  Fig.  130, 
over  water,  so  arranged  that  an  electric  charge  can  be  passed 
through  it  by  means  of  the  wires  t  and  c,  and  one  single  spark 
be  transmitted,  the  oxygen  and  hydrogen  will  re-unite  with  a 
brilliant  flash  of  light,  great  commotion  result,  and  a  minute  por- 
tion of  water  will  be  formed.  If  the  end  of  such  a  tube  were 
to  be  corked,  and  then  the  tube  removed  from  the  water,  on  the 


Give  illustrations  of  these  effects. 


ELECTRICITY. 
Fig.  129. 


309 


Card  Split  by  an  Electric  Discliarge. 
Fig.    130. 


C/iemical  Effect  of  Electricity. 


passage  of  the 
spark,  a  loud  ex- 
plosion would 
take  place.  This 
is  by  no  means 
the  only  instance 
of  the  chemical 
power  of  this 
wonderful  agent. 
Chlorine  and  hy- 
d  r  o  g  e  n  can  be 
made  to  unite  in 
the  same  manner, 
with  an  explosion 
forming  chloro- 
hydric  acid :  illu- 
minating gas,  and 


I  oxygen,  forming  water  and  carbonic  acid:  and  the  same  with 
j  many  other  gases.  Finally,  electricity  produces  powerful  mag- 
\  netic  effects.  If  a  succession  of  strong  electric  shocks  be  trans- 
i  mitted  through  a  steel  needle,  it  becomes  a  permanent  magnet. 


310  ELECTRICAL    EXPERIMENTS.  1 

The  needle  should  be  placed  upon  some  non-conducting  mate- 
rial, on  a  plate  of  copper,  about  two  inches  in  length,  and  at 
right  angles  to  the  course  of  the  current.  Both  chemical  and 
magnetic  effect  is  much  more  powerfully  exerted  by  the  galvanic 
current. 

Experiments  : — Electricity. 

I 

1.  To  show  that  electricity  may  be  excited  by  friction,  rub  a  bit  of  amber,  a  glass  rod, 
ft  stick  of  sealing-wax,  and  rod  of  sulphur,  with  a  piece  of  silk,  and  hold  each  in  turn 
near  a  pith  ball,  suspended  by  a  silk  thread  from  an  insulated  hook,  as  in  Fig.  114 ,  the 
ball  will,  in  every  case,  be  first  attracted,  and  then  repelled. 

2.  To  show  that  compression  produces  electricity,  press  in  the  hand  a  piece  of  Iceland 
spar,  and  then  apply  it  to  the  electroscope,  Fig.  115  ;  the  leaves  will  immediately  d  verge. 
Rub  together  two  round  uncut  stones  or  quartz,  chalcedony,  and  cornelian,  and  a  strong 
phosphoric  rght  and  odor  will  be  produced. 

3.  That  elevation  and  diminut  on  of  temperature  produce  electricity,  may  be  shown 
by  dipping  the  mineral  tou  maline  into  boiling  water,  and  then  apphing  it  to  the  elec- 
troscope ;  as  it  cools,  the  leaves  will  diverge.     This  will  cont  nue  during  all  the  time  of 
cooling,  and  one  end  of  the  crystal  will  exhibit  positive,  and  the  other  negative  electricity 

4.  That  fracture  produces  electricity  may  be  shown  by  suddenly  breaking  a  stick  of 
roll  sulphur,  and  applying  either  piece  to  the  knob  of  the  electroscope,  or  holding  it  near 
a  pith  ball ;  also,  by  warming  a  piece  of  talc,  splitting  it  rapidly,  and  holding  one  of  the 
pieces  near  the  electroscope  ;  also,  by  splitting  mica,  and  ty-  doubling  a  large  card,  aud 
tearing  it  across. 

5.  Melt  sulphur,  and  pour  it  into  a  wine  glass  ;  both  will  become  electrified. — the  sul- 
phur negatively,  and  the  glass  positively,  and  first  attract,  and  then  repel,  a  pith  ball. 

6.  To  show  that  electricity  is  developed  in  the  process  of  combustion,  support  a  piece 
of  brass  upon  the  top  of  a  delicate  gold  leaf  electroscope,  in  such  a  way  that  one  end 
will  project  considerably  over  the  side  of  t  e  instrument ;   then  take  a  cylindrical  piece  of 
cnarcoal,  with  flat  ends,  2  inches  high,  and  1  inch  in  diameter.     Place  this  piece  of  char- 
coal vertically  about  3  inches  below  the  projecting  brass  plate.     The  charcoa  must  com- 
municate with  the  ground,  and  be  lighted  at  the  centre  of  the  upper  end,  taking  care 
that  the  fire  does  not  reach  t  e  sides.     A  current  of  carbonic  acid  gas  rises  and  strikes 
a  >ainst  the  plate,  and  in'  a  few  minutes  the  electroscope  will  show  signs  of  electric  ex- 
citement.    This  is  a  delicate  experiment. 

7.  That  evaporation  produces  electricity,  may  be  shown  by  placing  a  small  tin  dish 
upon  the  top  of  a  gold  leaf  electroscope,  having  in  it  a  red  hot  coal,  just  taken  from  the 
fire      Sprinkle  a  few  drops  of  water  upon  the  coal  and  the  evaporation  will  at,  once  canfe 
the  gold  leaves  to  diverge.     This  will  not  succeed  either  with  charcoal  or  coke.     It  does 
best  with  a  hot  iron  put  into  the  water 

8.  To  show  that  hydrogen,  when  it  burns,  products  electricity,  set  fire  to  a  jet  of  hy- 
drogen, so  as  to  forip  a  flame  about  3  inches  in  length ;  then  place  a  coil  of  platinum 
wire  so  as  to  be  about  4  inches  distant  from  the  external  surface  of  the  flame,  then  let 
the  upper  extremity  of  the  coil  be  bent  so  as  to  touch  the  plate  of  the  electroscope,  and 
signs  of  positive  electricity  will  make  their  appearance. 

9.  To  show  electrical  attraction  and  repulsion,  perform  the  experiments  described  in 
§  304 ;  also,  rub  a  glass  rod  with  a  piece  of  silk,  and  hold  it  near  small  pieces  of  paper, 
these  bits  will  be  first  attracted,  and  then  repelled. 

10.  To  show  that  bodies  similarly  electrified  repel,  and  differently  electrified  attract 
each  other,  electrify  two  pith  balls  by  a  piece  of  excited  glass,  and  on  bringing  them  near 
each  other,  repulsion  will  take  place ;  electrify  one  with  a  glass  rod,  and  the  other  with 
a  stick  of  sealing-wax,  and  bring  them  near  each  other,  and  attraction  will  ensue.     These 
experiments  may  be  multiplied  indefinitely  by  means  of  the  e'ectrical  machine. 

11.  To  show  the  induction  of  electricity,  insulate  a  metallic  conductor  upon  a  glass 
stand,  and  suspend  from  one  extremity  two  pith  balls  by  distinct  threads :  then  bring 
nenr  to  the  opposite  extrem  ty  an  excited  glass  rod,  as  in  F/£.  117.  and  it  will  be  found 
that  the  pith  ball*  will  become  excited  with  positive  electricity,  and  repel  one  another  ; 
remove  the  glass  rod,  and  the  pit.h  balls  will  immediately  return  to  their  natural  state  ; 
bring  it  back  again,  and  the  electrical  excitement  will  be  restored. 

12.  If  the  insulated  conductor  be  touched  by  the  finger  when  excited  by  induction, 
a  spark  will  be  drawn  from  it,  and  the  pith  balls  will  collapse.     By  this  process  the  posi- 
tive electricity  will  be  withdrawn,  and  only  negative  electricity  left  upon  the  conductor, 
with  which  the  pith  balls  will  almost  immediately  become  charged,  and  again  repel  each 
other. 


GALVANIC    ELECTRICITY.  311 

i 
V 

1 3.  Walk  rapidly  over  a  brussels  carpet,  on  a  cold  day  in  vrinter  ;  this  will  charge  the 
Carpet  with  electricity,  and  the  effect  will  be  to  electrify,  by  induction,  all  the  artic.es  in 
the  room  ;  apply  the  hand  to  the  gas  fixtures,  aud  a  spark  will  be  perceived ;  this  spark, 
if  made  to  pass  through  the  current  of  gis  issuing  from  the  burner,  will  be  smncieiit  to 
infl.ime  it.     All  persons  moving  upon  the  carpet  will  become  electrified,  aui  communi- 
cate sparks  to  those  who  enter  tho  room.     These  effects  are  not  prevented  by  the  inter- 
vention of  glass  screens  between  the  excited  electric  and  the  conductor  on  which  the 
electricity  is  induced.     See  Fig.  118. 

1 4.  An  amalgam  for  the  rubbers  of  the  electrical  machine  may  be  made  by  melting  i 
oz.  of  zinc  in  a  ladle,  and  stirring  into  it  2  oz.  of  mercury  ;  when  cold,  pound  it  \vita  a 
little  wax  or  grease,  and  then  spread  it  smoothly  upon  the  leather  with  a  hot  spatula. 

15.  The  electrical  machine,  for  successful  action,  must  have  the  plate  thoroughly 
cleaned,  be  well  dried  and  warmed,  the  rubbers  provided  with  fresh  amalgam,  and  t.ie 
prime  conductor  carefully  cleaned  from  dust ;  a  metallic  conductor  should  also  lead  from 
the  rubbers  to  the  ground. 

1 6.  The  principle  of  the  Leyden  jar  may  be  shown  by  pasting  a  piece  of  tin  foil  upon 
each  side  of  a  pane  of  glass  to  within  an  inch  or  more  of  the  edge ;  fasten  a  thread  hold- 
ing a  pith  ball  to  the  tin  foil  on  each  side,  with  a  piece  of  wax ;  connect  one  coating  with 
the  ground,  and  touch  the  prime  conductor  with  the  other ;  the  plate  of  glass  will  be- 
come charged,  and  the  pich  balls  fly  out  to  some  distance  ;  then  establish  a  connection 
between  the  two  sides  by  a  bent  wire ;  a  shock  wLl  immediately  pass,  and  the  two  balls 
will  fall. 

17.  To  show  the  mechanical  effects  of  electricity,  repeat  the  experiment  indicated  in 
Fig.  129. 

1 8.  To  show  the  heating  effect,  pass  an  electrical  charge  through  two  wires  nearly 
touching  each  other,  in  the  bulb  of  a  large  air  thermometer,  Fig.  45 ;  the  liquid  will 
immediately  rise  in  the  tube. 

1  }.  To  show  the  physiological  effect,  pass  the  shock  from  a  Leyden  jar  through  a  cir- 
cle formed  by  several  persons  joining  hands  ;  the  person  at  one  extremity  should  gra.-p 
the  outside  of  the  bottle  with  moistened  hands,  and  the  one  at  the  other  should  touch 
t'.ie  knob  with  his  moistened  finger.  The  jar,  in  order  to  avoid  the  danger  of  falling, 
should  be  placed  firmly  upon  a  table. 

20.  The  chemical  effects  may  be  shown  by  the  apparatus  indicated  in  Fig.  130  ;  also, 
by  pissing  a  spark  through  a  jet  of  hydrogen  issuing  from  a  small  tube  ;  or,  through  a 
jet  of  common  illuminating  gas;  also,  by  passing  a  succession  of  sparks  over  a  piece  of 
paper  moistened  by  a  mixture  of  a  solution  of  iodide  of  potassium  and  common  starch  ; 
the  iodide  is  decomposed,  i,/dine  is  set  free,  and  a  blue  color  struck  by  combination  with 
the  starch;  also,  by  passing  a  succession  of  sparks  through  gold  or  platinum  wires  i.i- 
serted  in  a  tube  filled  with  water ;  at  each  discharge  bubbles  of  oxygen  and  hydrogen 
will  rise  from  each  wire ;  when  the  tube  is  filled  with  gas  so  as  to  expose  the  wires,  the 
next  shock  will  cause  the  recombination  of  the  gases  with  the  formation  of  a  small 
amount  of  water. 

21.  The  magnetic  effects  may  be  shown  by  twisting  a  fine  platinum  wire  into  »  spiral, 
inserting  a  fine  steel  needle,  wound  with  silk  thread,  in  its  axis,  and  passing  a  succession 
of  electric  shocks  ;  the  needle  will  speedily  become  magnetic. 

For  a  more  complete  list  of  electrical  experiments,  the  student  is  referred  to  a  small 
work  entitled  "  Electrical  Experiments,  by  G.  Francis." 


§  II.    Galvanic  Electricity. 

322.  Galvanic  Electricity.  This  is  the  name  given  to  that 
peculiar  form  of  electricity  which  is  produced  by  chemical  ac- 
tion. It  is  generally  called  after  its  discoverer,  Galvani,  Gal- 
vanic Electricity,  or  Galvanism.  As  distinguished  from  Stati- 
cal Electricity,  it  is  called  Dynamical,  because  it  is  electricity 

322.  Ky  whom  was  gilvanic  electricity  discovered  1     Why  called  voltaic  ?     What  is  the 
difference  between  galvanic  and  statical  electricity  ? 


312  GALVANI'S    THEORY. 

in  action,  prcrlucin^  force,  and  flowing  like  a  current.  It  is  al^o 
sometimes  called  Voltaic  Electricity,  from  Volta,  one  of  its  most 
successful  investigators.  Galvanic  electricity  differs  from  stati- 
cal, in  this  respect,  that  the  latter  is  more  intense  in  its  charac- 
ter and  effects,  producing  more  vivid  sparks,  and  giving  more 
violent  shocks;  while  theformeris  produced  in  a  continuous  and 
steady  flow,  and  apparently  in  larger  quantity.  This  difference 
will  become  more  manifest  as  we  proceed. 

323.  Discovery  of  Galvanism.  The  discovery  of  galvanic 
electricity  was  made  by  Galvani,  the  Professor  of  Anatomy  in 
the  University  of  Bologna,  in  the  year  1790,  and  it  was  not 
known  to  exist  until  some  time  after  the  most  important  princi- 
ples of  statical  electricity,  or  the  electricity  of  the  machine,  had 
been  well  established.  The  discovery  is  said  to  have  been 
made  in  the  following  manner.  It  happened  that  several  frogs 
lay  upon  the  table  of  the  laboratory,  near  to  which  Galvani's 
assistant  was  engaged  in  experimenting  with  an  electrical  ma- 
chine. While  the  machine  was  in  action,  the  assistant  acciden- 
tally touching  one  of  the  frogs  with  the  knife  which  he  held 
in  his  hand,  the  limbs  of  the  frog  became  suddenly  affected 
with  convulsive  movements.  When  the  circumstance  was  re- 
ported to  Galvani,  he  commenced  a  series  of  experiments  for 
the  purpose  of  discovering  the  cause  of  the  strange  phenome- 
non. With  this  view,  he  dissected  several  frogs,  separating  the 
legs,  thighs,  and  lower  part  of  the  spinal  column,  from  the 
remainder,  so  as  to  lay  bare  the  lumbar  nerves.  He  then 
passed  copper  hooks  through  the  flesh  above  the  legs,  and 
suspended  some  of  them  by  these  hooks  from  the  iron  bar  of 
the  balcony  of  his  window,  in  order  to  ascertain  if  they  would 
be  affected  by  the  electricity  of  the  atmosphere,  and  found 
that,  whenever  the  wind,  or  any  other  accidental  cause,  brought 
the  muscles  of  the  leg  into  contact  with  the  iron  bar,  the  limbs 
were  affected  with  convulsive  movements,  similar  to  those  pro- 
duced by  the  sparks  taken  from  the  prime  conductor  of  the 

^X/    electrical  machine. 
/\^     324.   Galvani's  Theory.     Galvani  imagined  that  he   had 

/  ^fcere  discovered  the  cause  of  muscular  contraction  in  living  ani- 
mals, and  ascribed  it  to  the  influence  of  electricity.  He  sup- 
posed that  this  animal  electricity  originates  in  the  brain,  and 
is  distributed  by  the  nerves  to  every  part  of  the  system ;  the 
different  parts  of  each  muscular  fibril,  he  believed,  were  in  oppo- 

I    323.  In  what  manner  did  Galvani  make  the  discovery  ?— 324.  State  his  theory. 


VOLTA'S  THEORY.  313 

site  states  of  electrical  excitement,  like  the  outer  and  inner  sur- 
face of  a  charged  Leyden  jar,  and  that  contractions  of  the  mus- 
cle take  place  whenever  the  electricity  is  allowed  to  pass.  This 
discharge,  he  supposed,  was  made  during  life,  through  the  medi- 
um of  the  nerves,  and  in  his  experiments  by  means  of  the  cop- 
per hooks  and  the  iron.  Thus,  if,  as  represented  in  Fig.  131, 
the  spinal  cord  of  a  frog  were  touched  by  a  zinc  rod,  z,  to  the 

Fig.  131. 


GalvanVs  Experiment. 


opposite  extremity  of  which  is  attached  a  piece  of  copper  c,  and 
the  copper  wire  then  brought  into  contact  with  the  outside  of 
the  frog's  leg,  the  convulsive  movements  which  take  place  he 
supposed  were  owing  to  the  passage  of  the  electricity  from  the 
nerve  to  the  muscle,  through  the  metallic  conductors,  exactly 
as  a  Leyden  jar  is  discharged  by  a  curved  discharging  rod,  as 
shown  in  Fig.  123.  These  views  were  very  generally  adopted, 
and  the  new  agent  passed  under  the  name  of  the  galvanic  fluid, 
.  or  animal  electricity. 

325.  Correction  of  Galvani's  theory  by  Volta.  Volta,  a 
Acelebrated  Italian  philosopher,  and  then  professor  at  Como, 
'  afterwards  at  Pavia,  already  known  by  his  invention  of  the 

325.  Give  Volta's  correction  of  Galvani's  theory. 


314  THE    VOLTAIC    PILE. 

electrophorus,  the  condensing  electrometer,  and  the  eudiometer, 
repeated  the  experiments  of  Galvani,  and  came  to  a  precisely 
opposite  conclusion.  He  found  that  the  convulsive  movements 
of  the  frog  never  took  place  when  the  metallic  connector  was 
formed  of  one  single  metal,  but  only  when  a  compound  con- 
nector was  employed,  composed  of  two  metals,  such  as  zinc  and 
copper,  as  represented  in  Fig.  131.  Hence  he  concluded  that 
the  electricity  was  produced  by  the  contact  of  these  two  dissimi- 
lar metals,  and  that  it  was  the  nerve  and  the  leg  which  consti- 
tuted the  discharger ;  precisely  the  reverse  of  the  opinion  of 
Galvani.  After  a  long  contest,  Volta  finally  established  his 
position,  and  showed  that  when  two  metals  are  made  to  touch 
each  other,  they  become  excited,  the  one  with  positive,  the  other 
with  negative  electricity,  in  all  cases.  Thus,  when  a  piece  of 
silver  is  placed  upon  the  tongue,  and  a  piece  of  zinc  under  it, 
and  then  their  two  edges  are  made  to  touch  each  other,  there 
will  be  a  passage  of  electricity  from  one  to  the  other,  which 
will  be  made  sensible,  not  only  by  a  peculiar  metallic  taste,  but 
also  by  a  slight  flash  of  light  before  the  eyes,  especially  if  these 
Le  closed.  Again,  on  touching  the  knob  of  a  delicate  .condens- 
ing electroscope,  containing  two  slips  of  gold  leaf,  as  in  Fig. 
115,  with  a  piece  of  polished  zinc,  the  leaves  diverge,  and  it 
can  be  shown  that  they  are  electrified  negatively.  This  leads 
to  the  conclusion  that  by  its  contact  with  the  zinc,  the  copper 
knob  of  the  instrument  becomes  charged  with  positive  electri- 
city, while  the  zinc  is  charged  with  negative.  The  quantity  of 
electricity  evolved  by  two  pieces  of  metal  being  very  small, 
Yolta  tried  the  experiment  of  uniting  many  pieces  in  one 
series,  and  arranging  them  in  pairs,  with  a  conductor  between 
them,  and  found  that  the  electrical  influence  was  increased  in 
proportion  to  the  number  of  plates  thus  combined. 

32£.  The  Voltaic  Pile.  These  experiments  finally  led  to 
the  construction  of  the  Voltaic  Pile,  the  wonderful  apparatus 
Avhich,  under  the  name  of  the  Galvanic  Battery,  has  immortal- 
ized his  name,  and  conferred  lasting  benefits  upon  man.  The 
Voltaic  Pile  consists  of  several  pairs  of  zinc  and  copper  plates, 
placed  one  upon  the  other,  with  discs  of  thick  fibrous  paper, 
moistened  with  a  solution  of  sulphate  of  soda,  placed  between 
each  pair,  and  the  pair  immediately  above  it.  Thus,  first  we  have 
copper,  then  zinc,  then  paper ;  after  that,  copper,  zinc,  paper,  again. 


Give  illustrations  of  the  production  of  electricity  by  the  contact  of  two  metals. — 326. 
Describe  the  yoltr.ic  pile.  How  may  siiocks  be  taken  from  this  pile  ?  iiow  may  several 
piles  l/e  connected  ? 


THE    TRUE    THEORY    OF 


315 


It  is  quite  evident  that  this  order  being 
strictly  observed,  while  a  zinc  disc  termi- 
nates the  upper  end  of  the  pile,  a  copper 
disc  will  terminate  the  lower  end.  A 
wire  being  then  attached  to  the  extreme 
plate  at  each  end,  and  the  opposite  ex- 
tremities being  brought  together,  a  flow 
of  electricity  takes  place,  which  makes 
itself  manifest  by  a  faint  spark  when  the 
wires  are  separated,  and  also  when  they  are 
again  united.  The  power  of  this  pile  in- 
creases with  the  number  of  pairs  of  plates 
employed.  A  pile  composed  of  two  doz- 
en plates  of  each  metal  will  give  a  slight 
shock,  which,  when  taken  by  the  hands, 
may  be  felt  up  to  the  elbows.  The  mode 
of  receiving  the  shock  is  to  wet  the  hands, 
and  then  placing  one  of  them  in  contact 
with  the  zinc  plate  which  terminates  one 
end  of  the  pile,  to  touch  with  the  other 
hand  the  copper  plate  which  terminates 
the  other  end ;  or,  these  two  plates  may 
be  touched  with  wires  wound  with  wet 
rags,  and  held  one  in  each  hand.  When 
the  galvanic  current  is  to  be  passed 
through  any  substance,  this  is  done  by 
connecting  a  wire  with  each  terminating 
plate ;  the  two  wires  are  then  brought 
near  each  other,  and  the  substance  being 

placed  between  them,  the  fluid  passes  from  one  wire  to  the  other, 
and  so  through  the  substance  in  question.  Any  number  of  these 
piles  may  be  connected  together  by  making  a  metallic  communi- 
cation between  the  last  plate  of  the  one,  and  the  first  plate  of 
the  other,  always  taking  care  to  connect  the  copper  end  of  each 
pile  with  the  zinc  end  of  the  preceding  pile.  In  this  manner, 
a  galvanic  battery  may  be  constructed,  the  power  of  which  will 
be  proportionate  to  the  number  of  plates  employed. 

327.  True  theory  of  the  Pile.  Volta  was  of  the  opinion 
that  the  mere  contact  of  the  two  dissimilar  metals,  zinc  and  cop- 
per, generated  the  electricity,  and  that  the  moistened  discs  only 
served  as  conductors  to  convey  the  electricity  generated  by  one 


The  Voltaic  Pile. 


327.  What  is  the  true  theory  of  the  pile? 


SI 6  THE   PILE    IS    CHEMICAL    ACTION. 

pair  to  the  lower  plate  of  the  pair  immediately  next  it ;  and  so 
on  through  the  whole  apparatus.  It  has  since,  however,  been 
conclusively  shown  that  the  sole  cause  of  the  electrical  current 
is  the  chemical  decomposition  of  the  saline  solution  by  the  zinc 
plates  employed.  In  all  cases  of  galvanic  action,  there  must  be 
a  liquid  composed  of  at  least  two  chemical  elements,  susceptible 
of  decomposition  .by  one  of  the  metals,  and  not  by  the  other ; 
the  latter  metal  acting  only  the  part  of  an  electrical  conductor. 
338.  Chemical  constitution  of  the  substances  used  to  pro- 
duce Voltaic  Electricity.  Simple  chemical  action  of  one  sim- 
ple substance  upon  another,  such  as  bromine  upon  iron,  is  not 
sufficient  to  excite  galvanic  electricity.  It  must  be  such  chemi- 
cal action  as  to  produce  the  separation  of  the  elements  united  in 
some  compound  substance.  This  separation  can  be  effected  by 
introducing  some  third  simple  substance,  which  has  a  stronger 
affinity  for  one  of  the  elements  in  the  compound  than  this  has  for 
the  other.  In  all  such  cases  the  new  element  introduced  goes 
to  the  formation  of  a  new  compound  substance,  by  uniting  with 
one  of  the  original  elements,  and  the  other  element,  existing  in 
the  orig'nal  compound,  is  set  free.  It  is  also  essential  that  the 
compound  to  be  decomposed  should  be  in  the  liquid  state,  and 
the  new  element,  introduced  for  the  purpose  of  decomposing  it, 
must  be  a  solid.  A  second  plate,  consisting  of  a  good  conductor 
of  electricity,  must  also  be  provided.  The  word,  element,  is 
here  used  in  its  strict  chemical  sense,  as  explained  in  §  30.  It 
would  appear  that  as  the  molecular  disturbance  created  by  fric- 
tion is  sufficient  to  produce  the  manifestation  of  statical  electri- 
city, so  the  molecular  disturbance  produced  by  violently  rending 
one  chemical  element  from  another,  by  means  of  the  chemical 
affinity  exerted  by  a  third  element,  is  sufficient  to  produce  the 
manifestation  of  galvanic  electricity.  The  compound  liquid 
which  is  generally  used  in  practice,  is  common  wa.er,  slightly 
acidulated  with  sulphuric  acid,  and  the  third  element  employed 
is  metallic  zinc ;  for  the  conductor,  the  metals  copper  and  pla- 
tinum are  often  employed,  and  sometimes  common  charcoal. 
Water  is  composed  of  the  two  elements,  hydrogen  and  oxygen  ; 
the  oxygen  is  violently  separated  from  the  hydrogen  by  the  zinc 
under  the  influence  of  affinity  ;  an  oxide  of  zinc  is  formed  on  the 
one  hand,  and  hydrogen  is  set  free  upon  the  other,  and  at  the 

828.  Ts  the  simple  chemical  action  of  one  substance  upon  another  sufficient  to  produce 
galvanic  electricity  ?  What  sort  of  chemical  action  must  it  be  ?  In  what  state  must  the 
compound  substance  to  be  decomposed  be?  Is  molecular  disturbance  really  the  cause 
of  galvanic  electricity  ?  What  is  the  compound  liquid  generally  used  ?  What  is  the  de- 
composing metal  employed  ? 


PROOF    THAT    CHEMICAL    ACTION"  317 

same  time  a  certain  amount  of  electricity  is  evolved.  In  all 
tho.-e  instances  in  which  the  simple  contact  only  of  different 
metals,  without  the  employment  of  any  liquid  agent,  has  been 
found  to  produce  electricity,  it  is  always  the  case  that  the  mois- 
ture of  the  air  is  really  decomposed  by  the  most  oxidisable  of 
the  metals,  while  the  electricity  set  free,  is  carried  off  by  the 
0:her. 

329.  Proof  that  Chemical  Decomposition  is  the  source  of 
Galvanic  Electricity.  That  chemical  decomposition  is  the 
souive  of  the  electricity  of  the  voltaic  pile  is  well  shown  by 
what  is  called  a  simple  galvanic  circuit.  Let  a  glass  cup  be 
provided,  Fig.  133,  fill  it  about  two-thirds  with  a  mixture  of  8 
parts  by  volume  of  water  to  1  of  sulphuric 
ac^d ;  then  immerse  in  it  a  piece  of  brightly 
polished  zinc,  6  inches  in  length,  and  as  wide 
aS  ^6  CUP  W^  admit-  On  immersing  the 
zmc  m  tne  acidulated  water,  bubbles  of  hy- 
drogen are  at  once  abundantly  discharged 
upon  its  surface,  set  free  by  the  abstraction 
of'  oxygen  from  the  water  by  the  zinc,  and 
these  bubbles  rising  through  the  liquid,  at 
length  escape  into  the  air.  Now  place  in  the 
same  vessel  a  slip  of  polished  copper,  and  so 

No  coiinfr.'iDit  Leliueen        -,  .,    ,  1,1          •  i 

the  Rates.  long  as  it  does  not  touch  the  zinc,  no  change 

will  be  observed,  and  the  bubbles  of  hydro- 
gen will  continue  to  escape  as  before,  at  the  surface  of  the  zinc 
plate.     The  instant,  however,  that  any  me- 
Fig.  134.  tallic  communication  is  made  between  the 

two  plates,  as  in  Fig.  134,  where  the  two 
plates  have  been  inclined  so  that  the  upper 
edge  of  the  copper  plate  has  been  brought 
into  contact  with  the  zinc,  it  will  be  observed 
that  the  bubbles  of  hydrogen  are  no  longer 
discharged  upon  the  zinc,  but  upon  the  cop- 
per. There  is  no  visible  transfer  through 
the  liquid,  but  the  faej  is  certain,  and  it  is 
quite  evident  that  an  influence  of  some  sort 
has  been  set  in  motion,  by  which  the  point 
of  discharge  for  the  gas  has  been  trans- 
ferred to  the  copper,  and  a  current  produced,  indicated  in  the 

329.  Prove  that  chemical  decomposition  is  the  source  of  galvanic  electricity.  Describe 
Fis-  133-  -F'V-  134.  What  is  the  effwt  of  amalgamating  the  zinc  plates?  What  other 
effects  can  be  produced  by  the  wires  besides  the  evolution  of  gas  ? 


318  IS  THE  CAUSE  OP  THE  CURRENT. 

figure  by  the  direction  of  the  arrow.     Separate  the  two  metals, 
and  the  gas  ceases  to  be  discharged  upon  the  copper,  and  rises 
again  from  the  zinc.    If,  instead  of  bringing  the  plates  themselves 
into  contact,  the  connection  be  made  by  wires,  or  any  other 
good  electrical  conductor,  the  result  will  be  the  same  ;  Fig.  135. 
If   the    zinc,    after    being    thoroughly 
Fig.  135.  cleansed  by  immersion  in  the  acidula- 

— •>  \  ted  water,  be  rubbed  with  mercury,  it 
^^)  immediately  acquires  a  bright  amalga- 
mated surface,  and  when  restored  to  the 
water,  it  no  longer  exerts  any  decompos- 
ing action,  and  particles  of  hydrogen 
are  no  longer  seen  to  rise  from  it. 
The  instant,  however,  that  a  connection 
is  made  by  a  wire,  or  otherwise,  with 
the  conducting  plate,  hydrogen  bubbles 
at  once  begin  to  be  discharged  from  it 

The  Plates  connected  by  a  Wire.       &S    before.        The    Cause    of    this    IS    IK)t 

understood,  but  constant  use  is   made 

of  the  fact  to  protect  the  zinc  plates  from  corrosion,  except  dur- 
ing the  period  when  the  battery  is  actually  in  action.  The  evo- 
lution of  gas  is  not  the  only  effect  observed ;  the  wires,  if  sepa- 
rated, will  emit  a  spark  of  electricity.  If  they  are  wound  around 
the  bulb  of  a  delicate  air  thermometer,  (Fig.  45,)  the  liquid  will 
rise  in  the  tube,  indicating  the  production  of  heat ;  if  they  are 
wound  about  a  piece  of  soft  iron,  the  iron  will  become  magnetic, 
and  attract  iron  filings ;  if  one  wire  be  applied  to  the  crural 
nerve  of  a  frog,  and  the  other  to  the  outside  of  the  muscle,  the 
leg  will  be  violently  convulsed;  if  dipped  into  acidulated  water, 
it  will  be  decomposed,  oxygen  will  appear  at  one  pole,  and  hy- 
drogen at  the  other.  In  short,  the  wires  will  emit  sparks,  pro- 
duce heat  and  magnetism,  give  shocks,  effect  chemical  decompo- 
sition, and  indicate  the  passage  of  a  continuous  current  of  gal- 
vanic electricity. 

330.  The  decomposing1  plate  is  the  point  of  departure  of  the 
electrical  current.  -4t  the  same  time  that  hydrogen  is  dis- 
charged upon  the  copper  plate,  a  corresponding  portion  of  ox'de 
of  zinc  is  formed  on  the  zinc  plate  by  the  affinity  of  the  zinc 
for  the  oxygen  of  the  water,  and  this  oxide  is  eventually  united 
with  the  sulphuric  acid,  converted  into  sulphate  of  zinc,  and 
finally  dissolved  in  the  remaining  water.  If  it  were  not  for  the 

830.  What  is  the  point  of  departure  of  the  electrical  current? 


MODE    OF    TRANSFER 


319 


sulphuric  acid,  the  oxide  of  zinc  which  is  formed,  being  an  in- 
soluble substance,  would  speedily  cover  the  zinc  plate  with  a 
thick  deposit,  and  put  a  stop  to  its  decomposing  .action  upon  the 
water.  By  the  introduction  of  the  sulphuric  acid,  the  oxide  is 
removed  as  fast  as  formed,  and  converted  into  the  soluble  sul- 
phate of  zinc,  which  is  at  once  dissolved  in  the  water.  Thus 
.the  zinc  plate  is  kept  bright,  and  its  decomposing  action  is  sus- 
tained until  the  water  has  dissolved  all  the  sulphate  of  zinc  of 
which  it  is  capable.  As  soon  as  this  point  is  reached,  the  oxide 
of  zinc  begins  again  to  coat  the  zinc  plate,  and  to  diffuse  itself 
in  a  cloudy  precipitate  through  the  water,  thereby  hindering 
the  ready  transference  of  the  molecules  of  gas,  and  obstructing 
the  pa^sacre  of  the  electric  current.  By  the  combined  opera- 
tion of  both  these  causes,  the  process  is  brought  to  a  conclusion. 
If  some  other  chemical  compound  be  employed,  instead  of  water, 
which  is  capable  of  decomposition  by  the  copper,  and  not  by 
the  zinc,  the  electrical  current  will  be  reversed,  and  will  set  out 
from  the  copper  towards  the  zinc.  In  all  cases,  it  is  the  metal 
which  exerts  the  decomposing  action  by  which  the  current  is 
set  in  motion,  and  from  which  it  starts, 

331.  Mode  of  transfer  of  the  Hydrogen  The  mode  in 
which  the  hydrogen  is  made  to  appear  upon  the  copper  plate  is 
believed  to  be  as  follows.  Oxygen  is  thought  to  be  naturally 

charged  with  negative,  and  hydro- 
Fig-  13G.  geu  with  positive,  electricity ;  con- 
sequently, as  oppositely  electrified 
bodies  attract  each  other,  when 
brought  into  close  contact,  these  two 
substances  unite  under  the  influ- 
ence of  this  electrical  attraction, 
and  form  water.  Every  particle 
of  water  consists,  then,  of  two  ele- 
ments, and  a  row  of  them  extend- 
ing from  the  zinc  to  the  copper 
plate,  may  be  represented,  as  in 
Fig.  136.  If  now  we  suppose  the 
i^Pp  oxygen  of  the  particle  of  water, 
next  the  zinc,  to  quit  the  hydrogen 

Mod*  of  Transfer  of  Hydrogen,       with  which   it   is   united,  and   to 

connect   itself  with    the    zinc,  as 
represented  in  the  figure,  and  that  a  certain  amount  of  electricity 

What  is  the  use  of  the  sulphuric  acid?    How  is  the  process  brought  to  a  conclusion? 
—331    How  is  the  hydrogen  made  to  appear  upon  the  copper  plate? 


320  OF    THE    HYDROGEN. 

1 

is  excited  by  the  transfer,  which  concentrates  itself  upon  the 
deserted  particle  of  hydrogen,  then  this  particle  of  hydrogen, 
in  consequence  of  the  good  conducting  power  of  the  copper,  will 
be  attracted  towards  it ;  but  corning  into  contact  with  the  parti- 
cle of  water  next  it,  by  its  superior  electrical  excitement  it  ap- 
propriates its  oxygen  to  itself,  forming  a  new  particle  of  water, 
and  then  communicates  its  electricity  to  the  second  particle  of 
hydrogen  thus  set  -free.  This  second  particle  of  hydrogen  is  in 
turn  started  towards  the  copper  plate,  but  in  its  way  meeting 
with  the  next  particle  of  water,  it  seizes  upon  its  oxygen  in  the 
manner  represented  in  the  figure ;  and  so  the  process  goes  on, 
every  particle  of  hydrogen  set  free,  decomposing  the  particle  of 
water  next  it  in  the  shortest  line  of  direction  to  the  copper 
plate,  until  finally  the  last  particle  of  water  immediately  touch- 
ing the  copper  plate  is  decomposed,  and  its  hydrogen  having 
nothing  to  unite  with,  is  discharged,  together  with  the  accumu- 
lated electricity,  upon  the  copper  plate,  and  escapes.  The  elec- 
tricity thus  produced  finds  its  way  back  through  the  copper  and 
the  connecting  wire,  to  the  zinc,  and  thus  returns  to  the  point 
from  which  it  set  out.  In  this  manner  there  is  a  continual  pre- 
cipitation of  particles  of  hydrogen  upon  the  copper,  and  a  steady 
current  of  electricity  kept  in  motion,  until  the  effect  of  the  zinc 
upon  the  liquid  ceases,  and  no  more  water  is  decomposed.  In 
all  cases,  it  will  be  seen  that  the  current  is  from  the  zinc  to  the 
copper.  There  is  good  reason  for  doubting  whether  the  theory 
described  above,  of  the  opposite  electrical  state  of  the  oxygen 
and  hydrogen  is  strictly  true  ;  but  there  is  no  doubt  of  the  trans- 
fer of  the  hydrogen,  and  that  it  is  probably  effected  in  the  man- 
ner indicated. 

332.  The  part  played  by  the  Copper.  It  is  evident  that  it 
is  the  zinc  which  is  the  generating  plate,  and  that  the  copper 
'acts  simply  as  an  electrical  conductor.  Consequently,  any  good 
conductor  of  electricity  will  answer  equally  well,  provided  only, 
in  all  cases,  it  be  not  one  which  itself  acts  upon  the  acidulated 
water,  because,  in  this  case,  an  opposite  current  would  be  set  in 
motion,  which  would  neutralize  the  first.  The  conductor  need 
not  necessarily  be  metallic.  Charcoal  is  employed  in  many  of 
the  best  batteries,  and  in  others,  slips  of  platinum.  In  all  case?, 
the  conducting  plate  is  charged  with  positive  electricity,  and  the 

Describe  the  process  of  circulation  which  takes  place.— 332.  What  is  the  part  played 
by  the  copper?  Must  the  conducting  plate  be  made  of  metal?  What  is  the  elcc  rical 
condition  of  the  two  plates  ?  What  is  meant  by  a  negative  electric  ?  By  a  positive 
electric? 


THE    POLARIZATION" 


321 


Positive  and  Negative  Plates. 


generating  plate  with  negative.  In 
Fig.  137,  the  two  pla  es  are  distin- 
guished simply  by  the  signs  -j- 
and  — .  The  ends  of  the  two  wires, 
connected  respectively  with  the  two 
plates,  are  called  positive  and  nega- 
tive poles,  or  sometimes  positive  and 
negative  electrodes.  Every  chemi- 
cal element  which  appears  at  the 
positive  pole  is  called  a  negative  elec- 
tric, and  every  one  appearing  at  the 
negative  pole  a  positive  electric. 
This  is  in  accordance  with  the  theory 
of  electricity  previously  explained, 
that  a  body  positively  electrified  will  attract  negative  electrics, 
and  a  body  negatively  electrified  positive  electrics:  §  306. 

333.  The  polarization  and  transfer  of  the  elements  of  the 
Liquid,  and  the  polarization  of  the  Solid  particles  of  the  circuit 
necessary  for  the  electrical  force  to  circulate.  The  transference 
of  the  particles  of  hydrogen,  arid  the  production  of  the  electrical 
force,  as  just  described,  is  supposed  to  be  preceded  by  the  polar- 
ization of  the  entire  circuit,  both  solid  and  liquid.  By  po'ariza- 
tion  is  meant, — as  has  been  previously  explained  in  describing 
the  discharge  of  the  Leyden  jar,  §  316, — the  disturbance  of  the 
natural  equilibrium  of  the  electricity  .residing  in  the  molecules 
of  a  substance,  and  its  distribution  at  the  opposite  poles  of  each 
molecule.  Thus  in  Fig.  138,  the  upper  row  represents  a  series 

of  particles  of  water,  each  corn- 


Fig.  138. 
Unpolarized   Particles  of  Water. 


-Ao  -Ao  - Ao  - 


posed  of  oxygen  and  hydrogen, 
in  an  unpolarized  state;  the 
second  row  represents  the  same 
particles  of  water  in  a  polarized 
state,  in  which  the  particles 
have  been  turned  around,  and 
the  negative  oxygen  made  to 
alternate  with  the  positive  hy- 
drogen. This  polar  state  is 
produced  by  bringing  a  highly  charged  positive  electric  into 
proximity  with  the  negative  oxygen,  on  the  right  of  the  figure. 
The  oxygen  is  at  once  attracted,  the  hydrogen  repelled  and  at 
the  same  time  its  positive  electricity  greatly  intensified  by  in- 


H  o  AH  o  AH  o  A»  OAH  oAw  o> 


Polarized  Particles  of  Water. 


333    What  is  meant  by  the  polarization  of  the  liquid,  as  well  as  solid,  part  of  the  cir- 
cuit ?     What  is  polarization?    Describe  Fig.  138. 


322 


OF    THE    ENTIRE    CIRCUIT. 


Fig.  139. 


duction ;  a  similar  change  takes  place  in  all  the  molecules,  and 
the  polariza  ion  is  propagated  throughout  the  series.  Jn  the 
case  of  the  simple  galvanic  circuit,  the  polarization  is  supposed 
to  be  produced  in  the  following  manner :  when  the  plate  of  zinc 
is  introduced  into  the  acidulated  water,  the  part  which  touches 
the  liquid,  in  consequence  of  the  chemical  action  which  takes 
place  between  it  and  the  oxygen  of  the  water,  immediately 
becomes  highly  charged  with  positive  electricity,  while  the 
opposite  extremity,  which  is  outside  the  cup,  becomes  negative ; 
this  immediately  polarizes  the  molecules  of  water,  in  the  man- 
ner shown  in  Fig.  138.  As  soon  as  the  copper  plate  is  intro- 
duced, its  molecules  also  become  polarized,  and  the  whole  series 
extending  to  the  extremity  of  the  wire  connected  with  that 
plate,  is  thrown  into  a  similar  state.  The  same  process  also 
takes  place  in  the  zinc  plate,  and  is  propagated  to  the  extreme 
end  of  the  wire  connected  with  it,  as  shown  in  Fig.  139.  As 

the  ends  of  the  wires,  however, 
do  not  touch  each  other,  there  can 
be  no  discharge  ;  there  is  a  state 
of  polar  tension  produced,  extend- 
ing through  the  circuit,  but  no 
discharge,  and  no  current  or  mani- 
festation of  electricity.  Every 
thing,  however,  is  ready  for  the 
discharge,  and  the  instant  the 
metallic  connection  is  completed, 
it  takes  place.  The  first  move- 
ment occurs  on  the  right,  at  the 
lower  part  of  the  zinc  plate.  The 
first  particle  of  oxygen  is  drawn 
off  by  the  zinc,  and  its  negative 
electricity  seizes  hold  of  the  posi- 
tive electricity  of  the  polarized 
particle  of  zinc  next  it,  the  negative  electricity  of  this  particle 
of  zinc  seizes  upon  the  positive  electricity  of  the  polarized 
particle  immediately  adjoining,  and  thus  the  transfer  of  negative 
electricity  proceeds  from  particle  to  particle  up  the  whole  length 
of  the  zinc  plate,  and  through  the  wire  connected  with  it.  On 
the  opposite  side,  at  the  foot  of  the  copper  plate,  the  reverse 
process  is  going  on  ;  the  hydrogen  of  the  last  particle  of  water 
is  released  from  its  oxygen  and  escapes  into  the  air ;  its  positive 


Polarization,  but  no  Discharge. 


State  what  takes  place  as  soon  as  the  zinc  plute  touches  the  acidulated  water.     Is  there 
any  discharge  so  long  as  the  poles  remain  disconnected?    Trace  the  process. 


PROOF    OF    ELECTRIC    TENSION 


323 


electricity  seizes  hold  of  the  negative  electricity  of  the  polarized 
particle  of  copper  nearest  it,  and  sets  free  its  positive  electricity ; 
this  seizes  upon  the  negative  electricity  of  the  next  polarized 
particle ;  the  positive  electricity  thus  set  free  seizes  hold  of  the 
negative  electricity  of  the  particle  next  adjoining,  and  thus  the 
transfer  of  positive  electricity  proceeds  from  particle  to  particle 
up  the  entire  length  of  the  copper  plate,  and  through  the  wire 
connected  with  it.  Consequently,  there  is  a  steady  discharge  of 
positive  electricity  from  the  wire  connected  with  the  copper  plate, 
and  of  negative  electricity  from  the  wire  connected  with  the 
zinc  plate,  and  when  the  two  wires  are  connected,  these  mutu- 
ally attract  each  other,  remain  united  for  a  moment,  and  then 
separate,  and  pass  on  in  opposite  dire2tions.  Thus,  as  Foon  as 
the  metallic  connection  is  completed  between  the  plates,  the 
polar  tension  previously  existing  immediately  springs  into  ac- 
tion, and  a  continued  double  circulation  of  electricity,  in  opposite 
directions,  from  molecule  to  molecule,  is  set  up  through  the 
whole  circuit,  solid,  as  well  as  liquid;  Fig.  140.  In  order  to 

prevent  confusion,  however,  when- 
ever the  direction  of  the  electrical 
current,  is  referred  to,  the  direction 
of  the  positive  current  is  alone 
mentioned. 

334.  Proof  that  a  state  of 
electrical  tension  exists  in  tho 
plates  before  the  actual  passage 
of  the  current.  That  this  state 
of  polar  tension,,  actually  is  pro- 
duced as  soon  as  the  zinc  genera- 
ting plate  and  the  copper  or  pla- 
tinum conducting  plate  are  intro- 
duced into  the  acidulated  water, 
may  be  shown  by  the  following 
experiment,  A  plate  of  zinc,z,  Fiy. 
141,  and  another  of  platinum,  P, 
are  immersed  in  acidulated  water, 

and  the  wire  proceeding  from  each  is  insulated  and  connected 
with  the  two  gilt  disks,  a  and  b,  of  the  electroscope,  E  ;  the^e 
disks  are  insulated  by  the  glass  of  the  apparatus ;  they  slide 
easily  to  and  fro  in  sockets,  and  can  be  brought  within  a  quarter 
of  an  inch  of  each  other ;  a  sing!e  gold  leaf  connected  with  the 


Polarization  and  Discharge, 


What  takes  place  when  the  connection  is  made?     Show  that  a  doub'e  current  circu- 
lates.— 334.  Prove  that  a,  state  cf  electrical  tension  exists  before  the  passage  of  the  current. 


324 


BEFORE    THE    PASSAGE    OF    THE    CURRENT. 


Electric  Tension  before  the  passage  of  the  Current. 


14L  plate   of  the   instru- 

ment is  suspended  be- 
tween them.  Now, 
if  the  positive  end  of 
a  De  Luc's  dry  pile,  D, 
— an  instrument  to  be 
presently  described,  § 
349, — be  brought 
near  the  plate,  this 
will  become  negative 
by  induction,  and  the 
gold  leaf  positive,  as 
indicated  in  the  fig- 
ure. Under  these  cir- 
cumstances, however, 
if  there  were  no  electrical  tension  existing  in  either  a  or  b,  there 
would  be  no  attraction  of  the  gold  leaf  toward  either,  and  it 
would  continue  unmoved ;  but  if  there  be  an  opposite  state  of 
electric  tension  in  the  two  disks,  it  will  be  drawn  towards  that 
which  is  charged  with  negative,  and  repelled  from  that 
charged  with  positive  electricity.  On  examination,  it  is  found 
to  be  attracted  towards  the  disk,  a;  and  the  conclusion,  there- 
fore, is  irresistible,  that  the  zinc  plate  is  in  a  state  of  negative 
electric  tension.  If  now,  the  negative  end  of  the  De  Luc's  pile 
be  presented  to  the  plate  of  the  instrument,  this  will  become 
charged  with  positive  electricity  by  induction,  and  the  slip  of 
gold  leaf  with  negative  electricity.  In  this  state  of  things  the 
gold  leaf  is  attracted  towards  the  disk,  b,  a  conclusive  proof  that 
the  plate,  P,  is  in  a  state  of  positive  electric  tension,  and  this  at 
a  time  when  there  is  no  direct  connection  between  it  and  the 
plate,  z.  It  is  evident,  therefore,  that  a  state  of  electric  tension 
is  produced  the  instant  the  plates  are  introduced  into  the  acidu- 
lated water,  before  the  metallic  circuit  is  completed. 

335.  The  energy  of  the  current  proportionate  to  the  chem- 
ical activity.  If  a  metal  be  employed,  in  place  of  the  zinc, 
which  has  a  more  powerful  affinity  for  oxygen,  and  which  will 
decompose  water  with  greater  energy  and  promptness,  the  inten- 
sity of  the  electrical  current  will  be  greatly  increased.  And  as 
potassium — the  metallic  basis  of  common  potash, — has  a  stronger 
affinity  for  oxygen  than  any  other  metal,  this  would  form  theo- 
retically, the  best  generating  plate  for  a  galvanic  current ;  there 


To  what  is  the  energy  of  the  current  proportioned  ?    What  metal  is  the  best  gene- 


METALLIC    CONNECTION"  325 

arG,  however,  insuperable  objections  to  its  use,  arising  from  the 
intensity  of  its  action, — its  softness  and  want  of  durability,  and 
its  high  cost.  The  experiment,  however,  admits  of  trial,  by 
forming  an  amalgam  of  potassium  with  mercury,  for  it  has  been 
ascertained  that  the  galvanic  relations  of  all  amalgams  are  those 
of  the  most  oxidizable  metal  which  they  contain.  On  the  other 
hand,  the  conducting  plate  must  be  composed  of  some  metal 
exerting  as  little  chemical  action  upon  the  water,  and  having  as 
little  affinity  for  oxygen,  as  possible.  On  this  account,  copper, 
and  still  more,  platinum,  are  admirably  fitted  for  this  purpose. 
The  reason  for  this  necessity  is,  that  in  proportion  to  the  affinity 
of  the  second,  or  the  conducting  plate  for  oxygen,  does  it  tend 
to  produce  a  counter  current  of  electricity  which  neutralizes 
the  primary  current  proceeding  from  the  zinc,  and  proportion- 
ably  reduces  the  energy  of  the  circuit.  Thus,  in  Fig.  1 40,  if  the 
copper  plafe  had  an  affinity  for  oxygen  equal  to  that  of  the 
zinc,  it  would  tend  to  decompose  the  water,  and  set  in  motion  a 
succession  of  particles  of  hydrogen,  charged  with  positive  elec- 
tricity, towards  the  zinc ;  the  result  would  be,  that  two  opposing 
states  of  polar  tension  would  be  produced,  and  at  the  point  of 
meeting,  a  particle  of  hydrogen  on  the  one  side,  would  be  found 
arranged  opposite  to  a  particle  of  hydrogen  on  the  other,  and 
positive  electricity  against  positive  electricity,  repelling  each 
other  with  equal  strength,  and  entirely  preventing  the  passage 
of  any  current.  In  proportion  as  the  conducting  plate  possesses 
an  affinity  for  oxygen,  does  it  tend  to  produce  this  result,  and 
to  stop  the  flow  of  the  current.  For  this  reason,  it  is  necessary 
that  the  conducting  plate  should  have  the  least  possible  affinity 
for  oxygen,  and  be  made  of  platinum,  copper,  gold  or  silveiv  all 
of  which  have  a  feeble  affinity  for  this  substance  ;  and  that  the 
generating  plate,  on  the  other  hand,  should  possess  the  greatest 
possible  affinity  for  the  same  element, 

335.  The  direction  of  the  current  is  dependent  upon  the 
direction  of  the  chemical  action.  In  all  these  cases  the  positive 
electricity  sets  out  from  the  more  oxidizable  metal  which  con- 
stitutes the  generating  plate,  and  traverses  the  liquid  towards 
the  less  oxidizable  metal  which  forms  the  conducting  p!ate. 
The  negative  current,  on  the  other  hand,  starts  from  the  gene- 
rating plate,  and  turns  its  course  in  the  opposite  direction,  i.  e., 
parses  up  the  plate,  instead  of  through  the  liquid.  Consequently, 

What,  metal  would,  in  theory,  make  the  best  generating  plate?  Why  must  the  con- 
ducting plate  be  formed  of  some  metal  which  exerts  110  decomposing  action  on  water? — 
836.  What  is  the  direction  of  the  current? 


326  BETWEEN    THE    PLATES    NOT    NECESSARY. 

there  is  a  current  of  positive  electricity  passing  from  the  wire 
connected  with  the  conducting,  or  copper  plate,  and  of  negative 
electricity  passing  from  the  generating,  or  zinc  plate. 

337-  Direct  metallic  connection  between  the  generating 
and  conducting-  plate  not  necessary.  That  direct  metallic  con- 
tact between  the  two  plates  is  not  necessary  for  the  production  of 
the  current,  may  be  shown  by  the  apparatus  represented  in 
Fig.  142.  Let  z  be  a  zinc  plate,  and  r  a  platinum  plate,  hav- 
ing a  platinum  wire  attached  to  it,  and 
Fig.  142.  kent  so  as  to  touch  a  piece  of  paper,  a, 

moistened  with  a  solution  of  starch  and 
iodide  of  potassium,  and  immersed  in 
water,  strongly  acidulated ;  in  this  case,  it 
will  be  observed,  there  is  no  direct  metal- 
lic connection  between  the  two  plates. 
Iodide  of  potassium  is  a  substance  com- 
posed of  iodine  and  potassium ;  the  starch 
is  a  test  for  iod'rie,  and  is  turned  blue  the 
instant  any  of  the  iodine  is  detached  from, 
the  potassium ;  and  as  the  electric  current 

Contact  not  necessary.          jm3    faQ  pQwer  of  detaching    the  iodine,  if 

there  be  any  electrical  current  transmitted  from  the  platinum 
to  the  zinc  plate,  it  will  be  at  once  manifested  by  the  formation 
of  a  small  blue  spot  at  the  point  where  the  platinum  wire  touches 
the  paper.  Hence  we  conclude  that  the  direct  metallic  connec- 
tion of  the  two  plates  is  not  necessary  for  the  passage  of  the 
current,  but  that  any  good  non-metallic  conductor  of  electricity 
will  answer  equally  well.  This  experiment  also  shows  very 
satisfactorily  that  the  contact  of  two  dissimilar  metals  is  not  the 
cause  of  the  galvanic  current,  and  that  the  hypothesis  suggested 
by  Volta,  in  regard  to  the  theory  of  the  Voltaic  pile  is  not 
strictly  correct. 

338.  Effect  of  the  discharge  of  hydrogen  on  the  conducting 
plate.  It  will  be  observed  in  all  the  cases  heretofore  described, 
that  as  long  as  the  circulation  of  the  electrical  current  continues, 
there  is  a  constant  discharge  of  particles  of  hydrogen  gas  upon 
the  conducting  plate,  whether  it  be  made  of  platinum,  or  cop- 
per. The  bubbles  of  hydrogen  are  discharged  upon  the  sur- 
face of  the  plate  at  every  point  beneath  the  level  of  the  water, 
and  gradually  stream  upwards  towards  the  air.  In  this  way 
most  of  them  escape,  but  a  portion  are  detained  by  the  strong 

337,  Show  that  direct  metallic  connection  between  the  plates  is  unnecessary. — 338. 
What  is  the  effect  of  tiie  dLseliarge  of  hydrogen  ou  the  conducting  plate? 


THE    PLATINUM    PLATE    COATED    WITH    HYDROGEN.     327 


Fi<r.   143. 


attraction  of  adhesion  which  is  exercised  upon  this  gas  by  plati- 
num, and  to  such  a  degree  that  the  plate  will  really  be  covered 
with  a  thin  film  of  gaseous  particles,  too  small  to  be  discovered 
by  the  eye,  but  capable  of  detection  by  other  means,  even  after 
it  has  been  removed  from  the  liquid.  In  this  manner  platinum 
plates  may  be  coated  with  hydrogen.  Now  hydrogen  has  a 
very  strong  affinity  for  oxygen,  and  tends,  therefore,  to  exert  a 
decomposing  action  upon  water,  in  the  same  way  that  metallic 
zinc  does.  If,  then,  a  platinum  plate,  coaled  with  hydrogen  in 
the  way  above  described,  be  placed  in  acidulated  water,  and  a 
perfectly  clean  platinum  plate  be  placed  opposite  to  it,  and  the 
two. plates  be  connected  by  a  wire,  the  hydrogen  of  the  coated 
p]ate  will  tend  to  decompose  the  particle  of  water  next  it,  and 
seize  upon  its  oxygen,  forming  with  it  a  new  particle  of  water, 
and  a  state  of  polar  tension  will  be  at  once  produced  through 
the  whole  circuit,  precisely  as  there  would  be,  if  there  were  a 
zinc  plate  in  the  place  of  the  one  coated  with  hydrogen.  Under 

these  circumstances,  an 
electrical  current  will  cir- 
culate from  the  coated 
plate  to  the  clean  platinum 
through  the  liquid,  and 
then  back  through  the 
wire,  and  continue  until 
all  the  hydrogen  adhering 
to  the  coated  plate  has 
been  exhausted  by  uniting 
with  particles  of  oxygen, 
and  been  converted  into 
water.  From  this  experi- 
ment, it  appears  that  any 
substance  which  has  a 
strong  affinity  for  oxygen, 
even  though  it  be  gaseous 
in  its  character,  may  be 
used  in  place  of  an  oxi- 
dizable  metal,  as  a  gene- 
rating plate. 

339.     The    Gas    Bat- 
tery.    Advantage    has 

How  may  platinum  be  coated  with  hydro<r<>n?     Tan  such  a  coated  plate  be  used  as 
the  generating  plate  of  a  battery  ?— 339.  Describe  the  gas  battery. 

14- 


328 


THE    GAS    BATTERY. 


been  taken  of  this  property  to  form  what  is  called  a  gas  battery ; 
Fig.  143.  Two  glass  tubes,  closed  at  one  end,  have  suspended 
within  them  plates  of  platinum,  each  plate  terminating  in  a  cup 
filled  with  mercury,  placed  upon  the  summit  of  each  tube.  The 
tubes  are  first  filled  with  acidulated  water,  and  inverted  into  a 
glass  vessel  partially  filled  with  the  same  mixture.  The  tube 
marked  H,  is  then  connected  with  the  negative  pole  of  a  second 
galvanic  battery,  not  shown  in  the  figure,  and  the  tube  marked 
O,  with  the  positive  pole,  by  means  of  the  cups  filled  with  mer- 
cury, and  the  galvanic  current  passed  through  them,  descending 
through  o,  and  ascending  through  H  ;  as  the  current  passes,  the 
water  in  these  two  tubes  is  decomposed,  and  the  hydrogen  col- 
lects in  the  tube  H,  and  the  oxygen  in  the  tube  o,  gradually 
expelling  the  acidulated  water  with  which  they  are  filled,  into 
the  lower  vessel.  The  tube  H  is  made  of  twice  the  capacity 
of  the  tube  o,  and  the  process  is  continued  until  both  tubes 
are  completely  filled,  H  with  hydrogen,  and  o  with  oxygen. 
The  second  battery  is  then  entirely  removed,  and  the  two 
mercury  cups  connected  by  a  wire,  as  shown  in  the  figure. 
We  have  then  a  platinum  plate  in  the  tube  H,  surrounded 
by  hydrogen,  and  dipping  down  into  the  acidulated  water 
of  the  lower  vessel,  and  a  second  platinum  plate  in  the  tube  o, 
surrounded  with  oxygen,  and  dipping  down  into  the  acidulated 
water,  and  the  plate  in  o  connected  with  the  plate  in  H,  by  a 
wire  above.  Under  these  circumstances,  the  hydrogen  gas  in  H 
will  act  like  a  zinc  plate  similarly  situated ;  a  state  of  polar 
tension  is  at  once  produced,  running  through  the  Avhole  appa- 
ratus ;  the  lower  end  of  H  becomes  positively  electrified,  as 
shown  in  the  figure ;  it  seizes  hold  of  the  oxygen  of  the  parti- 
cle of  water  nearest  it ;  its  hydrogen  appropriates  the  oxygen 
of  the  succeeding  particle ;  and  so  on,  until  the  last  particle  of 
water  is  reached.  The  hydrogen  of  this  particle  is  discharged 
into  the  oxygen  of  the  tube,  o,  and  at  once  resolved  into  water. 
At  the  same  time,  a  current  of  positive  electricity  is  set  in  mo- 
tion through  the  liquid,  from  H  to  o,  then  up  the  plate  o  to  the 
wire,  and  finally  is  returned  to  the  plate  H,  its  course  being  indi- 
cated by  the  arrows.  As  particle  after  particle  of  hydrogen  in 
the  tube  H,  is  united  to  the  oxygen  of  successive  particles  of 
water,  fresh  portions  of  water  .are  formed  in  the  tube  H,  which 
gradually  fill  it.  At  the  same  time,  an  equal  number  of  parti- 
cles of  water  are  formed  in  the  tube  o,  by  which  it  is  also  gradu- 

Explain  how  both  tubes  become  gradually  filled  with  water. 


BATTERY    OF    INTENSITY. 


329 


ally  filled ;  and  when  this  takes  place  the  process  is  brought  to 
a  conclusion.  This  very  curious  instrument  establishes  the 
important  fact  that  hydrogen  gas  is  capable,  by  its  action  on 
acidulated  water,  of  generating  a  current  of  positive  electricity. 
By  connecting  8  or  10  such  cells  in  succession,  Fig.  144,  in 


Gas  Battery,  Compound  Circuit. 

such  a  way  that  the  oxygen  tube  of  one  cell  shall  be  connected 
with  the   hydrogen   tube  of  the  adjoining  cell,  very  decided 
manifestations  of  the  electrical  current  may  be  obtained  ;  bright 
sparks  can  be  produced  between  charcoal  points,  and  various 
chemical  decompositions  effected. 

340.   The  Galvanic  Battery.    If  the  wire  proceeding  from 
the  conducting  plate,  be  it  charcoal,  or  platinum,  or  copper,  in- 
stead  of   being 

FiS-  145-  carried  directly 

to   the    genera- 
ting zinc  plate, 
be   attached   to 
the  zinc  plate  of 
a    second    pair, 
in  a  second  ves- 
sel, as  is  repre- 
_____  _=_  sented   in    Fig. 

.     145,  the  electri- 

Crown  of  Cups,  Battery  of  Intensity.  City       generated 


340    Inscribe  the  arrangement  of  the  galvanic  battery, 
name  originally  called. 


By  whom  invented.    By  what 


330  BATTERY    OF    QUANTITY. 

by  the  first  zinc  will  be  communicated  to  the  second,  and  being 
united  to  the  electricity  generated  by  it,  will  be  transmitted 
through  the  fluid  in  the  second  vessel  to  the  second  conducing 
plate.  The  electrical  current  of  the  second  pair  is  increased 
by  the  addition  of  the  electricity  of  the  first ;  by  the  addition 
of  a  third  pair,  the  power  of  the  current  is  trebled ;  and  so  we 
may  proceed  indefinitely,  increasing  the  intensity  of  the  electri- 
cal current  by  every  additional  pair ;  but  when  we  reach  the  end 
of  the  series,  we  must  connect  the  conducting  plate  of  the  la  t 
cup  with  the  zinc,  or  generating  plate,  of  the  first  cup,  in  order 
to  make  the  circuit  complete,  and  restore  the  electrical  equilib- 
rium. Such  an  arrangement  of  connected  cups  and  plates  is;< 
called  a  Galvanic  Battery,  from  the  powerful  effects  which  it  is 
capable  of  producing.  It  was  first  devised  by  Volta,  after  his 
invention  of  the  Pile,  and  called  by  him  the  "  couronne  des 
lasses"  or,  crown  of  cups.  As  the  entire  merit  of  this  cele- 
brated instrument  belongs  exclusively  to  Volta,  and  not  at  all 
to  Galvani,  it  should  be  more  properly  called  the  Voltaic  Bat- 
tery. 

341.  Batteries  of  Intensity  and  Batteries  cf  Quantity.  It 
might  be  thought  that  an  equal  generating  surface  of  zinc 
being  employed  in  both  cases,  it  would  make  no  difference  in 
the  effect  produced,  whether  we  employed  a  great  number  of 
small  plates,  or  a  small  number  of  large  plates.  It  is  found, 
however,  in  practice,  that  there  is  an  important  difference  be- 
tween the  effects  of  the  two  arrangements.  The  former  will! 
yield  electricity  of  great  efficacy  in  effecting  chemical  decom- 
positions, the  latter,  electricity  of  great  heat-producing  power 

and  magnetic 

Fig-  146.  energy.    A  bat- 

tery that  is 
adapted  for  the: 
former  is  called 
a  Battery  of  In- 
•tensity,  and  one 
that  is  adapted 
for  the  latter  is 
called  a  Battery 
of  Quantity.  A 
battery  of  in  ten - 
Battery  of  quantity.  sity  may  be  con- 

341    What  is  a  battery  of  in  tensity?    Of  quantity?    Describe  the  arrangement  of  each.. 


IMPROVED    BATTERIES. 


331 


Ji- 


Fl 


verted  into  a  battery  of  quantity,  by  breaking  all  the  connections 
between  the  coppers  and  zincs  of  different  cups,  and  uniting  all 
the  zincs  together,  then  all  the  coppers,  and  at  last  establishing 
a  connection  between  all  the  coppers  and  all  the  zincs  by  one 
single  wire.  In  this  way  we  practically  convert  all  the  zincs 
inio  one  large  zinc,  and  all  the  coppers  into  one  large  copper 
plate;  Fig.  146. 

342.  Improved  Batteries.  Instead  of  having  the  different 
pairs  of  plates  in  different  cups,  we  may  solder  the  zinc  and 
copper  plates  together,  and  sink  them  into  grooves  in  a  trough, 
as  in  Fig.  147.  In  this  case  the  plates  themselves  form  the 

cups.     The  spa- 
Fig.  147.  ces  between  the 

plates  are  filled 
with  the  exciting 
liquid  to  the 
same  height. 
The  electricity 
generated  by  the 
first  zinc  on  the 
left  is  conveyed 
through  the  liquid  to  the  opposite  copper,  and  by  it  transferred 
to  its  companion  zinc ;  it  is  then  transmitted  through  the  next 
division  of  liquid  to  the  succeeding  copper,  and  so  through  the 
whole  series,  until  it  reaches  the  last  cell  at  A.  Into  this,  a 
conducting  copper  plate,  a,  is  inserted  and  connected  with  the 
wire  which  carries  back  the  electrical  current  to  the  beginning 
of  the  battery,  where  it  is  attached  to  another  conducting  plate, 
h,  by  which  it  is  transferred  to  the  first  zinc  plate.  In  Fig. 
148,  the  same  apparatus  is  seen  in  perspective.  It  is  called 

Fig.  148.  J 


Cruikdiank  s  Battery  in  Section. 


Cruikshantfs  Battery. 


342   Describe  the  arrangement  of  Cruikshank's  battery. 


332 


SULPHATE  OF  COPPER  BATTERY. 


Cruikshank's    Battery,  and  is  a  very  convenient  form  of  the 
apparatus. 

32.3.  The  Sulphate  of  Copper  Battery.  There  is  a  second 
form  of  the  galvanic  battery  in  which  the  liquid  to  be  decom- 
posed is  not  acidulated  water,  but  water  which  holds  in  solution 
a  quantity  of  sulphate  of  copper,  sometimes  called  blue  vitriol. 
Copper  is  employed  for  the  conducting  plate,  and  zinc  for  the 
generating  pla'e.  The  sulphate  of  copper  is  composed  of  sul- 
phuric acid  and  the  oxide  of  copper.  Sulphuric  acid  is  com- 
posed of  sulphur  and  oxygen,  and  its  composition  may  be  rep- 
resented by  SO3,  i.  e.,  one  proportion  of  sulphur,  and  three  of 
oxygen.  Oxide  of  copper  is  composed  of  copper  and  oxygen, 
and  its  symbol  is  CuO,  i.  e.,  one  proportion  of  copper,  and  one 
of  oxygen.  The  symbol  of  the  whole  is  CuO  SO3.  When 
the  zinc  plate  is  introduced  into  this  solution  it  seems  (o  produce 
a  double  decomposition,  and  at  the  same  time  set  on  foot  two 
processes  of  polarization  and  circulation  ;  Fig  149.  In  the  first 
place,  it  produces  a  chain  of  polarized 
particles  of  water,  and  second,  a  chain 
of  polarized  particles  of  sulphate  of 
oxide  of  copper,  both  extend'ng  to  the 
conducting  plate ;  then,  the  zinc  draws 
off  the  oxygen  from  the  water,  and 
the  hydrogen  seizes  upon  the  oxygen 
of  the  adjoining  particle,  as  has  been 
already  described,  until  finally  the  last 
particle  of  hydrogen  is  projected  upon 
the  conducting  plate.  The  oxide  of 
zinc  thus  formed  upon  the  zinc  plate 
seizes  upon  the  sulphuric  acid  of  the 
sulphate  of  copper  in  contact  with  it,, 
setting  free  the  oxide  of  copper,  and 
forming  sulphate  of  zinc,  which  is  at 
once  dissolved  in  the  liquid.  The 
oxide  of  copper,  thus  set  free,  seizes  upon  the  sulphuric  acid  of 
the  next  particle  of  sulphate  of  copper ;  and  thus  the  process 
goes  on,  until  finally  a  particle  of  the  oxide  of  copper  is  pro- 
jected upon  the  conducting  plate,  at  the  very  moment  when  the 
particle  of  hydrogen  just  spoken  of,  reaches  the  same  point. 
(See  the  figure.)  This  hydrogen  at  once  seizes  upon  the  oxygen 


The  Sulphate  of -Copper  Battery 
dissected. 


343  Describe  the  sulphate  of  copper  battery  What  5s  sulphate  of  copper?  Give  its 
svnibol.  What  double  decomposition  takes  place  ?  What  becomes  of  the  hydrogeu? 
Explain  the  deposition  of  the  copper.  What  is  the  advantage  of  this  battery. 


DANIELL  S    BATTERY 


333 


Tlie  Sulphate  of  Copper  Battery. 


15°-  of  the  oxide  of  copper,  forming  a  par- 

ticle of  water,  and  setting  free  metallic 
copper,  which  is  immediately  dis- 
charged upon  the  copper  conducting 
plate.  From  this,  it  appears,  that  in 
this  form  of  the  battery  the  copper 
plate  does  not  receive  a  deposit  of 
particles  of  hydrogen,  but,  in  its  place, 
a  deposit  of  copper.  Consequently, 
there  is  no  counteracting  current  of 
electricity,  produced  by  hydrogen, 
tending  to  neutralize  that  which  is 
produced  by  the  generating  plate, 
as  has  been  shown  to  be  the  case 
in  the  simple  galvanic  circuit,  and 
thus  a  great  addition  is  made  to  the  power  of  the  battery.  This 
form  of  the  galvanic  battery  is  of  special  use  for  the  production 
of  electro-magnetism,  as  will  be  shown  hereafter.  It  is  repre- 
sented in  perspective  in  Fig.  150. 

3-44.  Danicll  s  Sulphate  of  Copper  Battery.  There  is  a 
practical  difficulty  in  the  operation  of  the  sulphate  of  copper 
battery,  that  the  zinc  plate,  is  itself  more  or  less  covered  by  the 
particles  of 'reduced  copper,  which  act  as  so  many  secondary 
conducting  plates,  and  tend  to  dissipate  the  force  of  the  princi- 
pal current,  and  divert  it  into  smaller  channels.  Another  diffi- 
culty consists  in  the  decomposition  of  the  sulphate  of  zinc  by  the 
operation  of  the  current,  and  the  deposition  of  metallic  zinc 
u;)on  the  copper  plate,  thus  converting  it  practically  into  a  zinc 
plate,  and  causing  it  to  set  up  a  counter  current.  These  diffi- 
culties are  overcome  by  separating  the  zinc  plate  from  the  cop- 
per plate  by  the  intervention  of  a  porous  cup,  and  thus  pre- 
venting the  sulphate  of  copper  from  coming  into  direct  contact 
with  the  zinc,  and  the  sulphate  of  zinc  with  the  copper.  This 
j  form  of  the  instrument  constitutes  Darnell's  battery,  and  the 
arrangement  is  as  follows;  Fig.  151.  z  represents  a  solid  bar 
of  zinc,  placed  in  a  cup  of  porous  earthen  ware,  and  filled  with 
acidulated  water ;  c  represents  the  copper  plate,  made  in  the 
form  of  a  cylindrical  cup,  open  at  the  top,  and  closed  at  the 
bottom,  and  filled  with  a  solution  of  sulphate  of  copper.  On 
the  inner  side  of  the  rim  of  this  cup  is  supported  a  copper  shelf, 
pierced  with  holes,  for  the  purpose  of  containing  some  crystals 

344-  What  are  some  of  the  difficulties  connected  with  the  operation  of  the  common 
battery?    Describe  Daniell's  battery. 


Fig.  151. 


Danieirs  Battery  Dissected. 


DISSECTED. 

of  sulphate  of  copper,  which,  by  its 
gradual  dissolving,  may  maintain  the 
strenglh  of  the  sulphate  of  copper  so- 
lution placed  below.     As  soon  as  the 
zinc  and  copper  plates  are  connected 
by  a  wire,  a  steady  current  of  elec- 
tricity begins  to  circulate,  which  will 
continue    to    flow    for    many    hour?. 
The  zinc,  as  soon  as  it  is  introduced 
into  the  acidulated  water,  decomposes 
it  in  the  usual  manner,  and  the  libera- 
ted hydrogen  is  carried  towards  the 
conducting  plate,  directly  through  the 
porous  cup.     As  soon  as  it  enters  the 
sulphate  of  the  oxide  of  copper,  it 
seizes  upon  the  oxygen  of  the  oxide, 
and  is  re-converted  into  water,  giving  up  its  electricity  at  the 
same  moment  to  the  copper  of  the  oxide,  which  is  at  once  de- 
posited upon  the  surface  of  the  copper  cylinder.     The  sulphuric 
acid  which  is  set  free  from  the  sulphate  of  copper,  represented 
in  the  figure  by  SO3,  finds  its  way  into  the  porous  cup,  where  it 
assists  in  keeping  up  the  strength  of  the  acid  solution,  and  is  ulti- 
mately converted    into    sulphate  of   zinc    by  uniting  with  the 
oxide  formed  upon  the  surface  of  the  zinc  rod.     The  porous 
cup,  though  it  is  sufficiently  firm  to  prevent  the  two  liquids  from 
mingling,  opposes  no  impediment  to  the  passage  of  the  hydrogen 
through  it  in  one  direction,  and  of  the  sulphuric  acid  in  the 
other,  by  the  polarization  of  the  chain  of  liquid  particles  which 
penetrates  it.     By  this  arrangement,  the  hydrogen  is  prevented 
from  reaching  the  copper  plate  and  setting  up  a  counteracting 
current,  arid  the  copper  set  free  from  the  oxide,  cannot  pass 
through  the   porous  cup  and  attach  itself  to   the   zinc  plate. 
At  the   same   time,  the    sulphate  of  zinc   is   prevented   from 
passing  over  to  the  copper,  depositing  metallic  zinc,  and  con- 
verting  it  practically  into  a   second   zinc   plate,  directly  op- 
posed to  the  first.     The  result  is,  that  such  a  battery  will  keep 
up  a  steady  current  of  electricity  for  many  hours,  and  hence  is 
often  called  the  constant  battery.     The  actual  form  of  this  bat- 
tery is  shown  in  Fig.  152.     v  represents  a  glass,  or  earthen- 
ware jar ;    G,    the    copper    cylinder,  pierced    with    holes ;     c, 


What  becomes  of  the  hydrogen?    How  is  the  copper  plate  prevented  from  being  cor- 
ered  with  zinc  ? 


GROVE  S    BATTERY. 


335 


Daniell's  Battery. 


Fig-  152-  the  colander,  filled  with  crystals 

of  sulphate  of  copper ;  p,  the  po- 
rous cup ;  z,  the  rod  of  zinc ;  p 
and  n  are  thin  strips  of  copper,  for 
connecting  with  other  cells.  In 
this  battery,  the  hydrogen  is  re- 
moved by  chemical  means. 

3£5.  Grove's  Battery.  In 
this  battery,  the  hydrogen  is  also 
removed  by  chemical  means,  and 
it  depends  for  its  action  upon  the 
peculiar  effect  of  this  substance  on 
nitric  acid.  This  acid  is  a  com 
pound  of  nitrogen  and  oxygen,  and 
may  be  represented  by  the  symbol 
l^O5,  i.  e.,  five  proportions  of  oxy- 
gen, to  one  of  nitrogen.  Hydrogen 
discharged  into  this  substance,  decomposes  it  by  appropriating 
one  proportion  of  oxygen,  forming  water,  and  converting  NO5 
into  NO4,  or,  nitric  into  nitrous  acid.  The  latter  differs  from  the 
former,  in  po^e^sirig  a  deep  red,  or  mahogany  color,  and  emitting 
d;jep  red  acid  fumes.  By  this  action,  the  hydrogen  is  transferred 
from  the  gaseous  into  the  liquid  state.  In  Grove's  battery,  the 
conducting  plate  is  made  of  platinum,  and  is  immersed  in  a  po- 
rous cup,  of  clay,  filled  with  strong  nitric  acid,  and  placed  in  the 
centre  of  a  zinc  cylinder,  surrounded 
by  acidulated  water.  In  Fig.  153,  z 
represents  the  zinc  cylinder,  open  at 
both  ends,  and  placed  in  a  jar  of  glass 
or  earthen-ware,  filled  with  acidula- 
ted water ;  p  represents  the  platinum 
plate,  placed  in  the  interior  of  the 
porous  cup,  filled  with  strong  nitric 
acid.  The  hydrogen,  set  free  by 
the  zinc,  instead  of  being  permitted 
to  strike  directly  upon  the  platinum 
plate,  passes  through  the  porous  cup 
into  the  nitric  acid,  where  it  is  con- 
_^  verted  into  water  by  uniting  with 

one  proportion  of  the   oxygen  con- 
Battery,  Dissected.         tained  in  the  acid,  as  represented  in 


Fig.  153. 


345.  Describe  Grove's  battery.     With  what  liquid  is  the  porous  cup  fillet!? 

14* 


356 


BUNS  EN'S    BATTERY. 


the  figure,  and  converting  it  into  nitrous  acid;  at  the  same 
moment,  it  yields  up  its  electricity  to  the  nitrous  acid,  by 
which  it  is  conveyed  to  the  conducting  platinum.  By  this  pro- 
cess, the  nitric  is  rapidly  changed  into  nitrous  acid,  a  substance 
emitting  a  large  quantity  of  red  and  acid  fumes,  and  is  also 
rapidly  diluted  by  the  drops  of  water  steadily  added  to  it. 
The  strength  of  the  nitric  acid  is  therefore  continually  diminish- 
ing, and  the  constant  action  of  this  battery  is  not  so  great  as 
Daniell's.  By  the  complete  and  energetic  absorption  of  the  hy- 
drogen in  this  battery,  power  is  amazingly  increased,  and  it 
constitutes  the  best  form  of  the  instrument,  being  distinguished 
for  the  steadiness  and  intensity  of  its  action;  and  12  or  24  cups 
of  it  are  quite  sufficient  for  performing  all  the  most  brilliant 
galvanic  experiments.  In  order  to  use  several  cups  at  once,  tlie 

platinum  plate  of  one  pair 
must  be  connected  with 
the  zinc  of  the  succeed- 
ing pair,  and  the  termi- 
nating jolar  wires  at- 
tached, one  of  them  to 
the  extreme  platinum, 
and  the  other  to  the  ex- 
treme zinc  plate.  The 
actual  form  of  the  in- 
strument is  seen  in  Fig. 
154,  where  z  represents 
the  zinc  cylinder,  sur- 
rounded by  acidulated 
water;  v,  the  porous 
cup,  filled  with  nitric 
Battery.  acid,  and  containing  the 

platinum  plate,  p  ;  b  and 

«,  are  screws,  for  the  attachment  of  wires.  This  battery  dis- 
charges a  large  amount  of  acid  fumes,  and  it  should  always  be 
placed  in  the  open  air,  or  in  the  strong  draught  of  a  chimney. 

346.  Eunsen's  Battery.  It  is  not  necessary  that  the  con- 
ducting plate  be  made  of  metal ;  any  good  conductor  of  elec- 
tricity will  answer  equally  well.  Advantage  is  taken  of  this 
in  Bunsen's  battery,  which  resembles  Grove's,  exactly,  except 
in  the  substitution  of  carbon  cylinders  for  the  platinum  plates. 


What  becomes  of  the  hydrogen  ?    What  is  said  of  the  intensity  and  constancy  of  this 
battery  ?— 346.  Describe  Bunsen's  battery. 


SMEE'S   BATTERY. 


337 


Fig-  155.  Carbon  is  an  excellent  conductor 

of  electricity,  and  on  account  of 
its  great  cheapness,  compared 
with  platinum,  which  is  a  very 
expensive  metal,  is  much  to  be 
preferred.  The  form  of  the  ap- 
paratus is  much  larger.  The 
carbon  cylinders  are  composed  of 
solid  gas  coke,  found  in  the  inte- 
rior of  illuminating-gas  retorts, 
or  else  of  powdered  coke,  mixed 
with  sugar,  and  baked.  Porous 
cups,  of  corresponding  size,  filled 

Bimsen's  Battery.  with  nitric  acid,  are  used.    These 

batteries  are   sold   in    Paris  for 
about  5  Francs  the  cup.     Fig.  155. 

347.    Smee's  Battery.     This  form  of  the  battery  is  also 
designed  to  increase  power  by  favoring  the  escape  of  the  hydro- 

gen. It  does  so,  however,  by  me- 
chanical  means,  instead  of  chemi- 
cal, and  not  so  perfectly  as  in  Grove's 
and  Bunsen's  batteries.  It  has  been 
found  that  the  bubbles  of  hydrogen 
adhere  with  considerable  force  to 
the  smooth  surfaces  of  conducting 
plates,  but  escape  readily  from  the 
angles  and  edges.  The  conducting 
plate  in  Smee's  battery  is  made  of 
silver,  roughened  by  the  deposition 
upon  it  of  spongy  platinum  from 
some  solution  in  which  it  has  been 
dissolved,  and  by  this  roughness  of 
surface  the  discharge  of  the  gas  is 
much  facilitated.  Fly.  156. 

348.  Management  of  Batteries. 

In  all  these  batteries,  it  is  to  be  noted  that  the  real  source  of 
the  electric  current  is  the  decomposition  of  water  by  zinc; 
but  this  water  must  be  acidulated  with  sulphuric  acid  in  the 
proportion  of  1  part,  by  measure,  of  acid,  to  8  parts  of  water. 
When  very  energetic  action  is  required,  the  solution  may  be 
made  stronger.  As  great  heat  is  produced  on  mingling  the  acid 


Battery. 


317.  Describe  Smee's  battery. — 348.  What  precautions  must  be  adopted  iu  the  manage- 
ment of  batteries  ? 


338  MANAGEMENT    OF    BATTERIES. 

and  water,  the  mixture  should  be  made  some  time  before  use, 
and  allowed  to  cool.  The  nitric  acid  should  be  the  strongest 
that  can  be  procured,  and  never  diluted.  It  is  always  decom- 
posed by  the  action  of  the  battery,  producing  a  ~large  quantity 
of  corrosive  fumes,  and  should  not  be  employed,  therefore,  in  a 
closed  room,  or  in  one  in  which  there  is  any  nice  apparatus.  It 
is  essential  that  the  zincs  be  well  amalgamated  by  dipping  them 
info  mercury,  upon  the  surface  of  which  floats  a  quantity 
of  diluted  chlorohydric  acid,  (muriatic  acid.)  The  zinc  is 
cleaned  as  it  passes  through  the  dilute  acid,  and  the  mercury 
immediately  amalgamates  with  it,  giving  it  a  bright  and  smooth 
surface.  They,  should  always  be  thoroughly  washed  in  abun- 
dance of  pure  water,  after  use  in  the  battery.  The  wires  for 
connections  should  be  of  copper,  well  annealed,  so  as  to  be  very 
flexible.  The  ends  of  these  wires  should  be  carefully  bright- 
ened with  a  file,  or  by  amalgamation  with  mercury  before  at- 
tachment to  the  binding  cups  ;•  in  all  cases,  the  ends  of  the  bind- 
ing screws  should  be  brightened  by  a  file,  pr  sand  paper,  before 
use,  and  all  metallic  connections  carefully  examined.  Not  un- 
frcqiu'ntly  the  action  of  a  very  powerful  battery  is  greatly 
impeded,  or  entirely  stopped,  by  a  slight  film  which  has  formed 
on  some  connecting  surface.  Where  the  electrical  charge  is  to 
be  passed  through  water  for  the  purpose  of  decomposing  it,  the 
wa:er  must  ise  acidulated.  It  is  advantageous  to  have  the  coup- 
}  ngs  of  the  cells  of  a  battery  arranged  in  such  a  way  that '.it 
can  be  used  either  as  a  battery  of  intensity,  or  a  battery  of 
quantity.  The  effects  of  these  arrangements  are  widely  dif- 
ierent,  as  will  be  seen  hereafter.  If  it  is  desiredl^Tise  a  bat- 
tery of  intensity,  the  conducting  plate  of  the  first  cell  should  be 
connected  with  the  generating  plate  of  the  second  cell,  and  so 
on,  in  a  regular  series,  as  represented  in  Fig.  157.  On  the 

Fig.  157. 


Arrangement  of  a  Battery  of  Intensity. 


other  hand,  if  a  battery  of  quantity  be  desired,  the  generating 
plates,  i.  e.,  the  zincs,  of  all  the  cells,  should  be  connected  to- 
gether, and  the  conducting  plates  in  the  same  manner,  as  rcpre- 


of  quantity  ? 


DE    LUC  S    PILE. 


339 


Fig.   158. 

T 


Arrangement  of  a  Battery  of  Quantity. 

sented  in  Fig.  158.  By  such  an  arrangement,  the  various  zinca 
practically  become  one  large  zinc  plate,  and  the  various  con- 
ducting plates  one  large  conducting  plate,  and  the  quality  of  the 
electricity  produced  is  materially  changed. 

3  3:9.  De  Luc's  Pile.— Dry  Pile.  This  is  a  galvanic  arrange- 
ment, not  requiring  the  use  of  any  liquid,'  and  named  from  its 
invenfor.  It  was  introduced  shortly  after  the  invention  of  the 
voltaic  pile.  It  coasists  of  a  number  of  alternation^,  of  very 
thin  sheets  of  metal,  with  paper  interposed  between  them. 
Thin  paper,  coated  with  gold  or  silver  leaf  on  one  side,,  should 
b3  covered  on  the  uncqated  side  with  thin  zinc  foil.  This  paper 
should  then  b3  punched  out  into  circular  discs  of  about  an  inch 
in  diameter,  and  these  arranged  in  such  a  wa^  that  the  same 
order  of  succession,  viz.,  zinc,  paper,  silver,  zinc,  paper,  silver, 
should  be  preserved  throughout,  exactly  as  the  discs  are  arranged 
in  the  voltaic  pile.  From  500  to  1000  such  pairs  are  required 
to  produce  an  active  column,  and  they  are  most  conveniently 
pi  iced  in  a  glass  tube,  perfectly  clean  and  dry  within,  and  sur- 
mounted at  each  end  by  a  bra^s  cap,  perforated  by  a  screw, 
which  may  serve  to  compress  the  discs,  and  also  act  as  the 
poles  of  the  pile,  the  screw  at  one  end  being  in  contact  with  the 
silvered  side  of  the  disc,  and  constituting  the  po-itive  pole,  and 
that  at  the  other  with  the  zinc  disc*,  and  forming  the  negative 
pole.  The  electrical  current  in  this  pile  is  due  to  the  slight 
oxidation  of  the  zinc  discs  by  the  moisture  contained  in  the 
paner.  If  the  paper  be  artificially  dried,  the  pile  loses  its  ac- 
tivity, but  again  recovers  its  energy  as  the  paper  re-absorbs 
mo'sture  from  the  air.  Provided  the  two  extremities  of  this 
pile  remain  unconnected,  it  will  reta'n  its  activity  for  years  ;  but 
if  the  two  poles  are  connected  by  a  wire,  the  zinc  discs  become 

319    Describe  Pe  Luc's  dry  pile      To  what  is  the  electrical  current  in  De  Luc's  pi'e 
due?     What  Ls  the  effect  of  drying  the  paper  artificially? 


340  GALVANIC    AND    STATICAL 

gradually  oxidized,  and  the  electrical  power  is  destroyed.  With 
a  De  Luc's  pile  containing  20,000  discs  of  zinc  paper  and  sil- 
ver, sparks  have  been  obtained,  and  a  Ley  den  battery  charged 
sufficiently  to  produce  shocks.  A  more  effective  instrument  is 
prepared  by  using  finely  powdered  peroxide  of  manganese,  in 
place  of  the  gold  or  silver  leaf.  One  surface  of  the  paper  disc 
is  coated  with  zinc,  the  other  with  the  peroxide,  either  dry  or 
attached  by  honey  and  water.  A  metallic  plate  is  placed  at 
each  end  for  a  conductor  and  the  whole  series  is  tied  together 
b|f  silk  thread ;  the  outside  is  then  coated  by  dipping  it  in  melted 
sulphur.  The  superior  power  of  this  instrument  depends  upon 
the  affinity  of  the  hydrogen,  produced  by  the  action  of  the  zinc 
upon  the  moisture  of  the  paper,  for  the  oxygen  of  the  peroxide, 
in  virtue  of  which  it  is  reconverted  into  water,  and  the  paper 
kept  continually  moist. 

330.  Proof  of  the  similarity  of  the  electricity  of  the  Hat- 
tsry  and  that  cf  the  Electrical  machine.  The  relation  be- 
tween the  electricity  of  the  voltaic  battery  and  that  of  the  elec- 
trical machine,  may  be  readily  ascertained  by  means  of  a  De 
Luc's  pile.  On  applying  such  a  pile,  containing  500  or  1000 
discs,  by  that  extremity  which  is  in  contact  with  the  last  silver 
disc,  and  which,  consequently,  represents  the  end  of  the  con- 
ducting plate  in  the  common  voltaic  battery,  to  the  knob  of  the 
gold  leaf*  electroscope,  Fig.  115,  whose  leaves  have  been  made 
to  diverge  with  positive  electricity,  its  leaves  will  still  continue 
divergent.  If  the  opposite,  or  zinc,  end  of  the  pile  be  then  ap- 
plied to  the  electroscope,  its  divergent  leaves  will  first  coPapfe, 
and  then  diverge  again.  Consequently,  we  infer,  (see  §  #07, 
]).  280,)  that  the  silver  end  of  the  pile,  or  the  conducting  end 
of  the  common  battery,  is  excited  with  positive,  and  the  zinc 
erad  with  negative  electricity.  Thus  a  connection  is  established 
between  the  electricity  of  the  conducting  end  of  the  battery,  and 
that  of  the  prime  conductor  of  the  electrical  machine,  and  the 
electricity  of  the  zinc  end  and  that  of  the  rubber  of  the  Fame 
machine.  If  the  wires  attached  to  the  two  ends  of  a  De  Luc's 
pile  be  made  to  terminate  in  two  small  discs,  which  are  brought 
within  an  inch  and  a  half  of  each  other,  and  carefully  insulated, 
an  insulated  slip  of  gold  leaf,  suspended  midway  between  the 
two  discs,  will  first  be  attracted  to  the  po-itSve  disc,  then  repelled 
and  attracted  towards  the  negative  disc,  and  thus  a  state  of  per- 

Explain  the  use  of  paper  coated  with  the  peroxide  of  manganese  in  place  of  the  silver 
leaf  ?— 350.  How  may  the  similarity  of  the  electricity  of  the  battery,  and  that  of  the  elec- 
trical machine,  be  proved  by  De  Luc's  pile?  How  may  it  be  proved  by  the  ordinary 
battery  ? 


ELECTRICITY    COMPARED.  341 

petual  oscillation  produced  which  will  continue  uninterruptedly 
for  months  or  years.  The  oppositely  electrified  state  of  the  two 
poles  of  the  voltaic  pile  may  also  be  shown  with  the  ordinary 
battery,  by  attaching  the  wire  connected  with  one  pole  of  a 
powerful  battery  to  the  foot  of  the  electroscope,  and  the  wire 
connected  with  the  other  pole  to  the  knob  or  plate  of  the  instru- 
ment, the  gold  leaves  will  diverge  powerfully,  the  platinum  end 
furnishing  positive,  and  the  zinc  end  negative,  electricity. 

351.  The  difference  between  Galvanic  and  Statical  Elec- 
tricity-    Galvanic  electricity  differs  essentially  from  that  of  the 
electrical  machine  in  possessing  feeble  intensity ;  and  therefore 
but  little  power  of  overcoming  obstacles  placed  ii  its  path,  giv- 
ing shocks  and  the  like.     It  is  incapable  of  producing  many  of 
the  effects  of  the  electrical  machine,  and  its  influence  upon  elec- 
trometers and  electroscopes  is  extremely   slight.     A  Leyden 
jar  can  only  be  charged  with  great  difficulty  by  making  a  com- 
munication between  one  of  its  surfaces  and  one  pole  of  the  bat- 
tery, while  the  other  surface  is  connected  with  the  opposite  pole. 
When  the  polar  wires  are  brought  near  each  other,  only  a  feeble 
spark  will  pass,  and  on  establishing  the  communication  between 
them  by  means  of  the  hands  previously  moistened,  a  shock  is 
felt,  but  only  for  a  moment.     On  the  other  hand,  it  is  developed 
in  much  larger  quantity  than  ordinary  electricity,  and  in  a 
steadily  flowing  current;  it  possesses,  also,  heating  power  of 
much  greater  intensity,  extraordinary  powers  of  chemical  decom- 
po;ition,  and  a  wonderful  influence  in  producing  magnetism. 
Moreover,  if  the  current  from  a  powerful  battery  be  passed 
through  the  great  centres  of  the  nervous  system,  the  most  aston- 
ishing muscular  contractions  are  excited.     It  is  capable  of  pro- 
ducing, therefore,  remarkable  heating,  chemical,  magnetic,  and 
physiological  effects. 

352.  Galvanic  Batteries  of  Historic  Note.    Among  memo- 
rable apparatus  of  this  class  which  have  obtained  celebrity  in 
the  history  of  physical  science,  may  be  mentioned  the  pile  of 
2000  pairs  of  plates,  each  having  a  surface  of  32  square  inches, 
at  the   Royal  Institution,  London,  with  which   Sir   H.  Davy 
made  his  great  discovery  of  the  decomposition  of  the  alkalies, 
— potash  and  soda ;  also  the  great  pile  of  the  Royal  Society, 
of  nearly  the  same  magnitude.     In  1808,  the  Emperor  Napo- 
leon presented  to  the  Polytechnic  School,  at  Paris,  a  battery  of 

351.  State  the  chief  points  of  difference  as  to  intensity,  quantity,  chemical  decompose 
tion,  magnetic  influence,  &c..  between  the  electricity  of  the  machine,  and  that  of  tb,» 
battery.— 352.  Mention  some  of  the  galvanic  batteries  of  historic  note. 


342  HISTORIC    BATTERIES. 

600  pairs  of  plates,  having  each  a  square  foot  of  surface.  It 
was  with  this  apparatus  that  several  of  the  most  important 
researches  of  Gay  Lussac  and  Thenard,  were  conducted.  Chil- 
dren's great  battery,  in  London,  consisted  of  1  6  pairs  of  plates, 
each  plate  measuring  6  feet  in  length,  and  2§  feet  in  width,  FO 
that  the  copper  surface  of  each  amounted  to  32  square  feet ; 
and  when  the  whole  was  connected,  there  was  an  effective  sur- 
face of  512  square  feet.  Dr.  Hare's  Deflagrator,  in  Philadel- 
phia, consisted  of  80  pairs  of  plates,  each  zinc  surface  measur- 
ing 54  square  inches,  and  each  copper  80  square  inches.  Pej  y's 
battery,  at  the  London  Institution,  consisted  of  pairs  of  enor- 
mous size,  composed  of  a  sheet  of  copper,  and  a  sheet  of  zinc, 
measuring  each  50  feet  in  length,  and  2  feet  in  width.  These 
were  wound  round  a  rod  of  wood  with  horse  hair  between  them. 
Each  bucket  conta:ned  55  gallons  of  the  exciting  liquid.  With 
these  batteries  most  extraordinary  effects  were  produced. 
When  the  poles  were  dipped  beneath  the  surface  of  water,  a 
large  quantity  of  oxygen  and  hydrogen  was  produced,  and  the 
water  speedily  grew  very  hot ;  iron  wire  melted  and  fell  down 
in  globules,  and  steel  burned  with  brilliant  scintillation  •.  Wiih 
Children's  great  battery  many  substances  were  fused  which  were 
exposed  to  the  best  wind  furnaces  without  any  effect.  A  p'ece 
of  platinum  wire,  l-30th  of  an  inch  in  diameter,  and  18  inches 
long,  became  instantly  red,  then  white  hot,  with  a  brilliancy  in- 
supportable to  the  eye,  and  in  a  few  seconds  was  fused  into 
globules.  When  charcoal  points  were  attached  to  the  poles  of 
the  battery  of  the  Royal  Institution,  a  magnificent  display  of 
light  was  produced,  the  flame  darting  from  one  point  to  the  oilier 
when  they  were  four  inches  apart,  and  curving  upwards  in  an 
arch.  When  any  substance  was  held  in  this  arch  it  became 
instantly  ignited,  platinum  was  melted  in  it,  like  wax  in  a  can- 
dle, quartz,  sapphire,  magnesia,  lime,  all  fused,  arid  the  diamond 
and  plumbago  entered  into  combustion  and  disappeared  in  the 
air.  These  batteries,  however,  and  all  similar  apparatus,  power- 
ful as  they  were,  and  memorable  as  the  discoveries  in  physics 
are  to  which  they  have  been  instrumental,  have  fallen  into  disuse 
since  the  invention  of  the  batteries  of  Grove  and  Daniell,  with 
two  liquids.  These,  with  a  number  of  pairs  of  plate*,  not  ex- 
ceeding 40,  and  exposing  a  surface  not  exceeding  100  square 
inches  each,  produce  a  power  equal  to  the  largest  of  the  batteries 
above  described. 

Describe  the  effects  produced  by  Children's  battery,  and  that  of  the  Koyal  Institution. 
Why  are  fruese  great  batteries  no  longer  used  ? 


HEATING    AND    LUMINOUS 

353.  Heating-  effects  of  the  Galvanic  Current.    In  all  cases 
where  electricity  is  in  motion,  the  force  is  conveyed  by  the  en- 
tire thickness  of  the  conductor,  and  not  by  the  surface  alone. 
If  the  wire  connecting  the  poles  of  a  small  galvanic  battery  be 
made  to  pass  through,  or  be  carried  around,  the  bulb  of  an  a  r 
thermometer,  as  soon  as  the  current  circulates,  a  very  perceptible 
effect  will  be  produced  upon  the  instrument.     If  the  battery  be 
large,  and  the  wire  small,  the  latter  will  become  very  hot,  some- 
times be  made  red-hot,  and  actually  melted.     This  is  owing   o 
the  smallness  of  the  diameter  of  the  conducting  wire,  by  which 
a  large  quantity  of  the  electrical  current  is  compelled  to  traverse 
a  limited  number  of  conducting  particles  in  a  given  time.     The 
rise  of  temperature  in  the  wire  is  inversely  proportional  to  its 
conducting  power,  and  therefore  the  poorer  the  conductor,  the 
greater  the  heat  produced.     This  may  be  shown  by  forming  a 
chain  of  alternate  links  of  silver  and  platinum,  and  transmitting 
through  it  a  current  from  a  powerful  battery.     The  silver  being 
a  good  conductor  of  electricity,  and  not  obstructing  the  passage 
of  the  current,  exhibits  no  intense  hea*,  while  the  links  of  plati- 
num, in  consequence  of  the  poor  conducting  power  of  that  metal, 
almost  immediately  become  red-hot.     The  conducting  power  of 
the  metals  for  electricity  varies  nearly  in  the  same  order  as  their 
power  of  conducting  heat.     Charcoal,  however,  though  a  bad 
conductor  of  heat,  is  an  exceedingly  good  conductor  of  electri- 
city.   Elevation  of  temperature  diminishes  the  conducting  power 
of  the  metals.     This  may  be  proved  by  transmitting  through  n 
platinum  wire  a  galvanic  current  sufficient  to  make  it  red-hot ; 
and  while  the  current  is  still  passing,  igniting  a  small  part  of 
the  wire  by  the  flame  of  a  spirit  lamp ;  the  rest  of  the  wire 
immediately  ceases  to  glow,  in  consequence  of  the  obstruction 
at  the  point  of  ignition,  and  the  Consequent  diminution  in  the 
flow  of  the  current. 

354.  Ignition  produced.    The  heat  produced  by  the  elec- 
trical current  may  rise  so  high  as  to  produce  ignition  of  the 
most  refractory  substances.     Carbon  is  the  only  substance  which 
can  not  be  melted  by  the  pile,  though  with  six  hundred  Bvmsen 
cells  it  has  been  softened  to  such  a  degree  that  adjoining  pieces 
will  adhere,  which  seems  to  indicate  the  commencement  of  fusion. 

3r)3.  How  may  the  heat  of  the  connecting  wire  be  shown  by  an  air  thermometer? 
What  effect  is  produced  upon  the  heat  of  the  wire  by  reducing  its  size ••''.  To  what  is  the 
rise  of  temperature  in  the  wire  inversely  proportional?  How  may  this  bo  shown  by  a 
ch;iin  of  alternate  links  of  platinum  and  silver?  What  effect  Iris  Novation  of  tempera- 
ture on  the  cooductjug  power  of  the  mutais  / — 354.  Describe  cases  of  j^iiition  produced 
by  the  current, 


344  EFFECTS    OF    THE    CURRENT. 

Platinum,  which  can  not  be  melted  by  the  most  intense  heat  of  a 
wind  furnace,  is  immediately  made  white-hot,  and  fused  by  a 
powerful  battery.  It  is  said  that  if  two  platinum-poin'ed  pen- 
cils, connected  with  the  poles  of  the  battery,  be  presented  point 
to  point,  so  that  the  current  may  pass  between  them,  they  will 
be  fused  and  soldered  together,  and  that  this  effect  will  be 
equally  produced  under  wa'er.  The  other  metals  are  not  only 
melted,  but  volatilized,  and  dissipated  in  vapor.  Iron  and  pla- 
tinum burn  with  a  shining  white  light;  lead,  with  purple;  tin 
and  gold,  with  bluish  light ;  zinc,  with  white  and  red ;  copper 
and  silver,  with  a  greeni-h  light.  These  effects  are  displayed 
with  increased  splendor  if  the  metal  to  be  burned  be  attached 
to  a  wire  connected  with  the  positive  pole,  and  then  applied  to 
the  surface  of  mercury  connected  with  the  negative  pole.  If 
a  piece  of  steel  watch  spring,  thus  attached,  be  brought  near  the 
surface  of  a  cup  of  mercury  connected  with  the  negative  pole, 
the  most  beautiful  scintillations  will  be  produced ;  a  steel  file 
will  answer  nearly  the  same  purpose.  If  two  steel  or  iron 
wires,  connected  with  the  two  poles,  be  brought  near  each 
other,  vivid  sparks  will  pass  from  one  to  the  other,  and  if  they 
both  be  coated  with  lamp-black,  by  holding  them  in  the  flame 
of  an  oil  lamp,  the  sparks  will  be  much  brighter,  especially 
if  the  two  wires  be  held  opposite  each  other,  directly  in  the 
flame  of  the  lamp. 

355.  Luminous  effects.  All  combustible  substances,  whether 
solid  or  liquid,  such  as  ether,  alcohol,  phosphorus,  and  gunpow- 
der, may  be  inflamed  by  passing  the  galvanic  current  through 
them.  A  platinum  wire,  several  yards  in  length,  can  be  made 
to  glow  With  intense  brilliancy;  and  the  effect  is  greatly  in- 
creased if  the  wire  be  wound  into  the  form  of  a  spiral  helix. 
Oxygen  and  hydrogen  gases ;  also,  hydrogen  and  chlorine,  are 
combined  by  the  spark,  with  a  bright  flash,  and  loud  explosion. 
When  pieces  of  well  burned  charcoal  are  attached  to  the  wires, 
and  become  the  poles  of  the  battery,  on  bringing  them  near 
each  other,  a  most  brilliant  arc  of  flame,  emitting  the  brightest 
artificial  light  known,  flashes  between  them.  The  compact 
coke  of  gas  retorts  is  better  adapted  to  this  purpose  than  any 
other  form  of  charcoal.  The  points  must  be  brought  near  each 
other,  and  then  gradually  separated,  Fig.  159  ;  a  is  the  positive 
pole,  b  the  negative.  As  they  are  drawn  apart  by  the  rack  and 

How  may  the  splendor  of  the  light  produced  by  the  burning  metals  be  increased  ?— • 
355.  Describe  the  luminous  effects  produced  by  charcoal  points.  What  arrangement  of 
the  points  increases  the  luminous  effect  ? 


DUBOSCQ'S  ELECTRIC  LIGIIT. 


345 


Fig-  159.  pirron,  the  light 

and  flame  still 
continue,  assum- 
ing the  form  of  a 
curved  arc.  If 
the  different  met- 
als are  placed  in 
this  flame  they 
are  volatilized  at 
once,  and  pass 
off  in  fumes.  So 
intense  is  the 
light,  that  it  may- 
be used  in  opti- 
cal experiments 
in  place  of  the 
light  of  the  sun. 
The  luminous  ef- 
fect is  found  to 
be  increased  if 
the  upper  piece 
of  carbon  be 
made  the  posi- 
tive, and  the  lower  the  negative  pole.  And  if  the  two  carbon 
points  are  arranged  in  a  horizontal  position,  at  right  angles  to 
the  magnetic  meridian,  the  length  of  the  luminous  arc  is  said  to 
be  greater  in  the  proportion  of  20.8  to  16.5,  when  the  positive 
pole  is  to  the  east,  than  when  it  is  to  the  west. 

356.  Duboscq's  Electric  lamp.  During  the  production 
of  this  dazzling  light  there  is  a  considerable  transport  of  the 
particles  of  carbon  from  the  positive  to  the  negative  pole.  A 
cavity  is  always  produced  in  the  carbon  connected  with  the  posi- 
tive pole,  and  a  deposit,  continually  increasing  in  length,  is 
formed  upon  the  negative  pole.  In  Fig.  160  is  represented  an 
exceedingly  ingenious  apparatus  for  keeping  this  light  at  a  fixed 
point  in  space  so  that  it  may  be  used  in  the  solar  microscope. 
Ordinarily  the  position  of  the  light  is  continually  changing  as 
the  negative  pole  is  increasing  at  the  expense  of  the  positive ; 
and  this  unfits  it  for  use  in  connection  with  lenses ;  but  in  this 
apparatus  this  difficulty  is  overcome,  and  when  placed  in  the 

356  "What  change  takes  place  in  the  length  of  the  charcoal  points  during  the  passage 
of  the  current?  If  the  position  of  the  light  be  made  fixed,  for  what  purpose  may  it  be 
used?  Describe  Fig-  160. 


Luminous  Effects  of  the  Battery. —  Charcoal  Points. 


346  NOT    PRODUCED    BY    COMBUSTION. 

Fig.  160. 


Duboscq^s  Electric  Lamp. 


microscope,  the  image  of  the  two  points  is  formed  upon  a 
screen  at  some  distance,  upon  an  enlarged  scale.  From  this 
image,  as  shown  in  the  figure,  the  peculiar  shape  assumed  by 
the  two  poles  can  he  plainly  seen,  and  also  the  process  of  trans- 
port, by  which  one  increases  at  the  expense  of  the  other.  This 
exceedingly  elegant  instrument  is  the  invention  of  M.  Duboscq, 
of  Paris,  and  is  intended  to  be  used  in  the  performance  of  opti- 
cal experiments,  in  place  of  solar  light. 

357.  Discovery  of  the  Electric  Light  Sir  H.  Davy,  in 
1801,  at  London,  was  the  first  to  perform  the  experiment  cf 
the  electric  light,  and  with  the  great  battery  of  the  Royal  In- 
stitution, consisting  of  2000  pairs  of  plates,  obtained  an  arc 
of  flame  between  two  charcoal  points,  4  inches  in  length.  This 
charcoal  had  been  prepared  by  heating  it  red-hot,  and  then 
quenching  it  beneath  the  surface  of  mercury.  Despretz,  how- 
ever, with  600  cells  of  Bunsen,  arranged  consecutively,  suc- 
ceeded, when  the  points  were  placed  vertically,  the  positive 
pole  being  above,  in  obtaining  an  arc  7.8  inches  in  length. 

358-  The  Electric  Light  is  not  produced  by  Combustion. 
That  this  is  not  a  case  of  ordinary  combustion  of  charcoal  in 
air,  simply  increased  by  the  action  of  the  galvanic  current,  may 


357.  Who  was  the  discoverer  of  the  elertric  light  ?  What  results  did  he  a  ttain  ? 
length  of  arc  was  obtai.-.ed  by  Despreta  ? — 358.  Show  that  the  electric  light  is  i 
duced  by  coinbustiou 


Wh:.t 
not  pro. 


INTENSITY    OF    THE     ELECTKIC    LIGHT. 


q  «  7 

0-17 


Fig.  161. 


be  shown  by  placing  the  charcoal  points  in  the  interior  of  a 
glass  vessel,  from  which  the  air  has  been  withdrawn  by  the  air 
pump,  Fig.  161.  It  will  be  found  that  the  light  is  quite  a-; 
great  as  before.  It  can  even  be  produced 
beneath  the  surface  of  water,  but  is  consider- 
ably diminished  in  splendor.  The  light  is  in 
great  part  due  to  the  continued  transport  of 
minute  particles  of  carbon  in  a  state  of  in- 
tense incandescence. 

359.  The  properties  and  intensity  of  ths 
Electric  Light.  The  heat  produced  in  the 
voltaic  arc  is  of  the  most  intense  kind.  Pla- 
tinum, iridium,  and  titanium,  which  resist  the 
greatest  heat  of  the  most  powerful  wind  fu  - 
nace,  readily  melt,  when  placed  in  it.  The 
light  is  powerful  enough  to  produce  the  com- 
bination of  chlorine  and  hydrogen  at  a  con- 
siderable distance,  and  without  any  direct  con- 
tact, and  to  act  upon  the  chloride  of  silver,  i:i 
the  same  way  as  the  light  of  the  Fun.  It  also 
po-sesses  the  singular  property  of  being  at- 
tracted by  the  magnet.  Transmitted  through 
a  prism,  the  electric  light  is  decomposed,  and 
produces  a  spectrum  like  that  of  the  sun,  with 
lines  analogous  to  the  lines  of  Fraunhofer,  ex- 
cept that  they  are  bright,  instead  of  dark. 
The  character  of  these  lines  depends  upon 
the  metal  with  which  the  poles  are  tipped.  The  light  produced 
by  18  cells  of  Bunsen,  has  been  estimated  as  more  than  that 
proceeding  from  572  candle*;  under  the  mo  t  favorable  circum- 
stances, it  has  been  computed  as  equal  to  one-third  of  the  inten- 
sity of  solar  light,  and  is  so  bright  that  it  can  not  safely  be  re- 
girded  by  the  naked  eye. 

363.  Connection  between  the  heat  of  the  Battery  and  the 
mechanical  equivalent  of  Heat.  The  chemical  action  within 
the  battery  always  produces  heat,  and  a  definite  amount  of 
chemical  action  a  definite  amount  of  heat ;  no  more  and  no  less. 
It  has  been  ascertained,  however,  that  if  heat  is  developed 
at  any  point  in  the  circuit  outside  the  battery,  the  amount  cf 
heat  produced  within  the  battery  is  diminished  in  an  equal  ratio, 

359  What  degree  of  heat  ia  produced  by  the  voltaic  arc?  Of  light?  If  the  light  l>e 
transmitted  through  a  glass  prism,  what  may  be  observed?  How  docs  it  compart!  v.-itli 
the  light  of  the  sun  ? — 3'iO.  If  a  portion  of  fie  power  of  fie  battery  be  used  to  produce 
motion,  wiiat  uil'ect  is  produced,  upon,  tke  lieat  of  tiie  battery  1 


Charcoal  Points  in 
Vac  no. 


348  THE    CHEMICAL    EFFECTS    OF    THE    CURRENT. 

and  that  if  the  electrical  current  be  used  to  produce  motion,  as 
it  may  be,  when  employed  to  generate  electro-magnetism,  a  por- 
tion of  the  heat  of  the  entire  circuit  disappears,  having  been  con- 
verted into  mechanical  effect  or  motion.  The  quantity  of  heat 
which  disappears  corresponds  very  nearly  to  that  which  Joule's 
law,  (§  254,)  would  require  for  the  production  of  an  equal  mechan- 
ical effect.  This  serves  to  confirm,  very  strongly,  the  mechanical 
theory  of  heat. 

361.  Heating-  effects  are  best  produced  by  batteries  of 
quantity.    In  experiments  on  the  heating  effects  of  the  galvanic 
current,  the  battery  should  be  arranged  ?o  that  the  zinc  plates 
may  all  be  connected  together,  practically  forming  but  one  zinc 
plate,  and  the  platinum  plates,  in  the  same  manner,  forming  but 
one  platinum  plate,  as  shown  in  Fig.  158. 

362.  The  chemical  effects  of  the  galvanic  current.— Its  de- 
composing1 power.    The  chemical  effects  of  the  voltaic  current 
are  even  more  remarkable  and  interesting  than  the  heating.     It 
had  been  noticed  in   Holland,  in  1798,  that  a  succession  of 
charges  of  statical  electricity  transmitted  for  a  long  time  through 
water,  by  means  of  platinum  or  gold  conductors  which'  nearly 
touched  each  other,  effected  the  decomposition  of  water;  and 
in  1800,  shortly  after  the  invention  of  the  voltaic  pile,  it  was 
discovered  by  Nicholson    and  Carlisle,  two  English  chemists, 
that  a  current  of  galvanic  electricity  would  not  only  decompose 
water,  but  that  the  oxygen  would  invariably  be  discharged  at 
the  positive  pole,  and  the  hydrogen  at  the  negative.     This  ex- 
periment led  to  the  application  of  the  galvanic  current  to  other 
chemical  compounds,  with  a  view  to  effect  their  decomposition, 
and  enabled  Sir  H.  Davy,  a  few  years  afterwards,  to  decompose 
the  alkalies,  potash  and  soda,  which  heretofore  had  been  re- 
garded as  simple  substances,  and  to  prove  that  they  were  com- 
posed of  oxygen,  and  two  different  metals,  potassium  and  sodium. 
This  great  discovery  was  the  prelude  to  others  of  a  similar  kind, 
and  led  to  the  establishment  of  an  entirely  new  theory  in  regard 
to  the  constitution  of  the  various  rocks,  minerals,  earths,  and 
salts,  of  which  the  earth  is  composed,  viz.,  that  they  all  possess 
a  metallic  basis,  and  have  been  produced  by  the  combination  of 
different  metals  with  other  simple  substances,  chiefly  gaseous. 

,       363.    The  constitution  of  Water.    Pure  water  is  a  compound 

Is  there  any  correspondence  between  the  amount  of  heat  thus  conTerted  into  motion, 
and  that  which  is  required  by  Joule's  law?— 3G1.  Which  kind  of  battery  produces  the 
greatest  heating  effect .' — 332.  Who  discovered  the  chemical  effect  of  the  current  ?  Wh:;t 
use  did  Sir  II.  Davy  make  of  it  ? — 333.  Describe  the  composition  of  water  by  volume,  and 
by  weight,  as  shown  by  its  decomposition 


THE    DECOMPOSITION    OF    WATER  349 

of  two  gaseous  chemical  elements,  oxygen  and  hydrogen,  and 
hence  is  called  a  binary  compound.  It  is  al  o  composed  of  these 
substances,  united  in  certain  definite  proportions,  both  by  weight 
and  by  volume.  By  weight,  the  proportion  of  oxygen  to  hy- 
drogen is  8  to  1 ;  by  volume,  it  is  as  1  to  2.  Hence,  if  we  wish 
to  produce  water  by  the  cornbinatio  i  of  these  two  substances, 
we  must  use  8  parts  by  weight  of  oxygen,  to  1  part  by  weight 
of  hydrogen ;  but  by  volume,  1  measure  of  oxygen,  to  2  meas- 
ures of  hydrogen  ;  and  these  8  parts  by  weight  of  oxygen,  com- 
bined with  1  part  by  weight  of  hydrogen,  make  exactly  9  parts 
by  weight  of  pure  water.  On  the  other  hand,  if  we  decompose 
pure  water,  we  always  obtain  one  volume  of  oxygen,  to  two 
volumes  of  hydrogen,  and  every  9  grains  of  water  decomposed 
produce  just  8  grains  of  oxygen,  and  1  grain  of  hydrogen. 
From  this,  it  appears  that  the  proportions  in  which  elements 
un'te,  by  weight,  to  form  compounds,  are  very  different  from  the 
proportions  in  which  they  unite  by  volume.  When  one  volume 
of  oxygen,  and  two  volumes  of  hydrogen,  or  which  is  the  same 
th'ng,  eight  parts  by  weight  of  oxygen,  and  one  part  by  weight 
of  hydrogen,  are  introduced  into  a  closed  receiver,  and  a  spark 
from  the  electrical  machine  is  passed  through  them,  an  explosion 
re  ults,  the  gases  disappear,  and  watery  vapor  is  formed,  which, 
on  the  cooling  of  the  vessel,  condenses  into  little  drops  of  water. 
The,  weight  of  the  water  formed  is  always  precisely  equal  to  the 
sum  of  the  weights  of  the  two  gases  employed. 

364.  The  decomposition  of  Water  by  the  Battery.  If  two 
platinum  or  gold  wires  be  attached  to  the  poles  of  the  battery, 
and  then  be  brought  near  each  other  beneath  the  surface  of 
water  slightly  acidulated  with  sulphuric  acid,  bubbles  of  oxygen 
gas  will  appear  at  the  positive,  and  of  hydrogen  at  the  negative 
pole.  If  tubes,  closed  at  the  upper  end,  ana  open  at  the  lower, 
be  completely  filled  with  water,  so  as  to  retain  no  bubbles  of  air 
whatever,  and  then  inverted  over  each  pole,  the  bubbles  of  each 
ga>  as  they  arise,  will  be  collected  separately  in  the  two  tubes, 
tli"}  oxygen  in  the  tube  over  the  positive  pole,  and  the  hydrogen 
in  that  over  the  negative  pole,  and  twice  as  much  of  the  latter  as 
of  the  former;  Fig.  162.  As  the  hydrogen  is  collected  in  double 
the  quantity  of  the  oxygen,  the  tube  containing  it  should-  be  made 
twice  as  large  as  that  for  oxygen  ;  the  process  may  be  continued 
till  both  are  filled ;  and  this  will  take  place  at  the  same  instant. 

Can  w?ter  be  reproduced  by  uniting  these  elements  iu  tae  same  proportions  1 — 854. 
Desc.ibe  the  decomposition  of  water  by  ti.e  curreut. 


350 


EFFECTED    BY    THE    POLARIZATION 


Fig.   162. 


Decomposition  of  Water. 


On  carefully  closing  the 
oxygen  tube  beneath 
the  water,  and  invert- 
ing it,  so  that  a  lighted 
taper  can  be  introduced 
into  it  from  above,  the 
taper  will  be  found  to 
burn  with  extraordi- 
nary splendor,  and  if 
blown  out  in  such  a  way 
as  to  leave  a  small 
smou'dering  spark  upon 
the  wick,  it  will  be  re- 
lighted when  it  is  intro- 
duced again  into  the 


gas.  On  the  other  hand,  if  the  hydrogen  tube  be  lemoved  with 
equal  care,  but  not  inverted,  and  a  lighted  taper  introduced  into 
it  from,  below,  the  hydrogen  will  take  fire,  and  bum  with  a  lam- 
bent flame,  but  the  taper  will  be  extinguished.  Thus,  the:  e  two 
ga^es  may  be  distinguished  by  their  opposite  effects  upon  a 
lighted  taper.  If,  instead  of  using  two  tube?,  one  tube  be  nTed 
with  water,  and  inverted  over  both  poles,  the  two  gases  will  be 
colected  together,  and  if  a  spark  from  the  electrical  machine  be 
passed  through  the  mixture,  there  will  be  a  flash  of  1'ght,  and 
an  explosion  ;  the  two  gases  will  unite  to  Ibrm  a  very  small  por- 
tion of  water,  and  will  entirely  disappear,  and  the  water  from 
the  vessel  will  rush  up  so  as  to  completely  fill  the  wl.ole  of  the 
tube.  In  performing  this  experiment,  it  is  necessary  to  use  a 
platinum  wire  for  the  positive  pole  at  which  the  oxygen  is  dis- 
charged, for  if  a  copper  wire  be  employed,  or  any  other  metal 
which  has  a  strong  affinity  for  oxygen  ,  the  gas  will  unite  with 
the  metal  to  form  a  solid  oxide,  instead  of  escaping  and  ris'ng 
through  the  liquid.  Platinum  and  gold  have  only  a  very  slight 
affinity  for  oxygen,  and,  therefore,  when  these  are  used,  nearly 
the  whole  of  the  gas  is  collected.  It  is  advantageous  in  all  such 
experiments  to  have  bolh  wires  made  of  p^tinum.  From  this 
experiment,  it  is  evident  that  the  galvanic  current  has  the  power 
of  decomposing  water,  and  separating  it  into  its  constituent  ele- 
ments. 

365.   The  decomposition  of  Water  is  effected  by  the  polari- 
zation and  transfer  of  the  component  elements-     It  has  been 


Which  gas  collects  in  the  larger  quantity?    How  may  they  be  tested,  and  proved  to 
be  different  ?     Y»~ny  must  tue  decomposing  wires  be  made  of  platinum  t 


AND    TRANSFER    OF    THE    ELEMENTS. 


351 


of  Water. 


already  stated  that  the  galvanic  influence  is  propagated  by  a 
polarization  of  the  liquid,  as  well  as  the  solid,  part  of  the  whole 
circuit.  When  the  two  platinum  wires  are  dipped  into  the 
acidulated  water,  the  liquid  becomes  a  part  of  the  circuit,  and 
the  part  cles  between  the  poles  become  polarized ;  so  that  the 
atoms  of  oxygan  are  all  turned  towards  the  positive,  and  the 
atoms  of  hydrogen  towards  the  negative  pole,  in  the  manner 
represented  in  Fig.  163.  On  the  right,  the  polarized  platinum 

wire,  P,  connected  with  the 
163-  zinc  end  of  the  battery,  z, 

enters  a  vessel  of  acidula- 
ted water,  represented  in 
section.  On  the  left,  a 
similar  platinum  wire,  P, 
connected  with  the  copper 
end  of  the  battery,  enters 
the  same  vessel  of  water. 
The  polarized  wire,  P  z, 
on  theright,is  then  the  negative  po^  of  the  battery,  and  the 
polarized  wire,  P  c,  is  the  positive  pole.  In  consequence  of  the 
highly  excited  negative  electricity  accumulated  in  p  z,  all  the 
atoms  of  hydrogen  in  the  chain  of  particles  of  water  being 
naturally  charged  with  positive  electricity,  are  drawn  towards 
it ;  and  all  the  atoms  of  negative  oxygen  are  repelled  from  it, 
and  at  the  same  time  attracted  towards  the  positively  excited 
platinum  wire,  P,  c  ;  on  the  principle  that  bodies  electrified  dif- 
ferently attract  each  other,  while  those  electrified  similarly  repel 
one  another.  The  next  instant,  the  superior  negative  excite- 
ment of  the  wire  completely  separates  the  atom  of  hydrogen 
from  the  atom  of  oxygen,  and  as  it  can  not  unite  with  the  pla- 
tinum, it  is  discharged  into  the  water,  and  escapes  into  the  air. 
At  the  same  moment,  the  negative  oxygen  at  the  opposite  ex- 
tremity of  the  chain  is  drawn  powerfully  towards  the  positive 
platinum  wire,  and  as  it  can  not  unite  with  the  platinum,  it  is 
also  discharged,  and  escapes  into  the  air.  This  necessitates  a 
movement  throughout  the  whole  chain,  and  a  flow,  in  opposite 
directions,  of  the  two  gases,  and  also  of  the  negative  and  posi- 
tive current.  It  is  obvious,  from  the  figure,  why  it  is  necessary 
that  the  positive  pole  should  be  made  of  some  unoxidizable 
metal ;  if  it  were  no^,  tho  oxygen  discharged  upon  it  would 
unite  with  it  to  form  a  solLl  oxide,  and  there  would  be  no  escape 


365.  Describe  Fig.  lf>3.     Show  that  the  decomposition  of  the  water  depends  upou  the 
polarization  of  tV  circuit.     Why  is  the  water  acidulated? 

15 


352  THE    DECOMPOSITION    OF    METALLIC    OXIDES 

"< 

of  gas.  Jf  the  oxide  be  insoluble,  it  may  adhere  to  the  pole, 
forming  a  crust  upon  it ;  in  this  case,  if  the  oxide  be  a  cor  due!  or 
of  electricity,  it  will  itself  become  the  pole ;  if  it  be  not  a  <  on- 
ductor,  it  will  interfere  with,  and  finally  arrest  the  course  of  che 
current,  and  put  an  end  to  the  decomposition.  If  the  oxide  be 
soluble,  it  will  be  dissolved  as  fast  as  formed,  and  the  water  will 
become  a  solution  of  the  oxide.  If  the  water  contain  acid,  the 
acid  will  unite  with  the  oxide  to  form  a  new  substance,  and  the 
liquid  will  become  a  solution  of  this  substance.  In  tie  experi- 
ment just  described,  the  sulphuric  acid  is  not  ifrelf  cleeompored, 
but  it  tends  to  favor  the  passage  of  the  current  through  the 
water.  It  is  exceedingly  difficult  for  the  electrical  current  to 
pass  at  all  through  pure  water,  but  on  adding  from  one  to  fifteen 
per  cent,  of  acid,  its  passage  is  greatly  facilitated.  Common 
salt,  dissolved  in  water,  produces  the  same  effect.  These  sub- 
stances all  seem  to  act  by  lessening  the  affinity  which  binds  the 
part'cles  of  oxygen  and  hydrogen  to  each  other. 

366.  The    decomposition    of    other    compound    U.quids. 
Water  is  not  the  only  substance  susceptible  of  electrical  decom- 
position;  a  large  number  of  compound  liquids  may  be  decom- 
posed in  a  similar  manner.     It  is  always  necessary  that  the  sub- 
stance shou'd  be  a  liquid,  or  soluble  in  a  liquid,  otherwise  there 
can  be  no  transfer  of  the  elements  which  it  conta:ns  on  account 
of  their  immobility.     If  water  be  solidified,  it  immediately  ar- 
rests the  passage  of  the  current.     A  sold  sub  tan ce  can  not  be 
decomposed  in  this  manner ;  but  sometimes,  merely  moistening 
a  solid,  will  be  sufficient  to  allow  the  transfer  of  its  elements. 
Binary  compounds,  or  those  which  consist  of  one  atom  of  each 
element,  are  those  which  are  most  readily  decomposed,  as  is 
seen  in  the  case  of  water.     In  like  manner,  chloro-hydric  acid, 
a  compound  substance,  composed  of  chlorine  and  hydrogen,  and 
whose  symbol  is  HC1,  is  readily  polarized  and  decomposed  by 
the  electrical  current ;  the  chlorine  being  discharged  at  the  posi- 
tive pole,  and  the  hydrogen  at  the  negative.     Ammonia,  com- 
posed of  nitrogen  and  hydrogen,  and  whose  symbol  is  NH3,  is 
also  easily  decomposed,  the  nitrogen  collecting  at  the  positive 
pole,  and  the  hydrogen  at  the  negative. 

367.  The  decomposition  of  Bffietallic  Oxides  in  solution. 
Oxygen  unites  with  most  of  the  metals  to  form  a  new  class  of 
substances  called  oxides.     Thus,  common  iron  rust  is  a  com- 

3G6.  Why  must  the  compound  substance  to  be  decomposed  be  in  the  liquid  state  ? 
Mention  various  compound  liquids  which  may  be  decomposed  by  the  current.— 567.  De- 
scriU;  tut-  decomposition  of  tae  metallic  oxides,  potash  and  soda. 


AND    SALTS.  353 

/ 

pound  of  iron  and  oxygen ;  soda  is  a  compound  of  the  metal 
sodium  and  oxygen ;  potash  is  a  compound  of  the  metal  potassium 
and  oxygen.  Many  of  these  oxides  are  soluble  in  water,  and 
some  of  (hern  can  be  decomposed  by  the  galvanic  current.  In 
all  these  case^  the  metal  appears  at  the  negative,  and  the  oxy- 
gen at  the  positive  pole.  Thus,  if  perfectly  pure  potash,  moist- 
ened, and  placed  upon  a  platinum  plate,  connected  with  the 
negative  pole  of  the  battery,  be  touched  with  a  platinum  wire 
connected  with  the  positive  pole,  small  metallic  globules  of  pure 
potassium  will  be  formed  upon  the  platinum  plate,  and  oxygen 
will  be  discharged  upon  the  wire.  The  same  is  true  of  soda 
and  sodium.  If  the  platinum  be  formed  into  a  cup,  and  filled 
with  mercury,  and  the  potash  be  placed  upon  it,  the  potassium 
amalgamates  with  the  mercury  as  fast  as  formed,  and  may  l}e 
obtained  pure  by  distillation  in  an  atmosphere  of  nitrogen. 

353.  The  decomposition  of  Metallic  Salts  in  Solution.  The 
metallic  oxides  are  capable  of  uniting  with  acids,  to  form  a  class 
of  substances  called  salts.  Thus  potash,  or  the  oxide  of  potas- 
sium, can  unite  with  sulphuric  acid,  to  form  the  sulphate  of 
potash.  In  like  manner,  the  oxide  of  copper  can  unite  with 
sulphuric  acid,  to  form  the  sulphate  of  copper ;  the  oxide  of  lead 
can  unite  with  acetic  acid,  to  form  the  acetate  of  lead;  the 
oxiJe  of  silver  with  nitric  acid,  to  form  the  nitrate  of  silver. 
These  salts,  if  dissolved  in  water,  can  often  be  decomposed  by 
the  galvanic  current,  and  in  all  cases,  the  acid  appears  at  the 
positive,  the  metallic  oxide  at  the  negative  pole ;  sometimes, 
however,  the  oxide  itself  is  also  decomposed,  and  then  its  oxy- 
gen joins  the  acid,  and  appears  at  the  positive  pole,  while  the 
metal  alone  appears  at  the  negative  pole. 

369  The  Decomposing:  Tube.  These  decompositions  can 
be  very  clearly  shown  by  the  apparatus  represented  in  Fig.  1 64. 
It  is  a  glass  tube,  curved  twice  at  right  angles.  The  liquid,  or 
solution  to  be  decomposed,  is  poured  into  it,  and  the  poles  in- 
serted, one  in  each  leg.  They  should  be  of  platinum,  and  long 
enough  to  reach  the  curve,  so  as  to  come  as  near  as  possible  with- 
out touching.  On  pouring  into  such  a  tube, — technically  called 
a  U  tube, — a  solution  of  sulphate  of  soda,  mixed  with  a  little 
tincture  of  blue  violets,  the  salt  will  be  decomposed.  The  sul- 
phuric acid  will  be  di-charged  at  the  positive  pole,  and  will 
change  the  blue  color  of  the  solution  to  red ;  while  the  soda  will 

368  Describe  the  decomposition  of  metallic  salts.  At  which  pole  does  the  acid  appear? 
At  which  the  oxide  ? — 3fJ9  Describe  the  decomposing  U  tube,  and  the  experiments  that 
may  bu  performed  with  it. 


354 


THE    DECOMPOSING   TUBE. 


Decomposing  U  Tube. 


164«  be  collected  at  the  negative  pole, 

and  will  change  the  blue  color  of 
that  tube  to  green.  On  disconnect- 
ing the  wires  from  the  battery,  and 
agitating  the  tube  so  as  to  mix  the 
two  colors,  the  original  blue  will 
be  restored.  If  sulphate  of  copper 
be  introduced,  the  sulphuric  acid 
will  be  discharged  in  one  leg  and 
the  oxide  of  copper  in  the  o.her. 
If  a  solution  of  nitrate  of  silver  be 
introduced,  the  nitric  acid  will  be 
discharged  at  one  pole,  and  the 
oxide  of  silver  at  the  other;  if 
acetate  of  lead  be  employed,  the  acetic  acid,  and  oxygen  from 
the  oxide,  will  appear  in  one  tube,  and  the  pure  lead  in  the 
other.  If  a  solution  of  iodide  of  potassium  be  used,  the  iodine 
will  appear  in  the  positive  tube,  and  the  potassium  in  the  nega- 
tive ,  and  the  presence  of  the  iodine  may  be  detected  by  pouring 
in  a  little' solution  of  starch,  which  will  at  once  be  turned  to  a 
deep  blue ;  the  potassium  will  be  immediately  converted  into 
potash  by  uniting  with  the  oxygen  of  the  water,  and  its  pres- 
ence may  be  shown  by  pouring  in  blue  tincture  of  violets,  which 
will  at  once  be  changed  to  a  bright  green.  The  same  apparatus 
will  answer  equally  well  for  the  decomposition  of  chloro-hydric 
acid ;  the  chlorine  will  appear  in  the  positive  tube,  and  may  be 
detected  by  its  odor  and  bleaching  effect  upon  a  few  drops  of 
solution  of  indigo,  and  the  hydrogen  will  appear  in  the  negative 
tube.  In  like  manner,  if  acidulated  water  be  introduced,  the 
oxygen  will  be  discharged  in  the  positive  tube,  and  the  hydrogen 
in  the  negative  ;  and  if  the  end  of  the  leg  be  stopped  with  a  cork, 
through  which  passes  a  tube  of  glass,  drawn  to  a  fine  aperture, 
the  hydrogen,  as  it  escapes,  may  be  lighted,  and  will  burn  at 
the  end  of  the  tube  with  a  small,  but  a  steady  flame. 

370.  Glass  Cup  with  Porous  Diaphragm.  The  same  ex- 
periments may  be  well  performed  with  the  apparatus  delineated 
in  Fig.  1G5,  Jt  consists,  simply,  of  a  glass  cup,  divided  in  the 
middle  by  a  porous  diaphragm  of  plaster,  confined  in  a  frame, 
as  represented  in  a.  This  porous  diaphragm,  inasmuch  as  it 
allows  the  penetration  of  liquids,  and  therefore  of  the  establish- 

What  is  the  effect  when  sulphate  of  soda  is  decomposed  ?  Iodide  of  potassium  ?  fhlo- 
ro-hydrjc  acjd?  Water?  HOW  may  the  hydrogen  be  burned?— 370.  Describe  the  de, 
composing  cell,  and  the  experiments  which  may  be  performed  with  it. 


SECONDARY  355 

165>  ment  of  a  chain  of 

liquid  particles 
through  it,  offers  no 
obstacle  to  the  pass- 
age of  the  electric 
current,  and  the  con- 
sequent transfer  of 
Ceil.  elements  in  both  di- 

rections through  it. 
In  the  decomposition  of  salts  into  acids  and  oxides,  the  acid  will, 
in  all  cases  appear  at  the  positive,  and  the  oxide  at  the  negative 
pole,  and  be  manifested,  one  in  each  cell.  The  presence  of  the 
acid  may  bs  detected  by  pouring  into  the  positive  cell  some  t<nc- 
ture  of  a  vegetable  blue,  like  that  of  blue  violets,  when  the  blue 
color  will  immediately  be  turned  to  red.  If  the  oxides  formed 
belong  to  the  peculiar  class  called  alkalies,  their  presence  will  be 
indicated  in  the  negative  cup,  by  turning  the  same  vegetable  blue 
to  green.  Thus,  if  a  solution  of  carbonate  of  potash,  or  sulphate 
of  soda,  or  nitrate  of  lime  be  introduced  into  the  glass  cup, 
and  colored  blue  by  the  vegetable  tincture,  it  wi.l  be  turned  red 
in  the  cell  into  which  the  positive  pole  dips,  and  green  in  the 
cell  containing  the  negative  pole;  because  lime,  soda,  and  pot- 
ash, are  alkaline  oxides,  and  have  the  peculiar  faculty  of  turn- 
ing vegetable  blues  to  green.  But  if  a  solution  of  the  nitrate 
of  silver,  the  sulphate  of  copper,  and  the  sulphate  of  iron,  be 
introduced  into  the  glass  cup,  with  the  addition  of  the  same 
vegetable  solution,  it  will  be  turned  red  by  the  acids  set  free  in 
the  positive  cell,  but  will  remain  unchanged  in  the  negative  ce'l, 
because  the  oxides  of  silver,  copper,  and  iron  are  insoluble,  and 
therefore  manifest  no  alkaline  properties. 

371.  Secondary  Decomposition.  When  the  poles  of  the 
battery  are  made  of  platinum,  or  some  other  equally  unoxidiza- 
ble  metal,  and  the  substance  to  be  decomposed  is  a  binary  com- 
pound, composed  of  two  elements  only,  and  it  is  used  in  a  pure 
state,  there  being  no  other  compound,  or  elementary  substan:  e, 
of  any  kind,  present,  then  the  decomposing  action  of  the  cur- 
rent is  of  the  simple  character  already  described ;  but  it  is  not 
often  that  the  substances  decomposed  are  thus  situated.  In  the 
ease  of  most  of  the  solids  which  have  been  spoken  of,  they  are 
used  in  the  state  of  solution  in  water,  and  therefore,  by  the  ac- 
tion of  the  galvanic  current,  the  water  may  be  decomposed  as 

871'  What  is  meant  by  secondary  decomposition.  ? 


356 


DECOMPOSITION. 


well  as  the  salt  in  question,  and  the  oxygen  thus  set  free  at  one 
pole,  and  the  hydrogen  at  the  other,  may  have  a  very  important 
effect  upon  the  other  substances  which  appear  at  the  same  points. 
If,  for  instance,  sulphate  of  copper,  in  solution  in  water,  be  the 
substance  to  be  decomposed,  as  soon  as  it  is  subjected  to  the 
action  of  the  electrical  current,  sulphuric  acid  will  be  set  free 
at  one  pole,  and  oxide  of  coppe^  p,t  the  other ;  but  at  the  same 
time,  a  second  current  will  be  established,  operating  through  the 
particles  of  water,  and  the  result  is,  that  hydrogen  will  be  dis- 
charged at  the  same  pole  with  the  oxide  of  copper,  and  oxygen 
at  the  same  pole  with  the  sulphuric  acid.  The  hydrogen  will 
at  once  attack  the  oxide  of  copper,  and  uniting  with  its  oxygen, 
will  form  water,  and  the  copper  will  be  deposited  upon  the  pla- 
tinum pole ;  at  the  other  pole,  the  oxygen  which  is  set  free, 
having  nothing  with  which  it  can  unite,  is  discharged  into  the 
air.  Consequently,  in  most  cases  of  the  decompositron  of  salts 
in  solution,  instead  of  the  oxide  of  the  metal  being  set  free  at 
the  negative  pole,  the  metal  in  a  pure  state  is  deposited  in  con- 
sequence of  this  secondary  action  of  the  hydrogen.  This  sec- 
ondary action  is  indicated  in  Fig.  166,  where  the  twro  platinum 

poles  of  a   battery,  p  +, 
166-  and  P  — ,  are  inserted  in  a 

solution  of  sulphate  of  cop- 
per, represented  by  the 
upper  circle,  CuO  SO3 ; 
the  whole  of  the  liquid  is 
supposed  to  be  composed 
of  similar  globules,  mixed 
with  globules  of  water,  HO. 
One  row  of  these  globules 
is  represented  as  polarized,  the  positive  oxide  of  copper,  CuO, 
being  turned  towards  the  negative  platinum  pole,  and  the  nega- 
tive sulphuric  acid,  SO3,  turned  towards  the  positive  pole.  Im- 
mediately beneath  this  row,  is  another,  composed  of  particles  of 
water,  also  polarized,  the  hydrogen  being  turned  towards  the 
negative,  while  the  oxygen  is  turned  towards  the  positive  plati- 
num pole.  The  instant  the  current  begins  to  circulate,  the  oxide 
of  copper  is  drawn  to  the  negative  pole,  and  at  the  same  moment 
the  globule  of  hydrogen  is  also  attracted  to  the  same  point ;  the 
hydrogen  immediately  seizes  upon  the  oxygen  of  the  oxide,  and 


Secondary  Decomposition. 


What  is  the  effect  of  the  decomposition  of  the  water  at  the  same  time  with  that  of  me- 
tallic salts?  Illustrate  this  as  shown  by  Fig.  16G,  in  the  case  of  sulphate  of  copper. 
What  ia  the  general  effect  of  hydrogen  on  metallic  oxides  set  free  at  the  negative  pole? 


EXPERIMENT  OF  THREE  CUPS.  357 

r 

escapes  into  the  liquid  in  the  form  of  water,  while  the  copper, 
baing  de-erted  by  the  oxygen,  is  deposited  in  the  form  of  a  film 
of  metallic  copper  upon  the  platinum  conductor.  At  the  oppo- 
site pole,  sulphuric  acid  is  discharged,  and  at  the  same  point  oxy- 
gen gas ;  the  former  is  at  once  taken  up  by  the  water,  while  the 
latter,  being  in  the  gaseous  state,  rises  through  the  liquid,  and 
passes  off  into  the  air.  As  water  is  present  in  almost  all  cases 
of  the  decomposition  of  chemical  substances,  it  is  evident  that 
secondary  action  may  be  generally  looked  for,  and  there  are  few 
ca-es  of  decomposition  in  which  it  is  not  concerned.  We  shall 
presently  see  the  importance  of  this  action  in  all  cases  of  elec- 
tro-plating. 

372.  Experiment  of  three  Cups  connected  by  Syphons. 
These  effects  will  also  take  place  even  if  the  solution  is  put  in 
two  distinct  cups,  placed  side  by  side,  provided  only  they  be 
connected,  by  syphons  of  glass  filled  with  the  same  liquid,  and 
establishing  a  communication  between  the  cups.  The  metal,  in 
this  case,  will  appear  in  one  cup,  and  the  acid  in  the  other. 
Moreover,  if  three  cups,  as  in  Fig.  167,  be  used,  and  connected 

together  by  syphons,  or  by 

Fig.  167.  shreds  of  asbestos,  moistened 

with  the  solution  employed, 
and  a  solution  of  sulphate  of 
soda  be  introduced  into  all 
the  cups,  colored  by  a  vege- 
table blue,  the  acid  will  be 
found  in  the  extreme  right 
hand  cup,  c,  with  which  the 

positive   pole    is    connected, 
^—m™™.*™,  an^  ^.jj  ^^^  .^  r^  while 

the  soda  will  be  found  in  the 
extreme  left  hand  cup,  A,  and  will  turn  it  green,  without  the  slight- 
est change  produced  upon  the  blue  color  of  the  middle  cup,  B,  not- 
withstanding the  electric  current  must  have  passed  through  it. 
This  very  singular  result  is  explained  by  the  polarization  of  the 
entire  circuit,  in  virtue  of  which,  not  a  particle  of  acid  or  alkali  is 
set  absolutely  free  in  their  passage  in  opposite  directions  through 
the  m'ddle  cup,  until  they  reach  the  platinum  poles;  conse- 
quently, no  effect  is  produced  by  either  upon  the  color  of  the 
middle  cup,  though  both  pass  through  it.  If  the  poles  be  re- 
versed, i.  e.,  if  the  right  hand  cup  be  connected  with  the  nega- 

372.  Describe  the  experiment  of  the  three  cups  connected  by  syphons.    How  may  this 
be  explained  by  polarization  ? 


oa»  SIR  H.  DAVY  s  EXPERIMENTS. 

five  end  of  the  battery,  instead  of  the  positive,  the  acid  will  be 
collected  in  the  left  hand  cup,  and  the  alkali  in  the  one  on  the 
right.  This  will  be  manifested  by  the  changes  in  the  color  of 
the  infusion*.  The  liquid  in  c,  which  had  been  reddened  by 
the  acid,  will  first  recover  its  original  color  in  consequence  of 
the  neutralizing  effect  of  the  alkali,  and  will  then  become  green 
as  the  alkali  accumulates.  In  like  manner,  the  liquid  in  A, 
which  had  been  turned  green,  will  gradually  recover  its  original 
blue  color,  and  then  become  reddened  as  the  acid  accumulates 
beyond  the  amount  required  to  neutralize  the  alkali.  During 
all  these  transfers,  no  change  will  be  observed  in  the  intermedi- 
ate cup,  B. 

373.  Sir  H.  Davy's  extraordinary  experiment,  in  which 
acids  and  alkalies,  while  under  the  influence  of  the  current, 
seem  to  lose  their  ordinary  affinity.     Sir  H.  Davy  ascertained 
that  if  the  middle  cup,  B,  be  filled  with  a  strong  alkaline  solu- 
tion, for  which  the  various  acids  have  a-  powerful  affinity,  they 
may  be  transferred  by  the  electrical  current  through  this  alkali, 
without  any  combination  taking  place  between  them.     Thus,  if 
sulphate  of  soda  be  placed  in  A,  Fig.  1 67,  and  in  B,  a  solution  of 
potash,  for  which,  ordinarily,  sulphuric  acid  has  a  very  powerful 
affinity,  and  pure  water  be  placed  in  c,  as  soon  as  c  is  connected 
with  the  posidve  pole,  and  A  with  the  negative,  the  sulphuric  acid 
will  be  transported  through  the  potash  in  B,  without  uniting 
with  it,  and  make  its  appearance  in  c.     The  same  acid  may 
thus  be  transported    through  ammonia,  and  solutions  of  lime 
and  soda,  without  affecting  them,  and  so,  in  like  manner,  chloro- 
hydric  and  nitric  acids.     This  result  is  explained,  as  in  the  pre- 
vious case,  by  the  polarization  of  the  entire  circuit,  in  virtue  of 
which,  not  a  particle  of  acid  is  set  free  after  it  leaves  the  soda 
in  the  cup,  A,  until  it  reaches  the  positive  platinum  pole  in  the 
cup  c,  and  consequently  it  passes  through  the  potash  without 
forming  any  permanent  compound  with  it.     This,  however,  sup- 
poses that  the  potassium  of  the  potash  also  moves  towards  the 
cup  A,  and  mingles  with  the  soda,  which  is  probably  the  ca  e, 
and  also  that  the  composition  of  sulphuric  acid  is  SO4.     The 
process  of  transfer  is  complicated,  and  will  be  more  fully  ex- 
plained hereafter,  when  we  come  to  treat  of  the  binary  theory 
of  salts. 

374.  Exception  in  the  case  of  the  production  of  insoluble 
compounds.    Chloro-hydric  and  nitric  acids  may  be,  in  the  same 
manner,  transported  through  solutions  of  strontia  and  baryta, 

373.  Describe  Sir  II.  Davy's  experiment.     How  may  this  be  explained? — 374.  State  the 
exception  iu  the  casa  of  insoluble  products.    How  may  this  be  explained  ? 


THE    SUCCESSIVE    ACTION    OF 


350 


and  reciprocally,  these  substances  passed  through  the  acids 
without  any  combination,  though  they  have  a  strong  affinity  for 
each  other;  but  if  it  be  attempted  to  pass  sulphuric  acid 
through  strontia,  or  baryta,  combination  takes  place,  and  the 
insoluble  sulphates  of  strontia  and  baryta  are  precipitated  to 
the  bottom  of  the  cup  B.  The  same  result  followed  when  this 
acid  was  placed  in  the  cup  B,  and  it  was  attempted  to  transmit 
stro;itia  and  baryta  through  it ;  insoluble  sulphates  of  these  sub- 
stances were  always  thrown  down  in  B.  The  conclusion,  there- 
fore, seems  to  be  that  this  transfer  of  acids  and  alkalies  may  take 
place  when  the  resulting  compound  is  soluble,  but  can  not  take 
place  when  the  resulting  compound  is  insoluble.  This  re>ult  is 
explained  as  in  the  two  previous  cases  by  polarization,  the  only 
difference  being  that  the  acid,  when  it  strikes  the  baryta,  in  the 
cup  B,  forming  an  in-oluble  sulphate  of  baryta,  can  no  longer 
transmit  the  current,  no  solid  substance  being  able  to  do  this, 
(see  §  366,)  and  is  immediately  precipitated  out  of  the  line  of 
voltaic  influence  to  the  bottom  of  the  vessel. 

37  J.    The  successive  action  of  the  same  current  on  different 
vessels  of  water.    In  Fig.  168,  if  1,  2,  3,  4,  be  a  row  of  glass 


1234 

Tke  action  of  one  Current  upon  different  Vessels  of  Water. 

cups  containing  acidulated  water,  and  g  h,  ef,  c  d,  a"h,  be 
slips  of  platinum,  joined  by  wires,  on  forming  the  connection 
with  the  battery,  oxygen  will  be  discharged  at  the  left  hand 
slip,  in  each  cup,  and  hydrogen  at  the  right  hand  slip,  and  in  all 
the  cups  at  the  same  instant ;  and  this  will  continue  as  long  as 
the  current  passes.  It  is  plain,  from  this,  that  there  is  a  posi- 
tive and  negative  pole  formed  in  each  cup,  and  not  simply  in 

375.  What  is  the  successive  action  of  the  current  on  the  four  vessels  of  water  shown 
in  Fiy.  138  ?  How  many  poles  are  formed  in  each  cup  ?  How  may  this  be  explained  by 
Fig.  169? 

15* 


360          THE    SAME    CURRENT    ON    DIFFERENT    VESSELS. 

the  two  extreme  cup?.  Thi*  experiment  shows,  conclusively, 
that  there  is  a  state  of  polarization  extending  through  the  en- 
tire circuit.  Thus,  in  Fig,  169,  on  the  extreme  right  may  be 

seen    a    wire   of 

Fig.  169.  platinum,    polar- 

o       H         o       ii         OH  izec*  l)V tne  action 

z  °f  the  current; 
the  connecting 
wires  are  also 
polarized,  as  well 

Uecoinposiuon  effected  by  tne  rtiMrization  of  tue  the  ^ire  COIHiect- 

Entire  Circuit.  CQ  With  the   pOSl- 

tive  pole.     As 

poon  as  the  current  passes,  the  positive  electricity  moves  towards 
the  risrht,  and  the  negative  towards  the  left,  and  in  doing  ?o, 
the  hydrogen  particles  are  necessarily  drawn  in  one  direction, 
and  the  oxygen  in  the  other,  at  the  points  where  the  wires  en  er 
each  cup.  In  all  cases  where  the  metallic  circuit  is  broken  by 
the  intervention  of  ct  liquid  conductor,  composed  of  two  ele- 
ments, two  poles  will  be  formed  at  each  break,  corresponding  in 
position  with  the  poles  at  the  extremities  of  tl  e  series,  and  with 
the  poles  of  the  battery,  and  at  each  break  decomposition  takes 
place. 

376.  The  successive  action  of  the  same  current  on  vessels 
containing  different  compound  liquids.  If  we  take  a  series  of 
four  cups,  arranged  as  before,  Fig.  1 G8,  except  that  a  piece  of 
card,  or  three  or  four  folds  of  blotting  paper,  are  placed  inside 
the  cups,  between  the  slips  of  platinum,  and  then  introduce  into 
1,  a  solution  of  iodide  of  potassium,  mixed  with  solution  of  starch, 
and  into  2,  a  strong  solution  of  chloride  of  sodium,  co^red 
blue  by  sulphate  of  indigo,  and  into  3,  a  solution  of  nitrate  of 
ammonia,  colored  blue  with  tincture  of  purple  cabbage,  and  into 
4,  a  solution  of  sulphate  of  copper,  and  finally  connect  with 
the  battery,  we  shall  have  iodine  set  free  at  the  positive  pole  in 
1,  shown  by  changing  the  starch  blue ;  chlorine  set  free  at  the 
same  pole  in  2,  shown  ty  its  bleaching  the  vegetable  blue ;  nitric 
acid  set  free  in  3,  shown  by  its  reddening  the  vegetable  blue ; 
sulphuric  acid  in  4.  On  the  other  hand,  at  the  negative  pole  in 
1,  we  shall  find  potash  ;  in  2,  soda ;  in  3,  ammonia  ;  in  4,  oxide 
of  copper.  These  different  substances  are  attracted  towards  their 
respective  poles  from  the  fact  that  they  are  themselves  possessed, 
naturally,  of  the  opposite  kind  of  electricity.  The  iodine,  chlo- 

376.  What  is  the  successive  action  of  the  same  current  on  various  compound  liquids  1 


ELECTRO-NEGATIVE    AND    POSITIVE    BODIES.  361 

rine,  nitric  acid,  and  sulphuric  ac'd,  are  naturally  charged  with 
positive  electricity,  and  the  potash,  soda,  ammonia,  and  oxide  of 
copper,  wiih  negative  electricity.  All  the  chemical  elements 
seem  to  possess  a  definite  electrical  character,  and  this  has  led 
to  their  division  into  positive  and  negative  electrics.  Those  are 
called  positive  electrics  which  appear  at  the  negative  pole  in 
any  decomposing  cell,  and  those  negative  which  appear  at  the 
positive  pole,  on  the  principle  that  oppositely  electrified  bodies 
attract  each  other. 

377.  Electro-Negative  Bodies. 

1.  Oxvgen.  8.  Selenium.  15.  Antimony. 

2.  Sulphur.  9.  Arsenic.  16.  Tellurium. 

3    Nitrogen.  10.  Chromium.  17.  Columbium. 

4.  Chlorine.  11.  Molydenum.  18.  Titanium. 

5.  Iodine.  12.  Tungsten.  19.  Silicon. 

6.  Fluorine.  13.  Boron.  20.  Osmium. 

7.  Phosphorus.  14.  Carbon.  21.  Hydrogen. 

378.  Electro-Positive  Bodies. 

1.  Potassium.  11.  Zirconitun.  21.  Bismuth. 

2.  Sodium.  12.  Manganese.  22.  Uranium. 

3.  Lithium.  13.  Zinc.  23.  Copper. 

4.  Barium.  14.  Cadmium.  24    Silver. 

5.  Strontium.  15.  Iron.  25.  Mercury. 

6.  Calcium.  16.  Nickel.  26.  Palladium. 

7.  Magnesium.  17.  Cobalt.  27.  Platinum. 

8.  Glucinium.  18.  Cerium.  28.  Rhodium. 

9.  Yttrium.  19.  Lead.  29.  Indium. 
10.  Aluminium.  20.  Tin.  30.  Gold. 

379.  The  law  of  chemical  decomposition  by  the  electrical 
current.    Mr.  Faraday  has  demonstrated  the  following  law  of 
chemical  decomposition  by  the  current.     When  the  same  cur- 
rent acts  successively  upon  a  series  -of  solutions,  as  in  Fig.  1 68, 
the  weights  of  the  elements  which  are  set  free  at  each  pole  are 
in  the  same  proportion  as  their  chemical  equivalents.     Thus,  1 
being  the  chemical  equivalent  of  hydrogen,  and  8  the  equivalent 
of  oxygen,  when  water  is  decomposed,  the  proportion  of  hydro- 
gen to  oxygen  produced,  is  always  as  1  to  8.     The  chemical 
equivalent  of  potassium  being  40,  while  that  of  oxygen  is  8,  in 
the  decomposition  of  the  oxide  of  potassium  or  potash,  the  pro- 
portion of  potassium,  by  weight,  to  the  oxygen,  is  always  as  40 
to  8.     Consequently,  when  a  current  of  electricity  is  passed 
through    a    series  of   cups,   charged   with  different  compound 
liquids,  as  in  Fig.  1G8,  the  weight  of  the  different  elements  set 
free  at  the  poles  in  each  cup,  is  not  equal,  as  might  be  supposed 
from  the  equality  of  the  force  which  acts  upon  them,  but  varies 
according  to  the  chemical  equivalent  of  the  element.     If  cup  1 

377.  What  is  meant  by  electro-negative  bodies  ?  Which  is  the  most  highly  electro-nega- 
tive body  ?— 378.  What  is  an  electro-positive  body  ?  Which  is  the  most  highly  electro- 
positive body  ? — 379.  State  Faraday's  law  of  chemical  decomposition.  Explain  this  law 
by  the  atomic  theory. 


362  THE    VOLTAMETER. 

contain  water,  cup  2  chloride  of  sodium,  cup  3  iodide  of  potas- 
sium, cup  4  chloro-hydric  acid,  while  the  weight  of  hydrogen 
set  free  in  cup  1  compared  to  that  of  oxygen,  is  as  1  to  8,  the 
weight  of  the  elements  set  free  in  cup  2  is  not  the  game, 
but  as  35.5  of  chlorine  to  23  of  sodium;  in  cup  3,  it  is  127 
of  iodine  to  40  of  potassium ;  in  cup  4,  it  is  35.5  of  chlo- 
rine to  1  of  hydrogen.  The  reason  of  this  is,  that  the  atoms 
of  the  elements  differ  in  weight  according  to  these  numbers,  and 
when  two  substances  unite,  they  do  so  atom  to  atom.  It  fol- 
lows, as  a  consequence,  that  when  these  atoms  are  separated 
from  each  other,  the  weights  of  the  elements  produced  are  always 
those  of  their  atoms ;  in  other  words,  of  their  chemical  equiva- 
lents. This  will  become  clearer  hereafter. 

380.  The  amount  of  zinc  dissolved  from  the  generating- 
plate  is  always  proportioned  to  the  amount  of  chemical  decom- 
position produced,  and  vice  versa.     Not  only  is  this  true  in 
respect  to  the  decomposition  effected  by  the  current,  after  it 
leaves  the  battery,  but  also  in  reference  to  the  chemical  action 
within  the  battery  itself.     Thus,  for  every  9  grs.  of  water,  con- 
sisting of  8  grs.  of  oxygen,  and  1  gr.  of  hydrogen,  that  are  de- 
composed by  the  electrical  current,  in  cup  1,  Fig.  168,  exactly 
32.7  grs.  of  zinc  have  united  with  8  grs.  of  oxygen,  and  been 
dissolved  in  the  acidulated  water  of  each  cup  of  the  battery. 
And  on  the  contrary,  if  32.7  grs.  of  zinc  have  been  dissolved 
in  each  cup  of  the  battery,  it  will  be  found  that  the  electrical 
current  has  decomposed  exactly  9  grs.  of  water  in  cup  1,  and 
set  free  8  grs.  of  oxygen,  and  1  gr.  of  hydrogen.     If  a  smaller 
amount  of  zinc  has  been  dissolved,  a  less  amount  of  electricity 
has  been  produced,  a  less  amount  of  acidulated  water  decom- 
posed in  the  cells,  and  a  less  amount  of  the  various  solutions  in 
the  cups  outside  of  the  battery.     The  amount  of  decomposition 
effected  becomes,  consequently,  a  measure  of  the  strength  of 
the  electrical  current.     Upon  this  principle  depends  the  action 
of  the  voltameter. 

381.  The  Voltameter.     This  is  an  instrument  invented  by 
Mr.  Faraday,  for  the  purpose  of  determining  the  voltaic  power 
of  any  circuit.     It  consists  of  an  upright  glass  cell,  having  a 
bent  tube,  c,  fitted  into  its  upper  part  by  accurate  grinding; 
Fig.  170.     This  tube  is  curved  in  such  a  way  as  to  dip  beneath 
the  edge  of  the  carefully  graduated  jar,  d,  which  is  entirely 

380.  Is  there  any  proportion  between  the  amount  of  zinc  dissolved  in  the  interior  of 
the  battery,  and  the  amount  of  chemical  decomposition  effected  outside  of  it  ?  State  the 
proportion  of  zinc  dissolved,  and  of  water  decomposed. — 381.  Describe  the  voltameter. 
JIow  may  it  be  used  to  indicate  tlie  force  of  tlie  current  ? 


ELECTRO-PLATING. 


3G3 


Tiie    Voltameter, 


170.  filled      with 

water.  With- 
in the  glass 
cell  two  plati- 
num plates  are 
arranged,  H, 
connected  with 
the  negative 
pole  of  the  bat- 
tery,  and  o, 
with  the  posi- 
tive. The  cell 
is  then  entirely 
filled  with  acid- 
i^ated  water, 

and  aho  the  bent  tube,  c.  The  instrument  is  then  connected 
with  the  battery  by  means  of  the  wires,  and  made  to  form  a 
part  of  the  circuit ;  the  acidulated  water  in  the  glass  cell  imme- 
d  ately  be^iiH  to  be  decomposed,  and  the  gases  produced  are 
conveyed  by  the  bent  tube  to  the  graduated  jar,  d,  by  which 
their  volume  is  measured.  The  volume  produced  is  in  propor- 
tion to  the  strength  of  the  current,  and  the  amount  of  zinc  dis- 
solved within  the  battery,  and  thus  this  instrument  becomes  a 
measure  of  voltaic  intensity. 

382.  Electrc-Platingr  and  Gilding-.  A  very  important  ap- 
plication is  made  of  these  facto  in  the  arts.  It  will  be  recol- 
lected that  in  all  the  cases  of  decomposition  of  metallic  solu- 
tions mentioned  above,  the  oxide  of  the  metal  is  deposited 
around  the  negative  pole,  the  acid  at  the  positive  pole.  If,  then, 
any  metallic  article  be  attached  to  the  negative  wire  of  the  bat- 
tery, it  becomes  in  effect  the  pole  of  the  battery,  and  might  be 
expected  to  benome  coated  with  the  metallic  oxide  in  question; 
and  so  it  would  be,  if  it  were  not,  that  at  the  same  time,  with 
the  metallic  salt,  a  small  portion  of  the  water  is  also  decomposed, 
an  1  its  hydrogen  appearing  at  the  negative  pole  at  the  same 
moment  with  the  metallic  oxide,  decomposes  it,  unites  with  the 
oxygen  to  form  water,  and  sets  the  metal  free,  as  in  the  case 
o  '  rli-.i  cooper ;  see  Fig.  1 G6.  The  article  attached  to  the  negative 
pola  consequently  becomes  coated  with  a  covering  of  metal,  in- 
stea  1  of  a  metall  c  oxide.  The  nature  of  the  metal  deposited 
will  depend  upon  the  metallic  solution  employed.  If  it  be  a 


332.  State  the  principle  of  electro-plating  arid  gilding. 


364 


ELECTROTYPING. 


solution  of  silver,  the  article  attached  to  the  negative  pole  will 
become  coated  with  silver;  if  it  be  a  solution  of  gold,  with 
gold ;  if  it  be  copper,  with  copper.  It  is  evident,  also,  that 
while  hydrogen  is  set  free  at  the  negative  pole,  a  corresponding 
amount  of  oxygen  must  escape  from  the  positive  pole. 

383.  Electrotyping-.  In  order,  therefore,  to  coat  or  gild  sub- 
stances which  are  good  conductors  of  electricity,  with  any  metal, 
it  is  only  neces?ary  to  attach  them  to  the  negative  pole  of  a  bat- 
tery in  full  operation,  and  place  them  in  a  solution  of  the  metal 
desired,  the  positive  pole  being  introduced  into  the  same  solu- 
tion, at  a  little  distance  from  it.  A  small  battery  is  quite  suffi- 
cient, and  in  general  one  cup  of  Bunsen's  arrangement  will 
answer  for  all  common  purposes.  The  process  is  fully  repre- 
sented in  Fig.  171,  where  o  is  the  battery;  c  is  the  vessel  con- 
Fig.  171. 


Electro -Plating. 

taming  the  metallic  solution,  which  in  this  case  is  the  sulphate 
of  copper ;  D  is  a  metallic  rod  connected  with  the  positive  pole, 
and  having  a  plate  of  copper  suspended  from  it,  and  dipping 
into  the  liquid ;  B  is  another  metallic  rod,  connected  with  the 
negative  pole  of  the  battery,  from  which  the  articles  to  be  cov- 
ered with  copper  are  suspended.  Thus,  these  articles  are  ma^e 
the  negative  pole  of  the  'battery,  and  the  copper  plate  suspended 
from  D  becomes  the  positive  pole.  The  connections  being 
formed,  the  sulphate  of  copper  is  decomposed  into  sulphuric 
acid  and  the  oxide  of  copper ;  at  the  same  time,  a  portion  of 
the  water  of  the  solution  is  decomposed  into  oxygen  and  hydro- 
gen. The  sulphuric  acid  and  the  oxygen  are  drawn  towards 

'    383.  Describe  the  electrotype  process. 


THE    PROTECTION    OP  365 

the  positive  pole,  which  is  the  copper  plate  suspended  from  D, 
and  the  oxygen  immediately  uniting  with  it  to  form  the  oxide 
of  copper,  this  is  immediately  taken  up  by  the  sulphuric  acid, 
converted  into  the  sulphate  of  copper,  and  then  dissolved  in  the 
solution,  so  that  just  as  much  copper  is  thus  restored  to  the  solu- 
tion as  is  taken  from  it  by  the  action  of  the  current ; .  and  its 
strength  sustained  for  an  indefinite  period.  On  the  other  hand, 
the  oxide  of  copper,  and  hydrogen,  are  drawn  towards  the  nega- 
tive pole,  which  is  the  article,  or  articles,  suspended  from  the 
rod  B,  and  here  the  hydrogen  uniting  with  the  oxygen  of  the 
oxide  to  form  water,  the  metallic  copper  is  deposited.  In  this 
m:inner,  exact  copies  may  be  made  of  all  metallic  articles.  If 
the  article  be  a  copper  medal,  and  it  be  desired  to  get  an  exact 
copy  of  it,  every  part,  except  the  face,  to  be  copied,  is  covered 
with  wax,  and  it  is  then  suspended  from  the  rod  B,  in  the  sul- 
phate of  copper  solution ;  it  thus  becomes  completely  covered 
with  metallic  copper  upon  the  exposed  surface ;  the  thickness 
of  the  deposit  will  depend  upon  the  duration  of  immersion. 
On  removal  from  the  solution,  the  deposited  copper  will  tightly 
adhere  to  the  original  metal,  but  it  may  be  separated  from  it  by 
gently  heating  with  a  spirit  lamp.  The  cast  thus  formed  is  the 
reverse  of  the  medal,  and  if  it  be  desired  to  obtain  a  copy  in 
relief,  it  is  only  necessary  to  subject  the  cast  to  the  same  pro- 
cess, by  attaching  it  to  tho  negative  pole  of  the  battery,  and 
immersing  it  in  a  solution  of  sulphate  of  copper.  In  this  man- 
ner, faithful  copies  may  be  made  of  all  metallic  articles,  by  de- 
positing metals  upon  them.  The  finest  line  engravings  may  be 
accurately  reproduced.  All  the  copper  plates  of  the  coast  sur- 
vey are  formed  by  this  process ;  the  originals  are  never  used, 
but  only  the  copies,  and  any  required  number  of  these  may 
be  produced  at  a  small  expense.  When  the  articles  to  be  cov- 
ered are  not  metallic,  it  is  necessary  to  cover  them  with  a 
fine  powder  which  is  a  good  conductor  of  electricity,  and  then 
treat  them  in  the  usual  manner.  The  substance  most  commonly 
used  for  this  purpose  is  plumbago,  in  very  fine  powder.  The 
ele-trotype  plates  from  which  books  are  printed,  are  made  by 
taking  an  impression  in  wax,  of  the  original  types ;  covering 
this  plate  of  wax  with  a  coating  of  plumbago,  and  immersing  it 
in  a  solution  of  sulphate  of  copper,  wkh  an  attachment  to  the 
negative  pole  of  a  battery.  Oa  the  po  itive  pole  a  large  plate 
of  copper  is  suspended,  which  is  gradually  dissolved  at  the  same 
rate  as  the  copper  is  deposited  upon  the  wax,  and  the  strength 
of  the  solution  is  thus  maintained,  until  the  whole  plate  has 


366  COPPER   SHEATHING/ 

disappeared.  The  powdered  wax  receives  a  deposit  of  copper 
upon  the  whole  of  its  surface,  "and  in  its  finest  lines,  which 
gradually  increases  in  thickness  until  it  is  strong  enough  to  be 
separated  fvom  the  wax,  mounted  upon  wood  or  metal,  and  used 
for  printing.  The  wax  may  be  melted  into  a  new  sheet,  and 
applied  .to  another  portion  of  types.  This  is  by  no  means  the 
only  application  in  the  arts.  Gilding,  silvering,  bronzing,  may 
all  be  accomplished  by  it,  and  it  has  grown  to  be  a  very  impor- 
tant branch  of  industry. 

334.  The  protection  of  the  copper  sheathing-  of  Ships-  By 
an  ingenious  application  of  the  same  principles  the  metals  can 
be  protected  from  the  action  of  corrosive  liquids  in  which  they 
may  be  immersed.  Thus,  a  zinc  plate,  placed  in  dilute  sulphu- 
ric acid,  will  decompose  the  water  with  great  rapidity,  and  itself 
be  quickly  oxidated,  and  finally  dissolved.  If,  however,  the 
plate  of  zinc  be  attached  to  the  negative  pole  of  a  battery,  and 
thus  rendered  negatively  electric,  at  the  same  time  that  a  slip 
of  platinum,  attached  to  the  positive  pole,  is  placed  in  the  liquid 
immediately  opposite,  it  will  not  decompose  the  water,  will  suf- 
fer no  oxidation,  and  remain  undissolved.  The  reason  is,  be- 
cause the  oxygen  of  the  water  is  itself  a  negative  electric,  and 
therefore  repelled  from  the  negative  zinc ;  for  the  same  reason 
the  acid  is  also  repelled.  In  like  manner,  copper  will  rapidly 
decompose  chloro-hydric  acid,  forming  chloride  of  copper,  and 
finally  be  itself  wholly  dissolved ;  but  if  the  copper  be  rendered 
negatively  electric,  it  will  remain  unaffected  by  the  acid,  because 
chlorine  is  also  a  negative  electric,  and  is  repelled  from  a  body 
which  is  charged  with  electricity  of  the  same  kind.  In  this 
way  it  is  possible  to  protect  metals  by  means  of  galvanic  ar- 
rangements from  the  influence  of  the  most  corrosive  liquids. 
Sir  H.  Davy  made  an  ingenious  application  of  this  principle  to 
the  protection  of  the  copper  sheathing  of  ships  from  the  action 
of  eea  water.  Sea  water  contains  in  solution  a  variety  of  metal- 
lic salt?,  the  most  important  of  which  is  chloride  of  sodium,  or 
common  salt.  The  chlorine  contained  in  this  substance  has  a 
very  strong  affinity  for  copper,  and  will  attack  it  with  great  vio- 
lence, forming  a  green  chloride  of  copper,  which  is  at  once  dis- 
solved by  the  water,  and  thus  the  copper  is  rapidly  wasted. 
Chlorine,  however,  is  an  electro-negative  substance,  and  if  the 
copper  sheathing  could  be  rendered  also  electro-negative,  it 

384.  How  may  the  metals  be  prevented  from  corrosion  by  the  action  of  the  electro- 
negative elements,  such  as  oxygen,  and  chlorine?  On  this  principle,  how  may  the  copper 
sheathing  of  ships  be  protected  1  What  disadvantages  have  arisen  from  this  protection  ? 


MAGNETIC  EFFECTS  OF  THE  CURRENT.        367 

r 

would  be  repelled,  instead  ot  attracted,  and  the  metal  would  ba 
perfectly  protected  from  corrosion.  This  can  b3  done  by  driv- 
ing zinc  nails  into  the  copper,  at  proper  intervals.  The  zinc  at 
once  becomes  electro-positive,  attracts  the  chlorine  to  itself,  and 
sets  01*  foot  an  electrical  current,  which  is  transferred  to  the 
copper ;  it  thus  becomes  the  generating  plate  of  a  battery,  while 
the  copper  becomes  the  conducting  plate.  The  copper  is  thus 
made  electro-negative,  and  tends  as  strongly  to  repel  the  chlo- 
rine as  the  zinc  does  to  attract  it.  By  this  arrangement,  copper 
sheathing  is  completely  protected,  and  kept  entirely  free  from 
corrosion ;  but  unfortunately,  at  the  same  time  that  the  chlorine 
is  repelled,  other  substances,  such  as  lime  and  magnesia,  being 
electro-positive  in  their  character,  are  attracted  to  the  copper. 
This  earthy  coating  furnishes  good  points  of  attachment  to  sea 
weeds  and  shell  fish,  which  soon  make  the  bottom  of  ships  very 
foul,  and  greatly  impade  their  progress,  It  has  become  neces- 
sary, therefore,  to  discard  the  invention,  and  the  same  end  is  now 
partially  attained  by  the  use  of  a  kind  of  brass  sheathing,  com- 
posed of  zinc  and  copper,  and  called  Muntz's  yellow  metal.  On 
the  same  principle,  metallic  structures,  such  tts  iron  pillars,  fen- 
ces, and  the  like,  ni£y  be  protected  from  atmospheric  action  by 
the  insertion  of  small  bits  ot  zinc,  at  regular  intervals.  There 
are  other  applications  of  the  same  principles  possessed  of  nearly 
equal  interest, 


III, 


Magnetic  effects  of  the  Current.  The  power  of  light- 
ning in  destroying  and  reversing  the  poles  of  a  magnet,  and  in. 
imparting  magnetic  properties  to  pieces  of  iron  which  did  not 
previously  possess  them,  has  been  known  for  a  long  period,  and 
led  to  the  opinion  that  similar  effects  might  be  produced  by  the 
common  electrical  machine,  and  the  galvanic  battery.  No  re- 
sults of  importance  were  obtained,  however,  until  the  year 
1819.  In  the  winter  of  that  year  Professor  Oersted,  of  Copen- 
hageri;  discovered  that  if  a  magnetic  needle  be  brought  near  a 
copper  wire,  connecting  the  two  poles  of  a  battery,  and  through 
which  the  electrical  current  is  passing,  the  needle  is  at  once 
violently  agitated,  deflected  from  its  position,  and  made  to  as- 

385.  What  effect  is  produced  upon  the  magnetic  needle  by  a  wire  carrying  the  current, 
placed  parallel  to,  and  above,  it  ? 


368 


THE    MAGNETIC    NEEDLE    DEFLECTED. 


S  ^  ,. 


sume  a  position  at  right  angles  to  the  wire.  Thus,  if  the  wire 
be  placed  upon  the  magnetic  meridian,  pointing  north  and  south, 
the  north  end  connected  with  the  negative  pole  or  zinc  plate  of 
the  battery,  and  the  south  end  connected  with  the  positive  pole, 
or  the  platinum  plate  of  the  battery,  and  the  magnetic  needle 
be  placed  below  the  wire,  it  will  at  once  assume  a  position  at 
right  angles  to  the  wire,  the  north  pole  moving  to  the  west,  and 
the  south  pole,  to  the  east,  as  represented  in  Fig.  172.  If  the 

needle    be    placed    above 

Fl"*  172<  the  wire,  the   north  pole 

will  move  to  the  east,  and 
the  south  pole  to  the  west. 
When  the  needle  is 
placed  in  the  same  hori- 
zontal plane  with  the  wire, 
it  attempts  to  assume  a 
vertical  position,  the  north 
pole  dipping  when  the 
wire  is  to  the  west  of  it, 
and  rising  when  the  wire 
is  to  the  east  of  it.  If 
the  current  be  reversed, 
by  changing  the  connec- 
tions with  the  battery,  and  be  made  to  pass  from  north  to  south, 
instead  of  from  south  to  north,  the  movements  of  the  needle 
are  all  reversed.  The  explanation  given  of  these  movements  is, 
that  two  magnetic  forces  are  generated  by  the  passage  of  the 
current,  circulating  around  the  wire  in  opposite  directions,  along 
its  whole  extent,  and  at  right  angles  to  it ;  the  tendency  of  one 
force  is  to  cause  the  north  pole  of  the  needle  to  revolve  around 
the  wire  in  one  direction ;  the  tendency  of  the  other  is  to  cauee 
the  south  pole  to  revolve  in  like  manner  in  the  opposite  direction  ; 
the  magnet,  consequently,  comes  to  rest  in  a  position  of  equilib- 
rium between  these  two  forces,  directly  across  the  wire.  Besides 
this  directive  action  upon  the  magnet,  the  conducting  wire  also 
exerts  an  attractive  action,  as  may  be  shown  by  suspending  a 
magnetized  sewing  needle  from  a  silk  thread,  and  causing  an 
electrical  current  to  pass  in  an  horizontal  direction  by  the  side 
of,  and  very  near  it.  It  also  exerts  an  inductive-magnetic  action, 
by  which  soft  iron  wires,  or  bars,  placed  across  the  conducting 
wire  at  right  angles,  are  rendered  magnetic  as  long  as  the  cur- 

By  a  wire  placed  below  the  needle  ?  If  t'.ie  current  be  reversed,  what  is  the  effect 
upon  the  needle ?  Whr.t  i.*  t"ie  explanation  given  of  these  movements?  What  other 
magnetic  elfects  are  produced  by  the  current? 


Effects  of  Galvanic  E'frtricity  on  the  Magnetic 

Needle. 


THE    MAGNET    DESCRIBED.  369 

r 

rent  circulates.  The  action  of  the  conducting  wire  is,  there- 
fore, threefold. 

336.  What  is  a  X&ag-net?  A  magnet  is  a  body  which 
possesses  the  power  of  attracting  masses  of  iron,  and  a  few 
other  metallic  substances,  such  as  nickel,  cobalt,  and  chromium. 
They  are  distinguished  into  natural  and  artificial.  The  natural 
magnet  is  an  oxide  of  iron,  first  found  in  Magnesia,  a  district 
of  Asia  Minor,  and  from  this  has  received  its  name.  Artificial 
magnets  are  bars,  or  needles,  of  tempered  steel,  which  do  not 
naturally  possess  the  properties  of  a  magnet,  but  have  acquired 
them  by  friction  with  another  magnet,  by  the  action  of  electri- 
city, or  by  percussion  in  the  magnetic  meridian.  They  are 
more  powerful  than  natural  magnets,  and  possess  identical  prop- 
erties. The  attractive  power  of  magnets  is  exercised  at  all  dis- 
tances, and  through  all  bodies,  but  decreases  with  the  distance, 
and  varies  with  temperature ;  at  a  red  heat,  magnets  lose  their 
attractive  power  altogether. 

387.  The  poles  of  the  Mag-net.    The  attractive  force  of  the 
magnet  does  not  reside  equally  at  all  points  upon  its  surface ; 
this  may  be  clearly  shown  by  holding  a  magnet  immediately 
over  iron  filings  placed  upon  a  sheet  of  paper,  when  the  filings 
will  be  seen  to  accumulate  equally  at  the  ends  of  the  bar,  while 
they  will  not  be  attracted  at  all  at  the  middle ;  Fig.  173.     These 

two    ends,   at 

FiS-  i^3-  which     the 

force  resides, 
are  called  the 
poles  of  the 
magnet.  Eve- 
ry  magnet 

The  Magnet.  pOSSCSSCS    two 

poles,  as    one 

can  not  exist  without  the  other.  If  a  magnet  be  suspended 
upon  a  pivot,  it  will  place  itself  very  nearly  upon  a  meridian 
line,  and  one  pole  will  invariably  point  towards  the  north,  and  the 
other  towards  the  south ;  if  it  be  moved  from  this  position,  in  a 
few  moments  it  will  resume  it,  the  same  pole  pointing  to  the 
north  as  before ;  hence  one  pole  of  the  magnet  is  called  the 
north,  and  the  other  the  south  pole. 

388.  The  mutual  action  of  the  Poles.    The  two  poles  at- 

335.  What  is  a  magnet  ?  What  is  the  origin  of  the  name  ?  What  are  artificial  mag- 
nets ?  What  is  the  effect  of  a,  red  heat  on  a  magnet  ? — 387.  Does  the  attractive  force  of 
the  magnet  reside  equally  at  all  points  on  its  surface  ?  What  are  the  poles  of  the  mag- 
net ? — 388.  State  the  difference  betwa3a  the  polar  forces  of  the  magnet. 


370 


THE    DIRECTIVE    ACTION    OF    THE    EARTH. 


174, 


tract  iron  filings  equally,  and  appear  to  be  identical  in  tliefr 
character;  but  in  fact  they  possess  different  kinds  of  magnetism, 
endowed  with  properties  opposite,  but  analogous  to  each  other. 
Thus,  if  a  small  magnetic  needle,  Fig.  174,  be  suspended  from 

a  fine  thread,  and  the 
north  pole  of  a  second 
needle  be  presented  to 
the  north  pole  of  the  first, 
a  quick  repulsion  takes 
place ;  but  if  the  same 
north  pole  be  presented 
to  the  south  pole  of  the 
suspended  needle,  attrac- 
tion immediately  takes 
place.  The  poles,  n  and 
s,  are  not  then  identical, 
since  one  is  repelled,  and 
the  other  attracted,  by 
the  same  pole,  N,  of  the 
magnet  held  in  the  hand. 
If  the  south  pole  of  the 
second  magnet  be  in  turn 
presenled  to  the  north 
pole  of  the  first,  attraction 
will  take  place ;  and  on  the  other  hand,  if  presented  to  the 
south  pole  of  the  first,  repulsion  will  ensue.  Consequently,  we 
deduce  this  principle,  that  magnetic  forces  of  the  same  kind 
repel,  and  those  of  different  kinds  attract,  each  other,  These 
t\vo  magnetic  forces  are  always  developed  at  the  same  time ; 
one  can  not  be  produced  without  the  other ;  they  are  equal  in 
amount,  are  opposite  in  their  tendencies,  and  are  capable  of 
exactly  neutralizing  each  other.  Forces  which  exhibit  this 
combination  of  equal  and  opposite  powers  are  called  polar  forces. 
Electricity  is  also  a  polar  force,  and  the  analogy  between  it  and 
magnetism,  is  so  complete  that  it  is  obvious  they  must  be  closely 
connected. 

389.  The  directive  action  of  the  Earth  upon  Mag-nets.  It 
has  been  stated  that  if  a  magnetic  needle  be  suspended  by  a 
thread,  or  supported  upon  a  pivot,  on  which  it  can  readily  turn, 
it  will  oscillate  for  a  time,  and  finally  take  a  position  nearly 
n<  rth  and  south.  If  the  needle  be  placed  upon  a  cork,  in  a 


Mutual  action  of  Magnetic  Poles. 


"".'ha-t  prinfinle  do  we  deduce  from  these  facts ?    What  are  polar  forces? — 389.  What 
is  tae  eflect  of  tae  earth  upou u  magnetic  needle? 


THE    ASTATIC    NEEDLE. 


371 


s. 


The  directive  action  of  the  Earth. 


vessel  of  water,  the  same  thing  takes  place ;  it  assumes  a  posi- 
tion north  and  south,  but  does  not  advance  either  to  the  north 
or  south.  The  action  of  the  poles  of  the  eurth  upon  the  mag- 
net is  not  attractive,  but  directive,  as  though  these  poles  were 

situated  at  an  immense  distance. 
Fig-  ITS-  The  earth  appears  to  be  a  vast 

$  magnet,  whose  poles  are  situated 
near  the  poles  of  the  earth,  the 
north  magnetic  pole  being  within 
the  arctic,  and  the  south  mag- 
netic pole  within  the  antarctic 
circle.  Consequently,  as  mag- 
netic poles  of  the  same  kind  re- 
pel, and  of  different  kinds  attract, 
each  other,  the  pole  of  an  artifi- 
cial magnet  which  points  towards 
the  north  pole  of  the  earth  must 
be  its  true  south  pole,  and  the 
pole  which  points  towards  the 
south  pole  of  the  earth  its  true 
north  pole.  Fig.  175. 

390.  The  Astatic  Needle.  The  astatic  needle  is  a  magnetic 
needle,  arranged  in  such  a  manner  that  it  is  no  longer  under  the 
directive  influence  of  the  magnetic  poles  of  the  earth,  and  con- 
sequently, will  remain  fixed  in  any  position  in  which  it  may  be 
placed,  without  tending  to  point  north  and  south.  Two  mag- 
netic needles  are  placed,  one  beneath  the  other,  and  fastened 
firmly  together  by  a  pin,  with  their  poles  reversed,  i.  e.,  the 
north  pole  of  the  upper  needle  having  the 
south  pole  of  the  lower  needle  directly  be- 
neath it,  and  the  south  pole  of  the  upper  nee- 
dle having  the  north  pole  of  the  lower  ar- 
ranged likewise.  Consequently,  the  attraction 
which  the  north  pole  of  the  earth  exerts  upon 
the  upper  needle  is  counteracted  by  the  repul- 
sion which  it  exerts  upon  the  south  pole  of 
the  needle  fixed  beneath  it;  the  compound 
needle  is  therefore  not  drawn  towards  the 
north ;  for  the  same  reason,  it  is  not  drawn 
The  Astatic  Needle.  towards  the  south,  but  remains  indifferently  in 
any  position  in  which  it  is  placed,  without  at 

la  the  aetion  attmrtivp,  or  directive  ?    What  is  the  true  north  pole  of  the  needle  ?    Tli« 
true  south  pole?— 390    Describe  the  astatic  needle. 


iff.  176. 


372  THE    INDUCTION    OF    MAGNETISM. 

the  same  time  losing  any  portion  of  its  magnetic  power ;  hence 
its  name,  derived  from  the  Greek,  which  means  unsteady,  havii  g 
no  directive  tendency. 

391.  Induction  of  XVZagnetism.  A  powerful  magnet  has  the 
power  of  inducing  magnetism  in  magnetizable  substances  placed 
near  it,  in  the  same  way  as  a  highly  charged  electrified  body 
has  the  power  of  inducing  electricity  in  all  bodies  in  its  vicin- 
ity. Thus,  if  a  piece  of  iron  be  brought  near  the  north  pole  of 
a  powerful  magnet,  but  not  touching  it,  the  end  of  the  iron 
nearest  the  magnet  will  be  affected  with  the  opposite,  and  the 
remote  end  with  the  same,  magnetism ;  consequently,  the  iron 
being  thrown  into  the  opposite  magnetic  state,  will  be  attracted 
towards  the  magnet.  This  is  the  cause  of  all  magnetic  attrac- 
tion, and  is  due  to  the  magnetism  induced  in  the  body  attracted  ; 
in  the  ca«e  of  iron  filings,  each  particle  becomes  magnetized. 
If,  while  the  piece  of  iron  is  under  the  inductive  influence  of 
the  magnet,  another  piece  of  iron  be  presented  to  it,  and  to  this 
another,  these  pieces  will  all  be  magnetized  by  induction,  with 
their  poles  reversed,  and  be  attracted  by  the  first  piece ;  Fig. 
177.  If  the  magnet  be  removed,  the  induced  magnetism  of  all 

Fisr.  177.  i 


Induction  of  Magnetism, 

the  pieces  of  iron  is  destroyed,  and  they  will  fall  to  the  ground  ; 
this  induction  is  not  prevented  by  the  interposition  of  unmag- 
netizable  substances  between  the  magnet  and  the  iron ;  a  piece 
of  glass  inserted  between  them  will  not  interfere  with  the  effect. 
392.  All  substances  are  either  attracted  or  repelled  by  the 
Magnet.— Magnetic  and  Dia- magnetic  Bodies.  It  was  formerly 
supposed  that  iron  was  the  only  substance  susceptible  of  attrac- 
tion by  the  magnet ;  it  was  afterwards  proved  that  the  metals, 
nickel  and  cobalt,  are  also  possessed  of  the  same  susceptibility, 
and  more  recently  it  has  been  discovered  that  all  bodies  are 

391.  What  is  meant  hy  the  induction  -of  magnetism?  How  can  it  be  proved?— 392. 
What  is  the  difference  between  magnetic  and  diamagnetic  bodies  ?  What  other  metals, 
besides  iron,  are  susceptible  of  magnetization  ? 


MAGNETIC    AND    DIA-MAGNETIC    BODIES. 


373 


Fig.  178. 


Tlie  Mtigiuiic  Field. 


Fig.  179. 


affected  by  the  magnet,  in  some  degree,  and  either  attracted  or 
repelled  by  it.  Thus,  if,  in  Fig.  178,  N  and  s  represent  the 
poles  of  a  powerful  horse-shoe  magnet, 
upon  which  the  observer  is  looking  down  ; 
the  line  A,  x,  connecting  the  two  poles,  may 
be  called  the  axis  of  the  magnetic  field, 
and  E,  Q,  which  crosses  it  at  right  angles, 
its  equator.  If  an  iron  needle  be  sus- 
pended by  its  centre,  above  such  a  magnet, 
it  will  take  a  horizontal  direction,  parallel 
to  the  axis  A  x,  and  is  sail  to  point  axially. 
But  if  a  stick  of  phosphorus  be  suspended 
between  the  two  poles  of  the  magnet,  it 
will  take  the  equatorial  position, 
E  Q,  the  phosphorus  being  re- 
pelled by  each  pole  to  the  great- 
est possible  distance ;  consequent- 
ly, phosphorus  is  called  a  dia-mag- 
netlc  body.  Some  of  the  metals, 
such  as  antimony  and  bismuth, 
exhibit  this  dia-magnetic  property 
in  a  still  higher  degree.  It  is  even 
possessed  by  many  substances  of 
an  organic  nature.  In  Fig.  179, 
is  represented  a  bar  of  copper, 
occupying  the  equatorial  position 
between  the  two  poles  of  an  elec- 
tro-magnet, which  project  upwards 
through  apertures  made  in  the 
table.  While  iron  is  the  most 
highly  magnetic  of  all  substances, 
there  are  many  others  not  usu- 
ally esteemed  magnetic,  which  will 
take  the  axial  position,  if  brought 
near  the  poles  of  a  powerful  magnet,  such  as  the  red  oxide  of 
iron,  and  even  a  sheet  of  writing  paper,  if  rolled  into  the  form 
of  a  short  cylinder,  .will  usually,  owing  to  the  iron  or  cobalt 
which  it  contains,  assume  a  similar  direction. 

333.    The  dia-mag-nctisan  of  Gases.     The  property  of  dia- 
magnetiam  is  not  confined  to  solids  and  liquids ;  the  gases  also 

What  is  the  axis  and  the  equator  of  the  magnetic  field?  IIo\v  can  diamagnetism  be 
illustrated  by  phosphorus  and  bismuth?  By  a  sheet  of  writing  paper?— 393.  How  can 
the  magnetism  and  diamaguetism  of  gases  be  shown? 


The  Dia-magnetism  of  Solids. 


374  OXYGEN    MAGNETIC. 

F[g-  18°-  possess  it.     Thus,  if  three  tubes  he 

arranged  in  the  equator  of  the  mag- 
netic field,  as  shown  in  Fig.  180, 
and  in  each  tube  a  piece  of  paper, 
moistened  with  chloro-hydric  acid, 
be  suspended,  and  another  piece  of 
paper,  moistened  with  ammonia,  be 
placed  in  a  bent  tube,  conveying 

'The  D'ta-magnetism  of  Gases.  the  gas  ill  question,  tllC  gas  Will  l)C- 

come  charged  with  ammoiracal  va- 
por, and  as  long  as  the  electro-magnet  is  not  brought  into  action, 
will  pass  directly  up  the  centre  tube  ;  but  as  soon  as  the  electro- 
magnet is  in  operation,  those  gases  which  are  dia-magnetic  will 
no  longer  pass  up  the  centre  tube  alone,  but  will  enter  the  side 
tubes,  arranged  in  the  equator  of  the  instrument,  and  their  pres- 
ence will  be  made  manifest  in  each  tube  by  the  white  cloud 
which  is  always  produced  when  the  fumes  of  ammonia  come 
into  contact  with  those  of  chloro-hydric  acid.  The  same  fact 
can  also  be  determined  by  blowing  eoap  bubbles  with  the  gas  in 
question,  and  bringing  them  near  the  poles  of  the  magnet ;  if 
attracted,  the  gas  is  magnetic ;  if  repelled,  it  is  dia-magnetic. 

394.  Oxygen  a  magnetic  substance.  By  suspending  a 
feebly  magnetic  glass  tube  between  the  magnetic  poles,  success- 
ively in  oxygen  and  in  vacuo,  it  has  been  found  that  it  is  le^s 
strongly  attracted  in  oxygen  than  in  the  exhausted  receiver,  and 
on  varying  the  experiment  in  different  way-,  it  has  been  proved 
that  oxygen  is  a  decidedly  magnetic  body.  A  cubic  French 
metre  of  oxygen,  which  is  rather  more  than  an  English  cubic 
yard,  and  which  ordinarily  weighs  22015  grs.,  if  it  were  con- 
densed until  it  had  a  specific  gravity  equal  to  that  of  iron,  would 
act  upon  a  magnetic  needle  with  a  force  equal  to  that  of  a  little 
cube  of  iron  weighing  8^  grs.,  and  the  magnetism  of  oxygen  is 
to  that  of  iron,  as  1 :  2647.  The  magnetic  effect  of  the  oxygen 
in  the  air  is  equal  to  that  of  a  shell  of  metallic  iron  ^\-^  of  an 
inch  in  thickness,  surrounding  the  entire  globe.  Oxygen  loses 
its  magnetism  when  strongly  heated,  and  recovers  it  agarn  when 
the  temperature  falls.  The  diminution  of  its  magnetic  intensity 
as  temperature  rises,  has  been  thought  to  explain  the  diurnal 
,  variations  of  the  needle.  It  has  also  been  ascertained  that  the 
j  . , 

894  How  can  the  magnetism  of  oxygen  be  proved  ?  To  what  is  this  magnetic  power 
equal  when  compared  wit1!  that  of  iron?  What  is  the  effect  of  heat  upon  it?  is  the 
flame  of  candles  and  the  electric  light  magnetic,  or  dia-magnetic' 


EFFECT  OF  CURRENT  ON  THE  MAGNETIC  NEEDLE.   375 

flame  of  candles,  and  of  the  electric  light,  is  dia-magnetic  when 
placed  between  the  poles  of  a  powerful  imignet. 

395.  Magnetic  and  Dia-magnetic  Bodies.  The  following 
is  a  list  of  various  substances  arranged  in  the  order  of  their 
magnetic  and  dia-magnetic  powers  as  determined  by  Mr.  Fara- 
day. 


Magnetic. 
Iron. 
Nickel. 
Cobalt. 
Manganese. 
Chromium. 
Cerium. 
Titanium. 
Palladium. 
Crown  Glass. 
Platinum. 
Osmium. 
Oxygen. 


Dia-magnetic. 

Bismuth.  Copper. 

Phosphorus.  Water. 

Antimony.  Gold. 

Zinc.  Alcohol. 

Silico-borate  of  Lead.  Ether. 

Tin.  Arsenic. 

Cadmium.  Uranium. 

Sodium.  Rhodium. 

Flint  Glass.  Iridium. 

Mercury.  Tungsten. 

Lead.  Nitrogen. 
Silver. 


395.  Reason  why  a  Xffag-netic  Needle  assumes  a  position 
at  right  angles  to  the  Conducting:  Wire.  From  what  has  been 
said,  it  is  evident  that  the  magnetic  needle  assumes  a  position  at 
right  angle.i  to  the  wire  connecting  the  two  poles  of  the  battery, 
because,  of  the  creation  of  two  magnetic  forces  circulating  around 
the  wire  in  opposite  directions,  and  at  right  angles  to  its  length ; 
the  north  pole  of  the  needle  being  controlled  exclusively  by  the 
south  magnetic  force,  and  the  south  pole  exclusively  by  the  north 
magnetic  force.  A  galvanic  current  can  not  traverse  a  wire  with- 
out generating  polar  magnetic  forces,  circulating  around  it  at  right 
angles  along  its  entire  length.  Thus,  in  Fig.  181,  if  A,  B,  rep- 
resent a  wire,  through  which 

Fi--  1P1-  an  electrical  current  is  passing, 

indicated  by  the  dart,  the  small 
arrows  indicate  one  of  the  mag- 
netic forces,  or  magnetic  cur- 

Iralvantc  Current  mcii'tating  Magnetic  -. 

Force.  rents,  as  they  are  sometimes 

called,  which  cross  it  at  right 

angles,  and  the  galvanic  current  can  not  be  made  to  traverse  such 
a  wire  without  producing  these  magnetic  forces.  Not  only  does 
the  electrical  current  generate  these  polar  magnetic  forces  which 
cross  it  at  right  angles  to  its  length,  but  it  also  magnetizes  the  wire 
itself.  This  may  be  proved  by  the  attraction  which  it  exerts 
upon  iron  filings  wh  n  they  are  brought  near  it ;  if  the  current 
be  broken,  the  filings  immediately  fall.  These  fiT.ngs  are  at- 

83">.  Mention  some  of  fie  principal  magnetic  and  diamagnetic  bodies. — 393.  What  is 
the  reason  that  the  conducting  wire  affect.-?  the  magnetic  needle?  Does  the  wire  itself 
become  magnetic?  How  can  t.iis  be  proved?  Is  it  possible  for  the  current  to  traverse 
a  wire  without  producing  magnetism  ? 

16 


376  ELECTRO-MAGNETS. 

* 

traded  to  the  wire  by  the  magnetism  which  it  induces,  and  as 
long  as  they  are  under  its  influence  they  are  made  temjorary 
magnets,  in  the  same  way  as  they  would  be,  if  acted  upon  by 
a  powerful  permanent  magnet.  See  §  3(J1. 

397.  The  galvanic  current  induces  Magnetism.— Electro- 
magnets. ISTot  only  are  iron  filings  thus  induttive'y  con- 
verted into  temporary  magnets  by  the  wire,  but  larger  pieces 
of  iron,  if  brought  near  the  wire,  are  similarly  afiechd. 
If  a  small  rod  of  iron  be  placed  at  right  angles  across  the 
connecting  wire,  it  will  become  strongly  magnetic,  ar.d  con- 
tinue so,  as  long  as  the  electrical  current  passes  ;  if  the  connec- 
tion of  the  wire  with  the  ba'tery  be  broken,  the  magneti.-m 
ceases.  If  the  rod  be  placed  in  a  small  glass  tube,  and  the 
conducting  wire,  instead  of  crossing  once  at  right  argles,  be 
carried  around  it  several  times,  forming  a  spiral  coil,  so  that  the 
electrical  current  is  made  to  pass  several  times  around  the  iron 
rod,  its  magnetic  power  will  be  greatly  increased..  The  extremi- 
ties of  the  rod  will  be  the  poles  of  the  temporary  magnet,  and 

this  wi.l  be   the  ca?e 

Fig.  182.  even  if  the  extremities 

of  the  iron  rod  project 
some  distance  beyond 

Right  Hand  Helix.         n  the  coil.     Such  a  spiral 

coil  of  wire  is  called  a 
helix,  and  when  wound  to  the  right,  constitutes  a  right-handed 
helix,  Fig.  182  ;  and  when  to  the  left,  a  left-handed  helix ;  Fig. 

183.       In     the     right 

_  Fiig.  183^  hand    helix,  the   sou ih 

pole  is  at  the  extrem- 
ity of  the  coil,  at  whic  h 
Left  Hand  Helix.  the     positive     elt  ctric 

current    enters    it;    in 

the  left  hand  helix,  the  south  pole  is  always  at  the  extremity, 
by  which  the  current  leaves  the  helix.  If  the  direction  of  the 
current  be  reversed,  the  poles  will  also  be  reversed.  It  is  not 
necessary  to  place  the  rod  of  iron  in  a  glass  tube ;  if  the  wire 
be  wound  with  some  good  non-conductor  of  electricity,  such  as 
silk,  or  cotton,  so  as  to  compel  the  electrical  current  to  circulate 
around  the  rod,  without  leaping  transversely  across  the  wires, 
or  entering  the  rod  itself,  the  same  end  will  be  attained.  Such 

397.  How  can  a  rod  of  iron  be  made  magnetic  by  the  current?  What  is  a  right  hand 
helix?  A  left  hand?  How  are  the  poles  of  each  arranged  ?  What  is  the  eJect  upon  tae 
poled  of  reversing  the  current  ? 


MAGNETISM  INDUCED  BY  THE  CURRENT.       377 

a  bar  of  iron,  converted  into  a  temporary  magnet,  by  the  induc- 
tive influence  of  an  electrical  current,  is  called  an  electro-mag- 
net. If  a  steel  rod  be  substituted  for  the  soft  iron  bar,  it  will 
become  permanently  magnetic.  The  same  effect  will  be  pro- 
duced upon  a  steel  needle  placed  in  the  centre  of  a  spiral  coil 
of  wire,  through  which  a  powerful  charge  of  frictional  electri- 
city from  a  Leyden  jar  is  transmitted.  If  a  wire,  carefully 
woun  I  with  fine  silk  or  cotton,  and  thoroughly  coated  with  shell- 
lae  dissolved  in  alcohol,  in  order  to  increase  its  non-conduct- 
ing power,  be  wound  several  times  around  the  iron  rod,  proceed- 
ing regularly  from  one  end  to  the  other  and  then  returning,  the 
magnetic  power  produced  by  the  circulating  current  will  be 
greatly  increased,  and  the  greater  the  number  of  co'ls,  the  more 
powerful  is  the  effect.  In  Fig.  184,  is  represented  a  coil  of 
this  description,  wound  into  the  form  of  a 
184-___  hollow  cylinder,  so  that  the  iron  rod  may 
be  withdrawn  at  pleasure.  If  the  rod  be 
removed,  and  the  connections  established 
with  the  battery  by  means  of  the  binding 
cups  arranged  below,  it  will  be  found  that 
the  ends  of  the  coil  have  themselves  become 
very  strongly  magnetic,  as  shown  by  their 

Magnet,  Mi'Ie  and  .LJ     ,.         ofj.  JL.  TP    . 

Unmade.  attraction  ot  iron  filings.     If  the  rod  be  now 

inserted,  this  will  become,  by  induction,  very 
strongly  magnetic,  and  support  quite  large  pieces  of  iron  brought 
near  the  poles;  these  pieces  of  iron  become  themselves  possessed 
of  magnetic  power,  and  will  support  additional  pieces,  so  that  quite 
a  long  chain  of  magnets  may  thus  be  formed  in  the  manner  rep- 
resented in  the  figure,  in  all  cases  the  north  pole  of  one  being 
opposite  the  south  pole  of  the  next.  If  the  connection  with  the 
battery  be  broken,  so  that  the  battery  current  ceases  to  flow 
through  the  coil,  the  magnetism  of  the  rod,  and  of  all  the  pieces 
of  iron,  is  at  once  destroyed,  and  the  keys  fall ;  if  the  connection 
be  reestablished,  the  magnetism  is  immediately  restored,  and  the 
keys  are  again  attracted.  In  this  manner,  by  forming  and 
breaking  the  connection  with  the  battery,  a  piece. of  soft  iron, 
may  be  magnetized  and  de-magnetized  at  pleasure.  If  a  mag- 
netic needle  be  brought  near  the  magnetized  rod  of  a  helix,  it 
will  be  thrown  into  violent  agitation  for  a  few  moments,  and 
then  have  one  of  its  poles  strongly  attracted  towards  one  of  the 

What  is  the  effect  of  carrying  the  wire  several  times  around  the  iron  bar?  What  is 
an  electro-magnet  ?  Describe  Fig.  184.  Ts  the  coil  itself  made  magnetic  by  the  passage 
of  the  current  ?  How  cau  an  electro-magnet  be  made  and  unmade  ? 


373  THE    GALVANOMETER. 

poles  of  the  rod.  If  it  be  the  north  pole  of  the  needle  which 
is  thus  attracted,  we  may  know  that  it  pom's  to  the  south  pole 
of  the  iron  rod,  and  thus  the  character  of  its  poles  may  be  de- 
termined. 

398.  USolecular  movements  during-  the  magnetization  of 
Bars.    The  induction  of  magnetism,  and   die  cessation  of  mag- 
netism, are  both  attended  witji  molecular  motion  throughout  the 
rod  of  iron.     The  rod,  on  becoming  magnetic,  acquires  a  si  ght 
increase  in  length,  and  suddenly  contracts   to  its  former  dimen- 
sions when  the  magnetism  ceases.     If  the  bar  be  supported  at 
one  end,  so  as  to  bend  under  its  own  weight,  it  becomes  stra'ght- 
ened  to  a  greater  or  less  extent  when  magnetized.     Each  time 
that  the  bar  becomes  magnetic,  or  loses  its  magnetism,  a  distinct 
sound  is  produced.     Finally,  the  molecular  movements,  if  re- 
peated in  quick  succession  by  rapidly  making  and  breaking  con- 
tact between  the  helix  and  the  battery,  so  as  quickly  to  magne- 
tize and  de-magnetize  the  rod,  produce  an  elevation  of  its  tem- 
perature, which  is  entirely  independent  of  the  heat  produced  in 
the  conducting  wire  by  the  flow  of  the  electrical  current.     These 
facts  are  possessed  of  great  interest,  as  connected  with  the  theory 
of  the  convertibility  of  Forces.   (See  §§  263  and  264.) 

399.  The  Galvanometer.    The  degree  of  movement  in  a 
magnetic  needle,  produced  by  the  passage  of  an  electrical  cur- 
rent, is  proportioned  to  the  streng'h  of  that  current,  and  may  be 
used,  therefore,  to  measure  its  intensity.     An  instrument  con- 
structed for  this  purpose,  is  called  a  Galvanometer.     Its  use  is 
restricted  to  the  measurement  of  currents  of  feeble  intensity, 
because,  when  the  current  reaches  a  certain  degree  of  strength, 
the  needle  immediately  assumes  a  position  at  right  angles  to  the 
wire,  and  flies  at  once  to  the  farthest  point  to  which  it  can  go, 
and  it  is  evident  that  it  can  measure  no  degree  of  strength  in 
the  electrical  current  beyond  that  which  will  drive  it  into  this 
position.     For  the  measurement,  however,  of  currents  of  elec- 
tricity of  low  intensity,  this  instrument  is  invaluable.     It  is  of 
two  kinds,  the  common,  and  the  astatic  galvanometer ;  in  the 
former,  a  common  magnetic  needle  is  employed ;  in  the  latter, 
an  astatic  needle.     In  the  common  galvanometer,  instead  of 
having  the  wire  connecting  the  two  poles  of  the  battery  pass 
once  directly  above  or  below  the  magnetic  needle,  it  is  bent,  and 
curried  first  beneath  the  needle,  and  then  brought  back  above 

998.  Describe  the  molecular  movements  which  take  place  during  the  magnetization  of 
bars  ?  What  effect  is  produced  upon  the  temperature  of  the  bar  by  rapid,  magnetization, 
and  demagnetization  ?-^-399,  Describe  the  common  galvanometer. 


THE    ASTATIC    GALVANOMETER. 


379 


The  Common   Galvanometer. 


185-  it,  as  represented  in  Fig.  185;  in  this 

manner,  the  effect  of  the  current  upon 
the  needle  is  doubled,  and  its  sensitive- 
ness to  the  passage  of  very  feeble  cur- 
rents greatly  increased.  In  the  most 
perfect  form  of  the  instrument  the  wire 
is  carried,  not  simply  once  around  the 
magnetic  needle,  but  several  times,  so 
as  to  constitute  a  longitudinal  coil, 
within  which  the  needle  plays  freely. 
When  the  instrument  is  to  be  used,  it 
is  placed,  with  the  coil  and  the  needle, 
in  the  magnetic  meridian ;  the  connec- 
tion is  then  formed,  and  the  electrical  current  transmitted ;  the 
needle  is  at  once  deflected  to  the  east,  or  west,  as  the  case  may 
be,  and  more,  or  less,  according  to  the  strength  of  the  current ; 
when  the  current  exceeds  a  certain  strength,  the  needle  assumes 
a  position  at  right  angles  to  the  coil,  and  ceases  to  measure  any 
additional  degrees  of  intensity. 

400.    The  Astatic  Galvanometer.    In  the  common  galvan- 
ometer, the  needle,  when  deflected   by  the  electrical  current, 
evidently  moves  in  opposition  to  the  magnetism  of  the  earth, 
which  tends  to  keep  it  in  the  magnetic  meridian,  and  the  dis- 
tance to  which  it  moves  is  not,  therefore,  a  correct  indication  of 
the  real  strength  of  the  current,  but  of  its  force  less  the  amount 
of  the  magnetic  attraction  of  the  earth.     If  this  attraction  be 
neutralized,  its  sensitiveness  to  the  in- 
fluence of  the  electrical  current  is  great- 
ly increased.     This  is  accomplished  by 
the  use  of  the  astatic  needle,  which,  as 
has  been  shown, (§  390,)  is  constructed  in 
such  a  way  as  to  be  free  from  this  influ- 
ence, in  consequence  of  the  counteraci  ing 
influence  of  opposite  poles.      The  con- 
ducting wire  is  carried,  as  in  the  last  case, 
first  under,  and  then  above,  the  lower 
need'e;  Fig.  186.       Such  a  needle  is 
indifferent    to    the    magnetism    of   the 
earth,  and  will  remain  without  change 

in  any  position  in  which  it  may  be  placed ;  in  practice,  how- 
ever, it  is  arranged  so  as  to  tend  slightly  to  occupy  a  north  and 


The  Astatic  Galvanometer. 


400.  Describe  the  astatic  galvanometer. 


*•  380    LIQUID  PART  OP  CIRCUIT  EXERTS  MAGNETIC  ACTION. 


The  Astatic  Galvanometer,  with  Coil  of  Wire. 


south  direction,  in  order  that 
it  may  possess  a  fixed  point 
from  which  its  motion  may  be 
measured.  This  galvanome- 
ter is  represented  in  section, 
in  Fig.  187;  G  is  a  glass  case, 
protecting  the  instrument  from 
dust,  and  currents  of  air;  d  is 
a  fibre  of  silk,  by  which  the 
needle  is  suspended  ;  n  s,  s  ny 
represent  the  compound  nee- 
dle with  reversed  poles  ;  c,  c, 
is  a  graduated  copper  plate,  to 
mark  the  movement  of  the 
upper  needle;  w,  w,  is  the 
coil  of  wire ;  b,  b,  are  the  bind- 
ing cups,  for  making  connections  ;  m,  m,  are  screws  for  level  ng ; 
and  /,  a  small  lever  for  adjusting  the  position  of  the  needle  upon 
the  graduated  copper  plate.  Such  an  instrument  is  sensitive  to 
the  feeblest  currents  of  electricity,  and  will  detect  that  which 
is  produced  by  two  bits  of  zinc  and  platinum  wire,  not  half  an 
inch  in  length,  placed  in  acidulated  water.  This  instrument  is 
invaluable  for  the  measurement  of  small  degrees  of  heat,  as 
well  as  of  electricity,  as  we  shall  see  hereafter. 

401.  The  liquid  part  of.  tho  voltaic  circuit  acts  upon  the 
Eflagneiic  Needle,,  That  the  electrical 
current,  in  every  part  of  its  course,  acts 
upon  the  magnetic  needle,  i.  e.,  in  the 
liquid  within  the  battery,  as  well  as  in 
the  wire  connecting  the  poles,  may  be 
beautifully  seen  in  Fig.  188.  A  needle, 
n,  5,  is  suspended  over  a  dish  of  acidu- 
lated water;  on  one  side  of  this  dish 
a  zinc  plate,  z,  is  placed,  and  on  the 
other  a  platinum  plate,  P;  the  needle 
must  be  placed  so  that  one  of  its  poles 
point  to  one  plate,  and  the  other  pole  to 
the  other.  If  the  two  plates  be  now 
connected  by  a  wire,  the  needle  will  be 
deflected,  and  will  place  itself  nearly 


Fig.  188. 


The  liquid  part  of  the  Circuit 
magnetic. 


parallel  to  the  plates. 


401.  Show  that  the  liquid  part  of  the  circuit  acts  upon  the  magnetic  needle. 


THE    LAWS.  OF    ELECTRO-MAGNETISM.  381 

402.  The  laws  of  Electro  -magnetism.    The  following  laws 
have  been  established  in  regard  to  the  production  of  magnetism 
by  the  electrical   current,  so  long  as  the   battery   current  is 
maintained  of  uniform  strength.     1st.  The  magnetism  induced 
in  any  given  rod  of  iron  is  proportioned  to  the  number  of  colls 
of  insulated  wire  which  are  wound  upon  the  rod ;  and  it  makes 
no  difference  whether  the  coils  are  uniformly  distributed  over 
the  whole  length  of  the  rod,  or  accumulated  towards  .its  two 
extremities.     2d.  The  diameter  of  the  coils  which  surround  the 
rod  does  not  influence  the  result,  provided  the  current  be  of 
uniform  strength,  the  effect  of  increase  of  distance  of  the  coil 
from  the  bar  being  compensated  by  the  increase  of  effect  produced 
by  the  additional  length  of  the  wire.     3d.  The  thickness  of  the 
wire  has  no  effect  upon  the  result.     4th.  The  energy  of  the 
magnetism  is  proportioned  to  the  strength  of  the  current.     5th. 
The  retentive  power  of  the  magnet  increases  as  the  square  of 
the  intensity  of  the   magnetism.       6th.  The  intensity  of  the 
magnetism  is  proportioned  to  the  surface  which  the  rod  exposes  ; 
and  in  cylindrical  rods  is  as  the  .square  of  the  weight ;  bundles 
of  separate  wires  expose  a  larger  surface  than  a  solid  rod,  and 
hence  are  susceptible  of  a  higher  amount  of  magnetism  than  a 
solid  bar  of  equal  weight.     7th.  The  employment  of  long  rods 
possesses  this  advantage  over  short  rods,  that  the  neutralizing 
influence  of  the  two  poles  upon  each  other  is  lessened.     8th. 
The  increase  of  magnetic  energy  by  the  increase  in  the  strength 
of  the  electric  current,  proceeds  up  to  a  certain  point,  but  there 
is  a  limit  to  the  amount  of  magnetic  force  which  can  be  devel- 
oped in  iron,  although  the  amount  of  electric  action  may  be 
indefinitely  increased. 

403.  Ampere's  theory  of  Magnetism.     Ampere's   theory 

of  magnetism  is,  that  in  every 
magnet  there  are  currents  of 
electricity  circulating  around  it 
at  right  angles  to  a  line  joining 

Ampere's  Theory  of  Magnetism.  the  tw°  P°leS>  Fi9'  189>  Rnd  tl){lt 

these  currents  are  the  source  of 

the  magnetic  force.  In  the  ordinary  magnetic  needle,  which  is 
pointing  north  and  south,  these  electrical  currents  ascend  on 
the  western  side,  and  descend  on  the  eastern.  This  theory  is 
.founded  upon  the  magnetic  properties  possessed  by  a  helix, 
through  which  a  current  of  electricity  is  circulating.  If  a 

402.  State  the  laws  of  electro-magnetism. — 403.  State  Ampere's  theory  of  magnetism. 


382 


AMPERE  3    THEORY    OF    MAGNETIS1F. 


Fig.   190. 


The  Magnetism  of  a  Wire  Helix  carrying  the  Current. 


simple  helix  of  thin 
wire  be  freely  sus- 
pended in  the  man- 
ner represented  in 
Fig.  190,  by  a  hook 
dipping  into  a  cup 
containing  mercury, 
and  supported  at  the 
lower  end  in  a  simi- 
lar cup  of  mercury, 
as  soon  as  the  elec- 
trical current  is  made 
to  circulate  in  a  down- 
ward direction,  the  he- 
lix will  acquire  mag- 
netic properties,  as 
represented  in  the  figure,  and  assume  a  north  and  eouth  posi- 
tion ;  if  suspended  upon  a  point,  it  will  assume  a  position  par- 
allel to  the  dipping  needle.  The  helix  will  also  be  subject  to 
attraction  and  repulsion  by  the  poles  of  another  helix,  similarly 
mounted,  and  in  short,  exhibit  all  the  properties  of  a  common 
bar  magnet;  Fig.  191.  Hence  the  supposition  that  the  com- 
mon magnet  is  nothing  but 
an  iron  bar,  around  which  a 
similar  current  of  electricity 
is  continually  circulating. 
The  cause  of  these  currents 
is  not  known.  The  mag- 
netism of  the  earth  is  sup- 
posed to  be  produced  by 
currents  of  electricity  circu- 
lating continually  around  it 
from  east  to  west,  perpen- 

TWO  Magnetic  Helices.  dicular  to  the  magnetic  me- 

ridian ;    these   are  thought 

to  be  thermo-electric  currents,  due  to  the  variations  of  tempera- 
ture, resulting  from  the  successive  presence  of  the  sun  upon  dif- 
ferent parts  of  the  surface  of  the  globe  from  east  to  west, 
and  by  their  circulation  they  produce  the  north  and  south 

On  what  is  this  theory  founded?  Describe  the  movements  of  a  helix  carrying  the  cur- 
rent. Show  how  two  mounted  helices,  carrying  the  current,  affect  each  other  Explain 
the  magnetism  of  the  earth  in  Ampere's  theory.  Expbtin  how  the  electrical  currents  of 
the  earth  circulate  from  east  to  west,  while  those  of  the  uiaguet  circulate  from  west  to 
east. 


Fig.    191. 


THIS    THEORY    SATISFACTORILY    EXPLAINS 


383 


magnetic  poles  of  the  earth,  and  give  a  fixed  direction  to  the 
magnetic  needle  of  the  compass.  That  these  currents  circulate 
from  east  to  we  it,  while  those  of  the  ordinary  magnet  circulate 
from  west  to  east,  (=ee  Fig.  189,)  is  explained  by  the  fact,  that 
the  north  magnetic  pole  of  the  earth  really  corresponds  with 
the  south  pole  of  th3  ordinary  magnet;  and  if  the  south  pole 
of  the  ordinary  magnet  be  turned  towards  the  north,  it  will  be 
seen  that  the  currents,  in  this  case,  Fig.  189,  really  flow  from 
east  to  west,  just  as  in  the  ca~e  of  the  earth. 

40 1.  The  magnetic  effect  of  the  wire  carrying  the  galvanic 
current  accounted  for  by  Ampere's  Theory.  It  has  been 
found  that  when  two  wires  are  freely  suspended  near  each  other, 
and  galvanic  currents  are  transmitted  through  them,  the  wires 
will  repel  each  other,  if  the  currents  pass  in  opposite  directions, 
but  they  will  attract  each  other  if  the  currents  be  in  the  same 
direction.  If  the  two  wires,  moreover,  through  which  the  cur- 
rent is  passing  in  the  same  direction,  be  not  exactly  parallel,  but 
cross  each  other  at  an  angle,  they  will  tend  to  place  themselves 
in  parallel  lines.  Now  if  it  be  granted  that,  in  every  straight 
mignet,  electrical  currents  are  continually  circulating  in  a  direc- 
tion at  right  angles  to  a  line  joining  the  magnetic  poles,  we  see 
plainly  the  reason  why  a  magnet  tends  to  place  itself  at  right 
angles  to  a  wire  connecting  the  poles  of  the  battery,  and  carry- 
ing the  galvanic  current,  viz.,  that  by  such  a  movement  the  elec- 
trical currents  in  the  wire,  and  in  the  magnet,  assume  a  direc- 
tion parallel  to  each  other.  Let  p  Q,  in  Fig.  192,  repre  ent  a 

wire  carrying  the  galvanic  current 
in  the  direction  of  the  arrow,  and 
let  N  indicate  the  north  pole  of  a  bar 
magnet,  around  which  electrical  cur- 
rents are  supposed  to  be  circulating 
in  the  same  direction  as  in  the  wire  ; 
according  to  the  above  theory,  these 
electric  currents  will  necessari'y 
tend  to  arrange  themselves  parallel 
to  each  other,  and  the  magnet  assume 
a  position  at  right  angles  to  the 
wire.  On  the  other  hand,  if  the 
•magnet,  N,  be  fixed  in  an  upright 
position,  so  that  it  can  not  move,  and  the  wire,  r,  Q,  be  suspended 

404.  When  the  galvanic  current  is  transmitted  through  the  wires  in  opposite  directions, 
what  effect  is  produced?     If  in  the  same  direction?     If  the  two  wires  in  the  last  case  be 
not  exactly  parallel,  what  effect  is  produced?     How  does  this  explain,  according  to  Am- 
pere's; theory,  the  effect  of  the  wire  on  the  magnetic  needle  ? 
10* 


192. 


P 

1 

n 

II 

ml 

Q 

i 

The  magnetic  influence  of  the  Wire 
explained. 


:    4 


tttK   MAGNETIC   KFfKCT   OP  THE 


fVeely  parallel  to  It,  as  soon  as  the  gnlvnnic  current  begins  to 
circulate  from  P  to  Q,  tin;  wire  will  tend  to  move,  and  as*urne 
a  position  at  right  angles  to  the  magnet.  Tint*,  the  notion  of 
the  magnet  and  the  wire  is  reciprocal  ;  they  both  tend  equally 
to  move  into  such  a  portion,  in  reference  to  each  other,  that  (lie 
electric  currents  in  both  will  he  parallel,  and  that  one*,  of  the 
two,  will  actually  move,  which  to  the  leant  permanently  fixed, 
That  the  wire  carrying  the  current  doe*  actuiilly  move,  «o  as  to 
mljn*t  iinelf  tf)  the,  magnet,  may  he  nhown  by  the  apparatus 
in  Fig.  100.  Let  tt  plate  of  zinc,  z,  be  connected 
by  a  wire  with  the  cop- 
per plate,  (!,  and  both  be 
Mirtpcndcd  in  a  little  gla?* 
vewel  containing  acidu- 
lated water,  which,  by 
the  Aid  of  iv  piece  of 
eork,  t),  ia  made  to  float, 
in  A  ve*«el  of  water.  In 
this  CA»e,  the  galvanic, 
current  to  circulating,  as 
indicated  by  the  arrows, 
from  west  to  east.  If 
now  the  north  pole  of  A 
permanent  magnet  be 
presented  to  the  wire,  as 
it*  electrical  current*  are 
also  circulating  from 


Rirts  Ktf^, 


to  enst,  an<1  are  parallel  to  those  of  the  loop,  the  liitle  bat- 
tery will  maintain  its  jmMtion,  the  only  effect  being,  Hint  it  will 
be  attracted  by  the  magnet,  and  finally  place  it«<  It'  midway  be- 
if    kWO  poles  \  but  if  the  south  pole  of  the  magnet  be  pre- 

i  i..  it.  tin  ,  i<  ,,i  ,.il  currents  of  which  are  rnul.ii  n 

,  -I,  in  llx>  reverse  dilMiCtion  from  tboM-  of  ilu-  \MIV. 
Ilir  <!<niin.r  b:i1l<-r\  \\ill  lir-i  l.r  impelled  fixm\  the  ma-'iH-l.  lln-n 
lurni'd  «-tnnplrlrl\  :«n.iin.l.  nnt.l  tl.«-  ;':.lv:nu.-  i-urr.  nl  «-ii,  \il:i1c  -  in 
llic  wami'  dirn'ti.  \\  :\  \\\  lli«  \\\-.\  :MIC-I.  from  i-n-'t  In  \\«>  I.  niicl  >li" 
tWOb<  ">in<  paralltl;  .•»'>,!  fm:ill\  \\ill  !•<•  Ml  I  !•;».•:«  .1  M  .  l.rlorr.  mil  il 

ii  ooeupiw  :•  position  mklwt^  between  ih«-  twopo'w*    If  th«- 

..-fixmof  the   r:irlh   !)<'    j  MS  wngg«*ti'd   in  il.«     1.-  t 


"I.    >'li<n    I;..  ••     •>. 

. 

-  «Mr>-li\g  «»«  «urrettt?    i 


THE    ACTION     OF    TIIE    WIRE 


385 


article,  by  thermo-electric  currents  circulating  around  it  from 
east  to  we>t,  perpendicular  to  the  magnetic  meridian,  it  i-  evi- 
d -nt  that  a  win-,  carrying  the  galvanic  current,  it'  freely  sus- 
pended, ought  to  arrange  itself,  according  to  the  above  princi- 
ple-;, parallel  to  these  currents,  and  at  right  angles  to  the  mag- 
netic meridian.  This  i-^  found  to  be  the  case,  and  it  constitutes 
a  remarkable  confirmation  of  the  truth  of  Ampere's  theory.  If 
the  curved  wire,  Fig.  194,  be  suspended  from  mercury  cups, 


\ 

'  the  magnetism  of  the  Earth,  upon  the  icire  carrying  Ike.  Currint. 

so  that  it  can  move  freely,  and  be  turned  so  that  its  plane  coin- 
cities  with  the  magnetic  meridian,  it  will  remain  in  that  position 
until  a  connection  is  formed  with  the  battery,  and  a.  current 
p:i—  eil  through  it.  When  this  takes  place,  it  will  be  seen  to 
turn  slowly  around  the  pivots,  so  as  to  take  a  position  at  right 
angles  to  the  magnetic  meridian,  and  parallel  to  the  thermo- 
electric currents  supposed  to  be  circulating  from  east  to  w».-st. 
It  will  turn  in  such  a  direction  that  the  current  in  the  lower 
part  of  the  hoop  will  also  be  from  east  to  west.  Other  rota- 
tions, of  a  similar  kind,  may  be  explained  upon  the  same  theory, 
but  it  is  not  necessary  to  pursue  the  subject  farther.  -The 
main  fa  't  is,  that  the  galvanic  current,  traversing  a  wire,  pro- 
duces magnetic  forces  on  lines  at  right  angles  to  its  length,  and 
induces  magnetism  in  a  bar  of  soft  iron  placed  across  it  perpen- 
dicularly. 


Explain  Fig.  Wi.     What  is  the  main  fact .' 


386 


AND    THE    MAGNET    RECIPROCAL. 


Horse  Shoe.  Electro- 
Magnet. 


196- 


Fig.  195.  405.   The  most  powerful  form  of  Electro- 

BZaguets.—  Horse-Shoe  Blag-nets.  By  increas- 
ing the  number  of  coils  upon  a  straight  rod 
of  iron,  its  magnetic  power  may  be  indefinitely 
increased.  But  the  best  mode  of  arranging 
magnets  of  this  kind  is  to  bend  the  iron  bar  into 
the  form  of  a  horse-shoe,  as  shown  in  Fig.  195, 
and  then  to  wind  it  with  copper  wire,  wrell  cov- 
ered with  cotton,  or  silk  thread,  and  thoroughly 
insulated.  The  two  poles  can  thus  be  brought 
very  near  to  each  other,  and  their  combined 
magnetic  power  concentrated  upon  the  same 
object  at  the  same  moment.  The  two  arms 
must  both  le  wound  in  the  same  direction,  in  order  ihat  their 

effect  may  coincide  and 
produce  but  two  poles, 
one  at  each  extremity 
of  the  curved  bar.  As 
soon  as  a  connection  is 
formed  with  the  bat- 
tery, the  curved  bar 
becomes  a  very  power- 
ful magnet,  with  its 
north  pole  at  the  end 
where  the  electrical 
current  enters,  and  the 
so'Jth  pole,  at  the  end 
where  it  issues,  as 
shown  in  Fig.  196, 
and  will  raise  a  very 
heavy  weight  ;  but  as 
soon  as  the  connection 
with  the  battery  is 
broken,  the  magnetic 
power  is  destroyed, 
and  the  weight  falls 
with  a  crash.  Mag- 
nets have  been  con- 
structed in  this  form 
which  would  suspend 

Large  Electro-Magnet.  2,000  Or  3,000  Ibs.,  and 


405.  What  is  the  most  effective  form  of  the  electro-magnet  ?    What  effects  have  been 
produced  by  powerful  magnets  of  this  kind? 


CUliVCD    ELECTRO-MAGNETS. 


387 


in  some  cases  10,000  Ibs.  By  making  and  then  breaking  tlie 
current  circulating  around  such  an  electro-magnet,  we  can  bring 
into  play  or  annihilate  at  once  this  immense  force.  The  iron 
bar  below  the  poles  is  called  the  armature  of  the  magnet,  and 
the  effect  is  very  greatly  increased  if  it  also  consists  of  an  elec- 
tro-magnet, inverted,  with  poles  opposite  to  those  in  the  upper 
magnet,  and  magnetized  by  the  same  current.  As  soon  as  the 
connection  is  formed  with  the  battery,  these  two  electro-mag- 
nets rash  togsther  with  great  power,  and  with  a  current  of  mod- 
erate intensity,  are  capable  of  supporting  a  weight  of  several 
tons.  It  has  also  been  found  that  the  power  is  greatly  increased, 
if  the  helix,  instead  of  being  made  of  a  continuous  wire,  be 
formed  of  several  wires  of  limited  length,  each  having  its  own 
connection  with  the  battery.  An  electro -magnet,  constructed 
on  this  principle,  can  be  made  to  lift  more  than  a  ton  with 
a  single  cylinder  battery  of  small  size.  The  same  principle 
is  well  illustrated  by  what  is  called  the  magic  circle,  repre- 
sented in  Fig.  197.  Two  semi-circles  are  made 
Fig.  197.  of  a  stout  bar  of  soft  iron,  and  well  fitted  together 
so  as  to  form  a  circle,  and  include  a  small  helix 
of  wound  wire,  H,  the  two  ends  of  which  are  to 
be  connected  with  the  poles  of  a  small  battery. 
When  the  connection  is  made,  it  will  be  difficult 
to  pull  the  semi-circles  apart,  and  a  very  consider- 
able weight  may  be  raised;  but  the  instant  the 
connection  is  broken,  the  semi-circles  fall  apart 
of  themselves. 

406.  The  Magnetic  Telegraph.  Advantage 
is  taken  of  this  power  to  make  and  to  unmake  a 
magnet,  by  means  of  transmitting  and  breaking 
a  current  of  electricity,  in  the  construction  of  the 
magnetic  Telegraph.  This  is  the  most  important 
of  the  uses  which  have  been  made  of  galvanic 
electricity,  and  it  deserves  a  minute  description. 
Magic  circle.  The  electric  telegraph  consists  of  three  parts, 
viz. :  1st,  the  battery,  or  source  of  electric  power ; 
2d,  the  wire  for  the  transmission  of  the  current ;  and  3d,  the 
electro-magnetic  instrument  for  making  the  signals.  1st.  The 
battery.  Any  form  of  the  galvanic  battery  may  be  employed ; 
but  the  most  common  form  is  Daniell's  constant  battery.  Two 
batteries  are  required  in  order  to  establish  telegraphic  commu- 


Describe  the  magic  circle. — i05.  What  is  the  magnetic  telegraph  I 


"388  THE    MAGNETIC    TELEGRAPH. 

mcation  in  both  directions  between  two  places,  one  at  each  end  of 
the  line.  2d.  The  wire.  There  must  be  a  wire  extending  be- 
tween the  two  places,  in  order  to  convey  the  current.  This  wire  is 
connected  with  either  pole  of  the  battery,  and  is  then  carried 
upon  posts,  15  or  20  feet  in  height,  to  the  distant  place.  It  is 
usually  made  of  copper  or  iron,  and  is  attached  to  the  posts  by 
some  non-conducting  substance.  Sometimes  it  is  insulated 
.  by  a  suitable  covering  and  buried  in  the  ground,  but  it  is  prefer- 
able to  carry  it  through  the  air,  on  account  of  the  facility  with 
which  breaks  may  be  discovered  and  repaired.  When  it  reaches 
the  distant  place,  it  is  connected  with  an  electro-magnet,  which 
then  becomes  part  of  the  line,  and  on  leaving  the  electro-mag- 
net, is  conveyed  to  a  large  iron  plate,  buried  in  a  moist  spot 
in  the  ground,  and  there  terminates.  The  electrical  current, 
starting  from  the  positive  pole  of  the  battery,  traverses  the 
wire  to  the  distant  place,  circulates  around  the  electro-magnet, 
then  passes  to  the  iron  plate,  and  thence  through  the  earth,  back 
to  the  negative  pole  of  the  battery,  and  thus  the  circuit  is  made 
complete.  It  was  at  first  supposed  that  a  second  wire  was  re- 
qu'red  to  bring  the  current  back  from  the  distant  point,  after  it 
had  passed  through  the  electro-magnet,  in  order  that  a  connec- 
tion might  be  formed  with  the  opposite  pole  of  the  battery; 
but  it  was  afterwards  ascertained  that  the  earth  would  answer 
as  well  a»  a  second  metallic  wire,  the  great  extent  of  conducting 
area  which  it  exposes  compensating  for  its  feeble  conducting 
power.  In  this  manner  a  current  is  made  to  pass  to  any  distant 
town,  and  to  excite  magnetism  in  an  electro-magnet  as  soon  as 
the  wire  is  connected  with  either  pole  of  the  galvanic  bat- 
tery ;  and  then  when  the  connection  with  the  battery  is  broken, 
this  current  can  be  made  to  cea>e,  and  the  electro-magnet  at  the 
distant  place  de-magnetized.  By  this  arrangement  it  is  evident 
that  a  magnet  can  be  made  and  unmade  at  any  place,  however 
distant,  by  simply  making  or  breaking  the  connection  between 
the  wire  and  the  battery.  3d.  The  instrument.  Having  now  the 
means  of  creating  a  magnet  at  the  point  with  which  we  wish  to 
communicate,  we  have  the  means  of  producing  motion,  and  giv- 
ing signals.  Two  instruments  are  required,  one  at  each  end  of 
the  line,  for  the  purpose  of  receiving  messages  from  both  direc- 
tions, constructed  on  the  following  plan.  Let  an  armature,  con- 
sisting of  a  piece  of  soft  iron,  be  suspended  from  one  end  of  a 

What  are  the  three  essential  parts  of  the  telegraph  ?  How  many  batteries  are  required  ? 
How  many  wires?  How  does  the  electrical  current  return  from  the  distant  |--ce  '.  ijow 
many  instruments  are  required  i 


THE   LINE.  389 

lever,  about  one-tenth  of  an  inch  above  the  poles  of  an  electro- 
magnet, placed  firmly  upon  a  pedestal,  and  with  its  two  arms 
projecting  upwards,  in  the  manner  of  the  letter  U.  It  is  obvi- 
ous that,  when  the  current  is  circulating,  this  armature  will  be 
drawn  to  the  magnet,  and  that  the  opposite  end  of  the  lever 
will  be  correspondingly  elevated.  If  a  steel  point  be  at- 
tached to  the  upper  side  of  the  distant  end  of  the  lever,  and  a 
piece  of  paper  be  fastened  firmly  within  one-tenth  of  an  inch 
of  it,  a  dot  will  be  made  upon  the  paper  whenever  the  arma- 
ature  is  drawn  down,  anJ  the  steel  point  flies  up.  When 
the  connection  with  the  battery  is  broken  by  the  operator,  at  the 
place  from  which  the  message  is  transmitted,  the  armature  is 
released,  and  the  distant  end  of  the  lever  falls.  As  soon  as  the 
connection  is  formed  again,  the  steel  point  again  flies  up  and 
strikes  the  paper  a  second  time.  If  the  paper,  instead  of  being 
stationary,  is  in  motion,  and  carried  steadily  along  upon  a  ro  ler, 
the  second  dot  will  not  coincide  with  the  first,  and  if  the  steel 
point  be  pressed  for  some  minutes  against  it,  a  long  mark  will 
be  formed.  Thus  the  operator  at  the  other  end  of  ihe  line  has 
the  means  of  impressing  dots,  and  broken  or  continuous  lines, 
upon  paper,  at  the  place  to  which  the  message  is  to  be  sent,  each 
one  of  which  may  be  mads  to  represent  a  letter,  and  their  com- 
binations, words  and  sentences.  The  return  mes  age  requires 
a  similar  arrangement;  first,  there  must  be  a  battery;  for  the 
wire,  the  original  wire  may  be  employed,  disconnected  from  the 
electro-magnet  just  employed,  and  connected  with  the  positive 
pole  of  the  battery  at  that  end  of  the  line;  then  there  mu>t  be 
an  electro-magnet  at  the  first  place,  which  must  be  connected 
with  the  line  on  the  one  hand,  and  on  the  other,  with  an  iron 
plate,  buried  in  the  ground.  The  operator  to  whom  the  original 
message  was  sent,  must  have  the  means  of  sending  an  electrical 
current  back  to  the  electro-magnet  at  the  first  place,  and  then  es- 
tablishing a  connection  between  it  and  the  ground,  so  that  it  may 
return  to  him  through  the  earth,  and  he  replies  by  making  and 
breaking  the  connection  between  the  wire  and  the  battery  under 
his  control.  Thus  the  electrical  current  is  made  to  pass  to  the 
first  pla-.-e,  there  impress  dots  and  lines  on  paper,  in  the  manner 
already  describee!,  then  descend  to  the  iron-plate,  and  so  return 
through  the  earth  to  the  opposite  pole  of  the  second  battery. 
This  is  an  outline  of  the  system  known  as  Morse's  telegraph. 
A  sketch  of  it  is  given  in  Fig.  198;  c,  z,  represents  the  bat- 

Explaiu  the  principle  on  which  they  are  constructed. 


390 


THE    INDICATOR. 

Fig.  198. 


Current  passing  tkrougk  the  Earth. 

tery ;  n  and  jt>,  the  iron  plates ;  the  arrows,  the  course  of  the 
current.  There  are  other  systems,  but  the  principle  is  the 
same  in  all,  the  chief  difference  consisting  in  the  arrangement 
of  the  electro-magnetic  instrument. 

407.    morse's  Blectro-Magnetic  Indicator.    In  Fig.  1 99,  is 
given  an  exact  representation  of  the  instrument  used  for  mak- 

Fig.  199. 


Morsels  Telegraphic  Indicator. 

ing  the  signaK  F  E  represents  the  electro-magnet  which  is  made 
and  unmade  by  forming  and  breaking  the  electrical  connection 
at  the  opposite  end  of  the  telegraphic  line.  The  connection 
between  the  instrument  and  the  main  wire  is  formed  at  the  points 

Explain  Fig.  198.— 407-  Describe  Morse's  indicator. 


THE    MANIPULATOR.  391 

a  and  b ;  a  is  connected  with  the  wire  bringing  the  message,  b 
with  the  iron  plate  buried  in  the  ground.  D  is  a  piece  of  soft 
iron,  which  is  drawn  down  upon  the  poles  of  the  magnet  when- 
ever the  circuit  is  completed,  and  is  raised  again,  whenever  the 
current  is  broken,  by  the  spring  r  attached  to  the  opposite  end 
of  the  lever  A ;  m,  m,  are  two  screws  for  regulating  the  play 
of  this  lever.  At  the  extreme  end  of  A,  is  a  sharpened  point 
which,  when  D  is  drawn  down  by  the  completion  of  the  circuit, 
strikes  against  the  band  of  paper  upon  the  under  side  of  the 
roller,  H.  This  band  of  paper  is  continually  moved  forward  by 
means  of  clock  work  carried  by  the  weight,  p.  If  the  electrical 
circuit  be  formed,  and  then  instantaneously  broken  by  the  ope- 
rator at  the  station  from  which  the  message  is  sent,  the  sharp 
point  merely  strikes  the  paper,  and  is  immediately  withdrawn 
by  the  spring,  r,  leaving  only  a  dot  behind  it ;  but  if  the  circuit 
be  maintained  for  an  appreciable  interval,  the  point,  remaining 
longer  in  contact  with  the  paper,  leaves  a  line  or  mark  behind 
it.  Thus  a  long  continuous,  or  broken  line,  may  be  produced, 
or  a  succession  of  dots  ;  and  a  set  of  different  signals  constructed, 
corresponding  with  the  letters  of  the  alphabet.  B  is  a  roller, 
around  which  the  band  of  paper  is  wound.  With  this  instru- 
ment it  is  necessary  to  translate  the  signals  that  are  formed  into 
the  letters  which  they  represent;  but  instruments  of  a  much 
mare  complicated  character  have  been  constructed,  in  which  the 
message  is  recorded  in  printed  letters.  The  instrument  for  ac- 
complishing this,  was  invented  by  Mr.  House,  and  is  a  wonder- 
fully ingenious  piece  of  mechanism.  Mr.  Bain  has  invented  a 
telegraphic  system,  in  whi^h  no  electro-magnet  is  used,  but  only 
the  chemical  influence  of  the  current  operating  upon  paper  pre- 
pared with  cyanide  of  potassium. 

408.  -JL'he  Telegraphic  manipulator  and  IVIorse's  Alphabet. 
The  instrument  by  which  the  message  is  transmitted  to  the  distant 
place,  is  called  the  Manipulator,  Jt  consists  of  a  wooden  stand, 
Fig.  200,  upon  which  is  a  metallic  lever,  «,  b,  turning  iipon  a 
horizontal  axis ;  L  is  a  wire  communicating  with  the  line ;  B,  a 
wire  forming  a  connection  with  the  local  battery;  and  A, 
a  wire  connected  with  the  iron  plate  in  the  ground.  At  #, 
there  is  a  spring,  by  which  the  lever  is  raised  and  prevented 
from  touching  the  metallic  button  under  it ;  and  so  long  as  this 
is  the  case,  there  is  no  connection  between  the  local  battery  and 
the  line,  and  consequently  no  flow  of  the  current  to  the  distant 
place  ;  but  there  is  a  connection  with  the  local  indicator,  and, 

408.  Describe  Morse's  manipulator  and  alphabet. 


392 


MORSE'S    ALPHABET. 


The  Telegraphic  Manipulator. 


FiS-  20°-  through  it, 

with  the  line 
and  the  dis- 
tant battery 
on  the  01  ;e 
hand,  and 
with  the  iron 
plate,  or  the 
ground,  on 
the  other,  eo 
that  the  in- 
strument, in 

this  state,  is  always  in  a  suitable  condition  for  receiving  a  mes- 
sage. When  it  is  desired  to  transmit  a  message,  pressure  is 
applied  to  the  wooden  knob,  and  the  lever  brought  down  upon 
the  metallic  button  connected  with  the  local  battery,  B,  when  a 
current  immediately  circulates  through  the  point  x,  into  the 
lever,  then  through  m,  into  the  line,  and  continues  as  long  as 
pressure  is  applied  upon  the  knob.  Thus,  by  the  depression 
and  elevation  of  the  knob,  K,  a  succession  of  dots  and  broken 
lines  may  be  impressed  upon  paper  in  the  Indicator  at  the  other 
end  of  the  line,  and  it  is  only  necessary  to  give  these  combina- 
tions a  definite  meaning.  The  alphabet  adopted  by  Morse  is 
represented  in  the  following  table. 


A        -  — 
B        

0        --    - 
D        
E 
F        
Q. 

J        
K       
L        

M       

N        —  - 
0        -    - 

S 
T        — 
U          -  — 
V           
W         
X          

H        
I 

2    :•- 

z        --  - 

& 

In  this  manner  words  and  sentences  can  be  arranged,  care 
being  taken  to  leave  a  space  between  each  letter.  During  the 
process  of  transmission  a  continual  clicking  proceeds  from  the 
armature  of  the  Indicator  where  the  message  is  received,  and 
so  clear  and  definite  are  these  sounds  to  the  practised  ear,  that 
the  message  can  be  interpreted  by  these  sounds  alone,  without 
having  recourse  to  the  paper,  and  in  many  telegraph  offices  no 
other  Indicator  is  employed  than  an  electro-magnet,  and  movable 
armature,  the  pen  and  paper  being  dispensed  with.  The  same 
manipulator,  wThen  not  used  to  transmit  messages,  is  employed 
for  their  reception ;  the  current  from  the  distant  place  eaters  by 


THE    RELAY.      .  393 

the  wire,  L,  passes  through  m,  to  the  metallic  lever,  thence 
through  b,  to  the  wire  A,  and  by  it  is  transmitted  to  the  Indicator. 
409.  The  Relay*  In  describing  the  Indicator,  we  have 
supposed  that  the  current,  after  traversing  the  line,  entered  di- 
rectly into  the  electro-magnet,  and  worked  the  armature ;  but 
wheii  the  current  has  proceeded  a  few  miles,  it  can  not  act  with 
sufficient  force  upon  the  electro-magnet  to  communicate  the 
message.  It  can  only  be  used  to  establish  a  communication 
between  a  fresh  battery  at  the  place  where  the  message  is  sent, 
and  the  Indicator.  The  current  then,  instead  of  entering  direct- 
ly into  the  Indicator,  is  carried  into  another  instrument,  called 
the  Relay,  Fig.  201,  enters  the  electro-magnet,  E,  through  the 

Fig.  201. 


The   Telegraphic  Relay. 

binding  screw,  L,  and  after  traversing  the  coils,  descends  into 
the  earth  by  the  binding  screw,  T,  and  returns  back  to  the 
battery  from  which  it  started.  Each  time  that  a  current 
passes  over  the  line,  and  traverses  the  electro-magnet,  E,  it  at- 
tracts an  armature,  A,  which  is  suspended  from  a  horizontal 
axis,  and  is  extended  up  into  a  vertical  rod,  p.  Whenever 
the  armature,  A,  is  drawn  towards  the  electro-magnet,  it  drives 
the  lever,  ;?,  in  the  opposite  direction,  against  a  button,  n ;  as 
soon  as  p  touches  w,  a  powerful  current  from  the  positive  pole 
of  a  fresh  battery  placed  beneath  the  table,  and  not  seen  in 
the.  figure,  enters  at  r,  passes  up  the  pillar,  m,  to  n,  then  down 
p,  to  <?,  and  from  that  to  the  binding  cup,  z,  whence  it  flows 

409.  Describe  the  construction  and  uses  of  the  Kelay. — 209.*  Describe  the  arrange- 
ment of  the  line,  with  its  batteries  and  instruments.  Describe  the  exteusiou  of  Tele- 
graphic communicatioa. 


394      MESSAGES  INTERPRETED  BY  SOUND  ALONE. 

to  the  electro-magnet  of  the  Indicator,  where  it  records  the  mes- 
sage in  the  usual  manner,  and  thence  returns  to  the  negative 
pole  of  the  supplemental  battery.  Thus,  whenever  the  electro- 
magnet of  the  Relay  is  excited,  however  feebly,  by  the  current  of 
the  line,  the  electro -magnet  of  the  Indicator  is  also  excited  for 
the  same  length  of  time,  by  the  current  of  the  fresh  battery, 
and  all  the  feeble  signals  of  the  first  electro-magnet  are  power- 
fully repeated  by  the  second,  and  with  sufficient  force  to  transmit 
the  message.  As  soon  as  the  electro-magnet,  E,  ceases  to  act, 
the  armature,  A,  is  released,  the  spring,  r,  draws  p  away  from 
n,  and  the  current  of  the  second  battery  ceases  to  circulate 
through  the  electro -magnet  of  the  Indicator.  With  a  battery  of 
25  of  Grove's  elements,  the  current  is  strong  enough  at  100 
miles  from  its  starting  point  to  excite  the  electro-magnet  of  the 
Relay,  and  bring  into  operation  the  second  battery,  by  which  the 
Indicator  is  set  in  motion,  and  the  message  recorded.  For  a 
lo  ger  distance,  a  new  current  must  be  thrown  into  the  line. 
This  new  current  may  be  introduced  at  any  station,  from  a 
battery  of  20  or  30  elements,  provided  for  the  purpose,  by  con- 
necting the  wire  from  its  positive  pole  with  a  metallic  pillar 
placed  immediately  below  the  armature,  D,  Fig.  199,  but  not 
touching  it,  except  when  the  armature  is  drawn  down ;  when 
this  takes  place,  the  current  enters  the  armature,  and  passes 
directly  from  it  to  the  wire  of  the  line,  which  carries  it  on  to 
the  following  post.  Thus,  with  every  signal  which  is  formed  by 
the  Indicator,  a  corresponding  amount  of  electricity,  of  greater 
strength,  from  a  fresh  battery,  is  sent  down  the  line,  and  so 
the  despatch  is  transmitted  from  post  to  post.  The  battery 
used  for  this  purpose  is  distinct  from  that  used  in  connection 
with  the  Relay  just  described.  The  use  of  local  batteries,  and 
the  restoration  of  the  strength  of  the  main  current  by  supple- 
mental batteries,  seems  to  be  due  to  Prof.  Henry  of  the  Smith- 
sonian Institute.  As  messages  are  now  generally  interpreted 
by  sound  alone,  the  telegraphic  Indicator,  Fig.  199,  is  seldom 
employed  except  in  small  offices,  and  in  place  of  it  a  simple 
electro-magnet  with  movable  armature  is  substituted,  arranged 
in  such  a  manner  as  to  intensify  the  sounds,  and  called  the 
Sounder;  this  instrument  is  connected  with  the  Relay  in  the 
same  manner  as  the  Indicator,  by  which  its  connection  with 
the  lo  \al  battery  is  established,  as  already  described. 

409.*  The  Telegraph  line  a  Closed  Circuit.  The  Message 
sent  by  Breaking  the  Circuit.  The  telegraph  wire  and  the 
earth,  together  form  an  immense  electrical  circuit,  having  a 
powerful  galvanic  battery  included  in  it.  One  battery  may  be 


THE    TRANSMISSION    OF   MESSAGES.  395 

used  to  actuate  the  circuit,  which  may  be  placed  at  either  end 
of  the  line,  or  at  any  intermediate  point ;  or  several  batteries 
may  be  introduced  at  different  points,  care  only  being  taken 
that  poles  of  the  same  kind  point  in  the  same  direction.  An 
Indicator  is  required  at  each  station,  for  the  purpose  of  receiv- 
ing messages,  whose  coils  are  directly  connected  with  the  line, 
and  form  a  part  of  it.  The  telegraphic  line,  therefore,  with  its 
batteries  and  instruments,  when  in  working  order  and  prepared 
to  transmit  messages,  constitutes  a  closed  circuit,  through  the 
whole  of  which  the  electrical  current  is  freely  circulating,  with 
the  electro-magnets  all  actuated  and  their  armatures  drawn 
down  tightly  upon  their  poles.  In  order  to  send  a  message,  the 
operator  commences  with  breaking  this  circuit  by  applying 
pressure  to  his  manipulator:  this  breaks  the  circuit  in  every 
instrument,  and  releases  the  armatures  throughout  the  entire 
line :  he  then  completes  the  circuit  for  a  longer  or  shorter  time, 
by  removing  the  pressure  from  his  manipulator,  and  thereby 
re-attracting  the  armature  of  his  Indicator,  an  effect  which  is 
also  repeated  in  every  instrument  upon  the  whole  line :  in  this 
munner  he  produces  a  telegraphic  letter,  and  by  a  succession  of 
similar  operations  forms  words  and  sentences,  which  are  of  ne- 
cessity repeated  in  every  instrument,  unless  the  line  is  purpo=e'y 
broken  and  the  current  sent  back  through  the  earth  at  some 
nearer  point.  The  Morse  system  is  almost  universally  used  in 
the  United  States,  and  more  extensively  in  Europe  than  any 
other.  In  England,  Cooke  and  Wheatstone's  single  or  double- 
needle  telegraph  is  commonly  employed.  The  ordinary  rate  of 
transmission  upon  the  Morse  instrument  is  about  1,000  words 
an  hour,  although  it  can  be  worked  as  high  as  2,700 :  upon  the 
Needle  instrument  it  is  about  900.  No  electric  telegraph  co  ild 
be  put  in'o  actual  operation  without  the  use  of  constant  batte- 
ries :  these  are  of  comparatively  late  invention,  that  of  Darnell's 
not  dating  farther  back  than  1836,  and  Grove's  about  a  year 
later.  All  previous  batteries  attained  their  maximum  intensity 
in  5  or  10  minutes,  and  were  altogether  unable  to  maintain  a 
steady  current,  continuing  unchanged  for  hours  and  days.  This 
affords  an  excellent  illustration  of  the  gradual  steps  by  which 
great  inventions  attain  perfection.  In  the  thirty  years  that  have 
elapsed  since  that  period,  the  telegraph  has  been  carried  from 
the  mo;t  eastern  extremity  of  Asia,  across  Europe  to  the 
mo>t  western  extremity  of  America,  and  at  no  distant  day  will 
completely  encircle  the  globe. 

410.    The  Transmission  of  Messages.     If  there  are  inter- 
mediate stations,  the  telegraphic  current,  in  passing  from  one 


396  TELEGRAPHIC    BATTERIES. 

extremity  of  the  line  to  the  other,  circulates  through  the  instru- 
ments of  all  the  stations,  and  every  message  is  repeated  simul- 
taneously by  every  Sounder,  even  by  those  which  are  far  in 
advance  of  the  station  to  which  the  message  is  sent.  When 
a  message  is  to  be  transmitted  from  one  end  of  the  line  to  the 
other,  or  to  an  intermediate  station,  the  operator  first  signals 
that  station  by  sounding  several  times  in  rapid  succession  the 
first  letter  of  its  name,  as  s,  for  Springfield,  if,  for  Boston,  in 
order  to  call  attention.  This  signal  is  repeated  at  every  station 
down  the  whole  line,  to  the  most  distant  extremity,  but  it  re- 
ceives no  notice  except  at  the  place  to  which  it  is  sent.  The 
operator  at  this  point  responds,  to  show  that  he  is  in  readiness, 
and  the  message  is  then  transmitted.  No  message  is  ever  sent, 
until  the  operator  at  the  proper  station  has  been  summoned. 
The  reply  is  transmitted  by  means  of  a  Manipulator,  as  already 
described,  and  this  reply  is  also  repeated  by  every  Sounder  on 
the  line,  both  behind'  as  well  as  in  advance  of  the  station  from 
which  it  started,  but  receives  no  attention  except  from  the  oper- 
ator who  has  been  summoned.  In  consequence  of  this  repetition 
of  messages  in  every  instrument,  it  is  easy  to  transmit  news  to 
many  points  on  the  same  line  simultaneously.  The  news  from 
New  York  City  for  the  morning  newspapers  in  New  England, 
is  transmitted  simultaneously  to  all,  by  one  operator  at  New 
York.  The  first  thing  done,  is  to  call  up  the  operators  at  the 
different  points,  by  striking  the  signals  appropriate  to  each  place 
in  succession,  and  when  it  has  been  ascertained  by  a  reply 
that  each  'is  at  his  post,  the  news  is  transmittt-d.  If  it  be  de- 
sired, however,  the  operator  who  is  summoned  at  any  station 
can  prevent  messages  from  going  further,  by  breaking  connec- 
tion with  the  line  beyond  him,  and  replying  by  his  own  battery 
and  local  ground  connection.  By  a  recent  improvement  the 
same  wire  can  be  used  to  transmit  messages  in  opposite  direc- 
tions, at  the  same  moment. 

411.  Telegraphic  Datteries.  Several  new  batteries  have 
been  constructed  within  a  few  years,  which  are  now  occasionally 
employed  for  telegraphic  purposes  instead  of  the  batteries 
already  described.  The  most  important  are  the  sulphate  of 
Mercury  battery,  Caillaud's  battery,  and  the  Sand  battery. 

The  sulphate  of  Mercury  battery,  Fig.  202,  No.  1,  is  gener- 
ally arranged  like  Bunsen's  battery,  but  the  dimensions  are 
less.  In  the  outside  cup,  in  place  of  water  acidulated  with 

410    Explain  the  transmission  of  messages  simultaneously  to  different  stations. 
411.  Describe  the  new  Telegraphic  batteries :  The  Sulphate  of  Mercury  battery. 


CAILLAUD'S  BATTERY. 


397 


Tke  Sulphate  of 
Mercury  Bailer  y. 


Caillaud^s 
Battery. 


Tke  Sand 
Battery. 


sulphuric  acid,  pure  water  is  used  or  else  water  containing  com- 
mon salt — chloride  of  sodium — in  solution  ;  in  the  porous  cup,  in 
place  of  nitric  acid,  a  solution  of  the  sulphate  of  mercury  is 
employed.  This  salt  not  being  very  soluble  is  mixed  with 
three  times  its  weight  of  water ;  the  water  is  then  decanted 
and  a  pasty  residue  left:  the  zinc  plates,  z,  and  the  carbon 
cylinders,  c,  having  been  put  into  their  places,  the  porous  cups 
are  then  filled  with  this  residuum,  and  afterwards  the  decanted 
liq  lid  is  poured  in.  The  action  of  the  battery  is  extremely 
s'mple:  the  water  in  the  outer  cell  being  decomposed,  the  oxy- 
gen unites  with  the  zinc  plate,  the  hydrogen  penetrate^  into 
the  po:  o  is  cup,  and  ds-oxidises  the  oxide  of  mercury,  setting 
free  metallic  mercury  and  sulphuric  acid ;  the  former  settles  at 
the  bot'om  of  the  porous  cup,  the  latter  passes  through  it,  and 
unites  with  the  oxide  of  zinc  in  the  outer  cup  to  form  sulphate 
of  zinc.  The  mercury  may  be  collected  and  used  to  prepare 
a  fresh  quantity  of  sulphate,  equal  in  amount  to  that  which 
has  been  decomposed.  This  battery  is  soon  exhausted  when 
used  continuously,  but  it  can  operate  during  three  or  four 
months  >co  as  to  furnish  interrupted  currents  like  those  which 
are  used  for  telegraphic  communication. 

412.  Caillaud's  Battery  This  battery  dispenses  with  por- 
ous cups  and  secures  the  separation  of  the  two  liquids  which  are 
required,  by  the  difference  in  their  density,  assisted  by  the  action 
of  the  current.  At  the  bottom  of  the  outside  cup,  v,  Fig.  202, 


412.  Describe  Caillaud's  battery. 


398  THE    EARTH   FORMS 

No.  2,  a  copper  plate  c,  is  deposited,  to  which  is  soldered  a 
copper  wire,  insulated  by  means  of  a  covering  of  gutta-percha,  i. 
On  the  top  of  this  plate  is  placed  a  layer  of  crystals  of  sulphate 
of  copper.  The  remainder  of  the  vessel  is  then  filled  with 
pure  water;  a  cylinder  of  zinc,  z,  is  then  introduced,  and  so 
placed  as  not  to  touch  the  sulphate  of  copper.  Thus  the  lower 
part  of  the  liquid  becomes  saturated  with  sulphate  of  copper, 
while  the  upper  part  remains  pure,  the  two  liquids  being  pre- 
vented from  mingling  by  a  difference  in  density,  and  also  by 
the  passage  of  the  current.  The  theory  of  this  battery  is  the 
same  as  that  of  Daniell,  §344 :  the  water  surrounding  the  zinc 
plate  is  decomposed,  the  oxygen  unites  with  the  zinc,  the  hydro- 
gen passes  into  the  sulphate  of  copper  solution,  and  de-oxi- 
dises the  oxide  of  copper  which  it  contains,  setting  free  metallic 
copper  and  sulphuric  acid :  the  former  attaches  ibelf  to  the  cop- 
per plate,  the  latter  moves  towards  the  zinc  plate  and  mvtes 
wi;h  the  oxide  of  zinc  to  form  sulphate  of  zinc :  the  direction 
of  the  current  is  from  z  to  c.  This  battery  is  extremely  eco- 
nomical, and  will  furnish  a  steady  current  for  several  months : 
a  little  water  must  be  added  from  time  to  time  to  replace  that 
lost  by  evaporation. 

413.  The  Sand  Battery.       In  this  battery,  which  is  ar- 
ranged  upon  the  same  plan  as  the  last,  Sand  is  employed  in 
order  to  render  the  separat'ori  of  the  liquids  more  complete. 
The   sulphate  of  copper  broken  into  coarse  rowder,  is  intro- 
duced first,  forming  a  layer  from  a  to  6,  Fig.  202,  No.  3  :  above 
it  is  placed  the  copper  plate  c,  with  its  insulated  wire  i :  on  the 
top  of  this,  a  layer  of  sand,  from  b  to  c:  then  the  zinc  plate,  z, 
and  the  remainder  is  filled  with  pure  water.     Sometimes,  the 
sulphate  of  copper  in  crystals  is  placed  on  the  top  of  the  copper 
plate,  and  the  sand  immediately  above  it.     These  new  batteries, 
however,  have   not   superseded  the    batteries  of   Daniell,  or 
Grove,  for  ordinary  telegraphic  use. 

414.  The  Earth  as  a  part  of  the   Telegraphic  circuit. 
One  of  the  most  remarkable  facts  connected  with  the  working 
of  the  telegraph,  is  the  extreme  facility  with  which  the   Earth 
conducts  the  electrical  current.     It  had  been  shown  by  Wat  i- on, 
in  the  last  century,  that  a  Leyden  jar  could   be   discharged 
through  a  circuit  one-half  of  which  consisted  of  moist  earth,  but 

cSteinhcil  was  the  first   to  employ  the  earth  to  act   the  part 
of  a  conducting  wire  in  a  telegraphic  circuit.     While  engaged 

413.  Describe  the  Sand  battery.—  414.  What  is  said  in  regard  to  the  earth  as  a  part 
of  the  telegraphic  circuit '!     Who  discovered  this  fact  ? 


,  A   PART    OF    THE  399 

in  1837,  upon  the  railroad  from  Nuremburg  to  Furtli,  in  ex- 
periments with  a  view  to  realize  a  hint  thrown  out  by  Gau-s, 
that  the  two  rails  of  a  railway  might  be  employed  as  conductors 
of  the  telegraphic  current  instead  of  wires,  and  finding  it  im- 
possible to  obtain  an  insulation  sufficiently  perfect  tor  tho 
current  to  reach  from  one  station  to  another,  he  was  led  to 
notice  the  great  conducting  power  of  the  earth,  and  to  conjec- 
ture that  it  might  be. employed  as  a  conductor  in  place  of  one 
of  the  telegraphic  wires.  His  experiments  were  crowned  with 
success,  and  he  then  introduced  into  telegraphy  one  of  its 
greatest  improvements,  both  in  regard  to  economy  from  the  sup- 
pression of  one  wire,  and  greatly  increased  facility  in  the  con- 
struction of  long  lines.  The  two  extremities  of  his  telegraphic 
lines  constructed  at  Munich  in  1839,  were  attached  to  two 
copper  plates,  which  were  buried  in  the  earth,  and  he  attrib- 
uted the  transmission  of  the  current  to  the  direct  conduction  of 
the  earth. 

In  1841  it  was  proved,  by  Wheatstone  and  Coolte  in  Eng- 
land, that  the  earth  may  be  employed  to  replace  one-half  the 
conducting  wire,  and  be  used  for  the  return  circuit ;  indeed 
they  found  that  the  same  battery  would  work  to  a  much  greater 
distance,  with  a  circuit  half  wire  and  half  ear  h,  than  when  al- 
together wire.  It  was  noticed  by  Bain  in  1841,  that  when  a 
plate  of  copper  was  buried  in  moist  earth,  and  connected  by  a 
wire  passing  through  a  galvanometer  with  a  similar  plate  of 
zinc  also  buried  in  the  earth  at  sone  distance  fro n  it,  that  a 
cuivent  of  considerable  intensity  was  generated  by  the  ac-ion 
of  the  zinc  on  the  moist  earth ;  and  on  increasing  the  size  of  the 
plafes,  not  only  were  powerful  electro-magnetic  effects  obtained, 
but  also  electro-type  deposits,  even  when  the  plates  were  more 
than  a  mile  apart.  The  battery  thus  formed  continued  to  wo  k 
for  a  great  length  of  time. 

In  1844,  Matteucci  caused  the  current  from  a  single  Bun- 
sen's  element  to  circulate  through  a  copper  wire  9,281  feet  in 
length,  and  through  a  portion  of  moist  earth  of  the  same  ex- 
tent, for  the  sake  of  comparison.  It  was  found  that  the  earth 
conducted  so  much  better  than  the  wire  that  its  resistance  must 
be  regarded  as  nothing,  and  that  the  resistance  of  copper  wire 
entering  into  the  earth  circuit,  was  less  than  that  offered  by 
the  same  wire  when  it  entered  alone  into  the  circuit.  It  was 
ascerjained  by  Breguet,  on  the  telegraph  line  between  Paris 

How  was  it  discovered?  What  did  Bain  discover?  Matteucci?  Why  is  the  con- 
duction of  the  earth  of  great  importance  in  telegraphy  ? 

17 


400  TELEGRAPHIC    CIRCUIT. 

i 

and  Rouen,  that  when  the  current  traversed  a  circuit  half 
metal  and  half  earth,  the  intensi:y  was  twice  as  great  as  when 
the  circuit  was  metallic  throughout — that  is,  a  chcuit  40  miles 
earth  and  40  miles  wire,  presented  no  more  resistance  than  a 
circuit  of  40  miles  wire,  the  earth  in  fact  offering  110  resist- 
ance at  all. 

This  is  a  fact  of  the  greatest  importance,  as  it  not  only 
permits  the  economy  of  a  one  line  wire,  but  a'so  renders  the  cur- 
rent twice  as  strong  as  it  would  be  if  returned  by  a  eecor.d 
metallic  wire.  Two  explanations  have  been  given  of  this 
non-resistance  of  the  earth ;  one,  that  as  the  conducting  power 
increases  in  proportion  to  the  area  of  a  section  of  the  conductor, 
the  earth  acting  as  a  conductor  with  an  infinite  area,  offers  a 
smaller  amount  of  resistance  than  the  metallic  part  of  the  cir- 
cuit ;  the  other,  that  the  earth  acts  as  an  immense  reservoir 
which  ab  orbs  all  the  positive  electricity  poured  into  it  on  the 
one  side,  and  the  negative  on  tha  other.  According  to  the  first 
theory,  between  two  stations  very  far  apart,  such  as  Washing- 
ton and  St.  Louis,  there  must  be  a  process  of  polarization  like 
that  described  in  §333,  Figs.  139,  140,  and  a  series  of  decom- 
positions and  recompositions  of  all  the  intervening  molecules 
of  water,  with  which  the  moist  earth  is  charged,  §365,  Fig.  103 : 
and  the  positive  electricity,  introduced  into  the  ground  at  Wash- 
ington, can  only  be  neutralized  by  the  negative  electricity  of  the 
same  battery,  which  has  gone  by  wire  to  St.  Louis,  and  thence 
back  through  the  earth  by  a  process  of  polarization  and  neu- 
tralization going  on  from  molecule  to  molecule,  of  the  interve- 
ning section  of  earth. 

According  to  the  second  theory,  the  earth,  on  account  of  its 
immense  size,  has  an  unlimited  capacity  for  electricity,  and  by 
absorbing  all  the  positive  and  negative  electricity  which  is  gen- 
erated by  the  battery,  produces  a  flow  of  the  electric  current  in 
the  wire :  or  the  earth  may  be  regarded  as  an  immense  battery, 
producing  electric  currents  that  are  passing  in  different  direc- 
tions, with  some  one  of  which  the  galvanic  current  forms  a 
connection,  making  it  part  of  the  telegraphic  circuit :  thus  the 
comparatively  feeble  current  which  traverses  the  line,  runs  into 
and  is  absorbed  by  the  mighty  current  of  the  subterraneous  bat- 
tery below,  and  is  hurried  on  with  a  greatly  accelerated  velocity. 
Objections  may  be  raised  in  reference  to  both  these  theories, 
but  the  former  is  more  in  accordance  with  the  principles  pre- 

State  the  two  theories  by  which  it  is  explained.    Which  is  preferred? 


THE  VELOCITY  OF  THE  TELEGRAPHIC  CURRENT.   401 

viously  laid  down,  in  regard  to  the  necessity  for  the  polarization 
of  the  entire  circuit  before  the  current  can  be  transmitted.  The 
fact  that  the  resistance  of  the  earth  to  the  passage  of  the  tele- 
graphic current  is  absolutely  null,  is  certain,  however  difficult 
may  be  its  explanation  ;  and  in  reference  to  its  influence  upon 
the  moral  and  social  welfare  of  men  by  dispensing  with  the 
necessity  of  a  second  return  wire  of  the  same  length  with  the 
first,  and  thus  greatly  facilitating  the  rapid  extension  of  the  tel- 
graph  over  the  whole  earth,  it  is  one  of  the  most  important 
discoveries  of  the  age. 

415.  The  velocity  of  the  Telegraphic  current.      It  has 
been  ascertained  by  an  ingenious  apparatus  devised  by  Wheat- 
stone,  that  the  velocity  of  statical  electricity  discharged  through 
a  copper  wire  half  a  mile  in  length,  is  288,000  miles  in  a  sec- 
ond, being  greater  than  the  velocity  of  light  in  the  ratio  of 
286  to  192.     In   regard  to  the  velocity  of  voltaic  electricity 
traversing  a  wire,  there  is  some  discrepancy  in  the  results  of 
experiments,  but  they  agree  in  showing  it  to  be  very  great. 
Thus,  according  to 

Prof.  Walker  of  the  U.  S.  Coast  Survey,  it  is  18,780  miles  per  second. 

Mitchell,        28,524  "  "  " 

Fizcau  and  Gounelle,  copper  wire,     ....  112,680  "  "  u 

"       "           "         iron  wire, 62,600  "  "  " 

Astronomers  of  Greenwich  and  Brussells,  cop-  j 

per  wire,  of  London  and  Brussells  Telegraph,  2,700  "  "  "       . 

Astronomers  of  Greenwich  and  Edinburgh, 
copper  wire,  of  London  and  Edinburgh  Tel- 
egraph,    7,600  "  "  "  1 

Gould, 15,890  "  "  " 

From  the  above  table  it  would  appear  that  the  velocity  of  vol- 
taic electricity  is  very  much  less  than  that  of  statical.  It  is 
probably  not  more  than  20,000  or  less  than  12,000  miles  per 
second.  Taking  Walker's  estimate  of  18,780  miles  per  second, 
it  would  require  1^  seconds  for  the  galvanic  current  to  traverse 
a  wire  extending  round  the  earth.  The  transmission  of  tele- 
graphic signals  must  therefore  be  practically  instantaneous. 

416.  The  Sub-marine  Telegraph.     In  the  sub-marine  tele- 
graph, copper  wires,  coated  with  gutta-percha,  are  wound  around 
a  central  rope  of  hemp,  in  such  a  manner  as  to  form  a  compound 
rope,  containing  several  strands  of  conducting  wire ;  the  whole 

415  What  is  the  velocity  of  statical  electricity  ?  Of  galvanic  electricity  ?  Giv«  the 
various  results.  What  is  th*  rate  of  transmission  of  the  telegraphic  current?  IIo\v 
much  time  is  required  for  its  circulation  around  the  globe? — 416.  Describe  the  sub- 
mariue  telegraph. 


402  THE  SUB-MARINE  TELEGRAPH. 

is  protected  by  a  flexible  metallic  covering  of  woven  wire,  and 
then  this  is  covered  with  an  exterior  covering  of  gutta-percha, 
or  tarred  hemp.  The  metallic  cable  is  coiled  in  the  hold  of  a 
steamer,  and  one  end  having  been  made  fast  to  the  shore,  and 
connected  with  a  land  telegraph,  the  rope  is  gradually  paid  out 
over  the  ship's  stern,  as  she  moves  steadily  forward,  and  from 
its  weight  sinks  to  the  bottom  of  the  sea.  When  the  opposite 
shore  is  reached,  the  end  of  the  cable  is  landed  and  connected 
with  a  land  telegraph.  In  working  a  telegraphic  line  consisting 
of  wires  covered  with  gutta-percha,  and  sunk  beneath  a  body 
of  water,  it  has  been  observed  that  when  the  cable  is  connected 
with  the  battery,  the  signal  is  not  instantaneously  transmitted 
to  the  distant  extremity ;  and  on  the  other  hand,  if  the  connection 
with  the  battery  be  broken,  there  is  not  an  instantaneous  cessa- 
tion of  electrical  action  at  the  distant  extremity.  There  is,  in 
short,  a  retardation,  and  subsequent  prolongation  of  the  electrical 
current.  This  is  owing  to  the  action  of  the  current  upon  the 
gutta-percha  insulator.  The  insulated  wire  constitutes,  in  fact, 
a  Ley  den  jar,  of  which  the  wire  forms  the  inside  surface,  the 
gutta-percha  constitutes  the  containing  vessel ;  the  external  iron 
wire,  or  the  water  of  the  ocean,  forms  the  outside  metallic 
covering.  The  time  lost  at  fir.-t,  is  that  which  is  consumed  in 
giving  the  gutta-percha  its  charge ;  being  a  non-conductor,  its 
particles  are  all  polarized  in  the  manner  represented  in  Figs. 
119, 124,  by  the  highly  electrified  wire.  If  the  wire  is  carrying 
a  current  ^positive  electricity,  the  gutta-percha  becomes  highly 
charged  with  a  proportionate  amount  of  negative  electricity,  and 
as  opposite  electricities  attract  each  other,  this  induced  negative 
electricity  reacts  upon  the  positive  electricity  with  which  the 
wire  is  charged,  exerts  an  attractive  influence  upon  it,  and  tends 
to  hold  it  fast,  and  to  check  the  flow  of  the  current  in  the  wire. 
If  the  wire  is  carrying  a  current  of  negative  electricity,  the 
effect  is  reversed,  the  gutta-percha  receives  by  induction  a 
charge  of  positive  electricity,  and  an  equal  retardation  is  pro- 
duced in  the  flow  of  the  current  through  the  wire.  On  the 
other  hand,  when  the  connection  with  the  battery  is  broken,  and 
the  current  of  electricity  carried  by  the  wire  is  stopped,  there 
is  a  gradual  cessation  of  the  polarized  state  in  the  gutta-percha, 
and  a  steady  decline  in  the  tension  of  the  induced  charge  which 
it  had  received,  and  this  allows  of  the  gradual  escape  of  the 
electricity,  which  it  had  held  back,  during  some  seconds  after  the 

Describe  the  retardation  and  prolongation  of  the  electrical  current.    Show  how  the 
Insulated  wire  constitutes  a  Leyden  jar. 


THE  ATLANTIC  TELEGRAPH  CABLE. 


403 


Fig.  203. 


connection  with  the  battery  has  ceased.  When  wires,  covered 
with  gutta-percha,  are  suspended  in  the  air,  no  such  polariza- 
tion takes  place,  on  account  of  the  non-conducting  power  of  the 
air,  which  do.js  not  allow  of  the  escape  of  the  repelled  ele> 
triclty,  and  the  wire  is  therefore  like  a  Leyden  jar,  who^e 
outside  surface  is  not  connected  with  the  earth,  §317. 

417.  The  Atlantic  Telegraph  Cable.  The  Atlantic  Tele- 
graph Cable,  which  was  successfully  laid  in  1866,  is  constructed 
of  a  core  of  7  copper  wires  imbedded  in 
gutta-percha,  and  protected  by  a  twisted 
strand  of  ten  steel  wires  covered  with 
tarred  hemp,  Fig.  203.  The  total 
diameter  of  the  cable  does  not  exceed 
l^j  inches.  Three  cups  only  of  the 
weakest  possible  form  of  the  galvanic 
battery  are  used,  each  consisting  of  a 
plate  of  copper,  at  the  bottom  of  a  glass 
jar  about  8  inches  in  depth,  filled  in 
with  saw  dust  dampened  with  pure 
water  without  the  u-e  of  "any  aciJ,  and 
a  piece  of  zinc  placed  upon  the  top  of 
it,  Fig.  204.  An  insulated  wire  is  at- 
tached to  each  copper  plate  leading  to  the  zinc  plate  in  the 

Fig-  204. 


Sftion  nf  th'  Atlantic 
Tdegrapk  Cattle. 


Tke  Atlantic  Telegraph  Battery. 

adjoining  jar.  A  few  pieces  of  sulphate  of  copper  are  dropped 
upon  the  copper  plate  previous  to  covering  it  with  saw  du>t. 
No  Indicator  is  employed  like  that  described  in  §407,  but  in- 
stead of  it  an  extremely  simple  instrument,  called  Thomson's 
Reflecting  Galvanometer,  Fig.  205. 

417.    Describe  the  Atlantic  cable,  and  the  battery  used  to  work  it. 


404 


THE    SIGNAL    INSTRUMENT. 


Fig.  205. 


Thomson's  Effecting  Galvanometer, 
in  section. 


It  consists  of  a  coil  of 
wound  wire,  seen  in  section, 
at  c,  having  a  very  small 
magnet,  m,  suspended  with- 
in it  by  a  single  filament  of 
silk ;    on  the  front  of  this 
magnet  is  fastened  a  small 
mirror,  n,  and  the  magnet 
and  mirror  are  made  to  as- 
sume a   fixed  position,   at 
right  angles  to  the  axis  of 
the  coil  by  the  permanent 
liorse-shoe  magnet,  s  N. — 
A  D,  is   a  screen,  at  a  dis- 
tance of   about  26  inches 
from  the  magnet,  having  a 
vertical    slit,    cut    directly 
opposite  to  the  mirror,  n, 
and    behind     this    slit    is 
placed    a    lamp,    B.      The 
screen  is  graduated  on  each 
side  of  the  slit,  each  divis- 
ion being  about  4^1  h  of  an 
inch  in  length :  L  is  a  lens 
by  which  the  light  proceed- 
ing from   the  lamp  is  con- 
centrated upon  the  mirror. 
The  extremities  of  the  coil, 
C,  are  connected  with  the 
telegraphic  wire  in  such  a 
manner    that   the    current 
may  at  pleasure  be  made  to 
circulate    through    it.     An 
electrical    current,  passing 
through  the  coil,  however 
sligi.t,  tends  to  counteract 
the  attractive  influence  of 
the  fixed  magnet,  s  N,  and 
to  turn  the  magnet,  m,  into 
a  position  at    right  angles 
to  its  former  po;-ition,  and 
parallel  to  the  axis  of  the 
coil.     As  long  as  no  tele- 
graphic current  passes 


THOMSON'S  REFLECTING  GALVANOMETER.  405 

through  the  coil,  the  magnet,  m,  remains  undisturbed  in  its 
fixed  portion,  and  the  light  proceeding  from  the  lamp,  B, 
passing  through  the  vertical  slit,  and  falling  upon  the  mirror, 
71,  is  reflected  back  upon  the  same  line  and  returns  through 
the  slit  to  the  lamp,  but  the  instant  the  current  passes,  the  mag- 
net is  made  to  deviate  from  its  fixed  position  either  to  the  right 
or  to  the  left,  and  a  spot  of  light  is  reflected  to  the  right  or  left 
of  the  slit,  and  made  to  fall  upon  the  graduated  scale,  A  D. 
If  the  positive  current  turn  it  to  the  right,  and  throw  the 
reflected  spot  of  light  to  the  right  of  the  vertical  slit,  a  neg- 
ative current  will  turn  it  to  the  left,  and  throw  the  reflected 
spot  to  the  left  of  the  same  slit.  The  telegraphic  operator 
has  the  power  of  transmitting  a  positive  or  negative  current 
at  pleasure,  by  means  of  the  key,  M,  in  Fig.  207  :  when  it  is 
moved  so  as  to  touch  jt>,  a  positive  current  is  transmitted ; 
when  it  is  moved  so  as  to  touch  n,  a  negative  current  is  trans- 
mitted. Thus  the  spot  of  reflected  light  is  easily  thrown  either 
to  the  right  or  the  left  on  the  graduated  scale,  A  D.  When 
thrown  to  the  right,  a  dot  is  indicated  ;  when  thrown  to  the  left,  a 
dash ;  and  fro  n  these  tha  characters  of  Morse's  alphabet,  §408 
are  readily  produced.  By  this  very  simple  apparatus,  the  longest 
messages  can  be  sent  from  one  side  of  the  Atlantic  to  the  other. 
The  observer  who  receives  the  message  sits  upon  the  side  of  s  N 
opposite  to  B,  and  with  the  instrument,  is  placed  in  a  dark  room. 
418.  Thomson's  Reflecting-  Galvanometer.  The  actual 
form  of  the  Reflecting  Galvanometer  employed  may  be  seen  in 
Fig.  206  :  w  represents  a  cylindrical  box  containing  the  coil  of 
wire  having  the  magnet  and  mirror  suspended  in  it  by  a  few 
fibres  of  unspun  silk ;  in  the  front  of  the  box  at  the  opening 
of  the  coil,  is  placed  a  small  lens,  /:  the  coil  with  its  con- 
necting wires  is  mounted  upon  a  stand,  and  provided  with 
leveling  screws.  Upon  a  perpendicular  rod  mounted  upon  the 
top  of  this  box,  slides  the  horse-shoe  magnet,  m,  by  which, 
when  brought  down  upon  the  sides  of  the  box,  the  operator  is 
enabled  to  give  a  fixed  position  to  the  internal  magnet  carrying 
the  mirror.  At  R,  is  seen  the  screen,  bearing  the  graduated 
scale ;  at  L,  the  lamp,  placed  behind  the  screen,  and  at  s,  the 
vertical  slit,  through  which  the  light  passes  to  the  lens,  Z,  by 
which  it  is  concentrated  upon  the  mirror,  and  from  this  reflected 
upon  the  scale,  R.  As  a  very  slight  angular  deviation  of  the 
magnet  causes  the  spot  of  light  to  traverse  the  whole  scale,  this 

Describe  the  Signal  instrument,  Fig.  205.  How  is  the  passage  of  the  current  mani- 
fested .  How  does  the  reflected  spot  of  light  communicate  intelligence?  Why  does  the 
observer  sit  in  a  dark  room  ?•— 418.  Describe  the  actual  form  of  the  Signal  instrument. 


496 


THE  ARRANGEMENT  OF  THE  CABLE. 


instrument  becomes  an  extremely  delicate  indicator  of  the  pas- 
sage  of  the  current  through  the  cable.  The  observer  sits  behind 
the  box,  w,  in  a  darkened  room.  The  coil,  mirror  and  magnet, 
are  seen  in  section,  separately  on  the  right  of  the  engraving. 

Fig.  206. 


The  Atlantic  Telegraph  Signal  Instrument. 

•9:19.  The  actual  arrangement  of  the  Cable.  The  actual 
arrangement  of  the  battery  and  cable  is  represented  in  Fig. 
207 :  B  and  B',  represent  the  two  batteries,  and  E,  the  plate 
buried  in  the  ground  on  one  side  of  the  ocean ;  M,  is  the 
key  for  sending  at  pleasure  either  a  positive  or  negative  cur- 
rent ;  A,  the  point  at  which  the  cable  enters  the  sea ;  G,  the 
signal  galvanometer;  p,  the  pTate  buried  in  the  earth  on 
the  other  side  of  the  ocean.  The  current  circulates  from  one 
pole  of  the  battery  through  A  to  G,  thence  to  the  plate  F,  and 
from  this  returning  through  the  or'ean  to  the  plate  E,  finally 
reaches  the  opposite  pole  of  the  battery  to  that  from  which  it 
started.  To  use  the  cab^e  advantageously,  a  uniform  current 
of  positive  or  negative  electricity  must  not  be  employed,  but 
the  current  should  be  often  reversed;  this  is  accomplished,  in 
the  instrument  above  described,  by  the  constant  alterations  re- 
quired to  produce  the  dots  and  dashes,  as  already  described. 

419.  Describe  the  actual  arrangement  of  the  Cable. 


THE    RATE    OF    TRANSMISSION. 


407 


Fig.  207 


Transmission  of  the  current  across  the  Ocean. 


420.  The  rate  of  trans- 
mission. The  signal  is 
transmitted  instantly,  but 
a  slight  delay  of  perhaps 
gthsofa  second  is  expe- 
rienced in  freeing  the  ca- 
ble. The  rate  of  transmis- 
sion is  fifteen  words  or 
seventy-five  letters  per 
minute,  but  twenty  words 
can  be  sent  quite  easily. 
There  is  no  doubt  that 
with  the  various  land 
lines  free  from  other  du- 
ty, a  despatch  of  twenty 
words  could  readily  be 
transmitted  from  London 
to  New  York,  or  vice 
versa,  in  the  time  requir- 
ed to  write  it  over  four 
or  five  times  ;  or  in  other 
words,  it  is  possible  to 
send  it  the  entire  distance 
in  five  minutes,  every 
thing  being  in  readiness 
for  it.  The  difference  of 
time  being  greatly  in  fa- 
vor of  New  York,  des- 
patches often  reach  New 
York  dated  at  a  later  hour 
than  that  at  which  they 
arrive.  The  news  pub- 
lished in  the  New  York 
afternoon  newspapers, 
leaves  London  often  at  3 
p.  M.  of  the  same  day. 
On  one  occasion  a  des- 
patch was  received  at 
New  York  at  about  1 1 .30 
p.  M.,  dated  London  the 
following  day.  On  an- 
other occasion  a  despatch 
from  Rome  reached  New 


408  HISTORY    OF    THE    ATLANTIC    CABLE. 

York  at  8  A.  M.  on  the  day  of  its  date,  was  placed  in  a  "Western 
city  at  8  A.  M.,  and  the  reply  which  passed  New  York  eastward 
about  1 1 .30  A.  M.,  doubtless  reached  Rome  in  the  evening  of 
the  same  day.  On  one  occasion  a  despatch  was  sent  from 
London  to  Washington  in  nine  minutes  and  thirty  seconds,  and 
was  received  in  Washington  four  hours  fifty-eight  minutes  and 
thirty  seconds  in  advance  of  the  hour  of  its  leaving  London. 
On  the  morning  of  Feb.  1st,  1868,  the  wires  of  the  Western 
Union  Telegraph  Company  from  San  Francisco  to  Plaister  Cove, 
Cape  Breton,  and  the  wires  of  the  New  York,  Newfoundland, 
and  London  Telegraph  Company  from  Plaister  Cove  to  Heart's 
Content,  were  connected,  and  a  brisk  conversation  commenced 
between  these  two  continental  extremes.  Compliments  were 
then  exchanged  betwen  San  Francisco  and  Valentia,  Ireland, 
when  the  latter  announced  that  a  message  was  just  then  being 
received  from  London  direct.  This  was  said  at  7.20  A.  M., 
Valentia  time,  Feb.  1 :  at  7.31  A.  M.,  Valentia  time,  the  London 
message  was  started  from  Valentia  for  San  Francisco ;  passed 
through  New  York  at  2.35  A.  M.,  New  York  time ;  was  re- 
ceived in  San  Francisco  at  11.21  P.  M.,Jan.  31,  San  Francisco 
time,  and  was  at  once  acknowledged — the  whole  process  oc- 
cupying two  minutes  actual  time,  and  the  distance  traversed 
about  14,000  miles!  Immediately  after  the  transmission  of 
the  message  referred  to,  the  operator  at  San  Francisco  sent  an 
eighty-word  message  to  Heart's  Content  in  three  minutes,  which 
the  operator  at  Heart's  Content  repeated  back  in  two  minutes 
and  fifty  seconds :  distance  about  5,000  miles !  Notwithstand- 
ing the  great  length  of  ihe  Cable  no  supplemental  battery  is 
required,  because  the  whole  force  of  the  current  is  transmitted, 
none  being  lost  as  in  the  case  of  the  Land  Telegraph  through 
imperfect  insulation. 

421.  History  of  the  Atlantic  Telegraph.  The  construc- 
tion of  the  Atlantic  Telegraph  is  considered  one  of  the  most 
remarkable  scientific  achievements  of  the  present  Century. 
The  first  and  second  attempts  at  laying  the  cable  in  1857  and 
1858  were  unsuccessful.  The  third  attempt  somewhat  later  in 
the  year  1858  succeeded,  and  telegraphic  communi  ation  across 
the  Atlantic  was  maintained  from  Aug.  6th  to  Sept.  1st,  two 
hundred  and  seventy-one  messages  having  been  transmitted 
from  Newfoundland  to  Valentia,  and  one  hundred  and  twerity- 

420.  State  the  rate  of  transmission.  Mention  instances  of  the  rapid  transmission  of 
despatches.  Explain  how  a  message  from  London  may  be  received  at  ^ew  York  the  day 
before  it  is  sent. — 421.  Give  the  history  of  the  Atlantic  Cable. 


MOTIOX    PRODUCED 


409 


nine  from  Va'entia  to  Newfoundland.  On  August  31st  two 
important  messages  were  sent  to  the  British  government  from 
Newfoundland,  but  the  next  day  communication  ceased,  and 
no  efforts  to  reestablish  it  proved  of  any  avail.  In  1865 
the  enterprise  was  renewed  with  an  improved  cable,  which  was 
successfully  laid  by  the  Great  Eastern  about  half  way  across 
the  Atlantic,  when  it  parted,  and  all  efforts  at  recovery  failed. 
In  1866  the  undertaking  was  renewed  with  a  new  cable,  which 
was  successfully  landed  in  Newfoundland  July  27th.  The 
ships  then  returned  to  mid-ocean  tor  the  purpose  of  finding  and 
raising  the  lost  cable  of  the  previous  year.  It  was  found  with- 
out difficulty,  and  after  many  unsuccessful  attempts,  was  fin  d  y 
raised,  spliced  to  the  remaining  portion,  and  the  whole  Ian  led 
at  Newfoundland,  Sept.  7th.  The  successful  laying  of  these 
cables  is  due  to  Mr.  C.  W.  Field. 

422.  Application  of  El2ctro-T!YIa<jnetism  to  the  produc- 
tion of  motion.  Various  applicat  ons  h  ive  been  made  of  the 
galvanic  current  to  the  production 
of  motion.  They  all  depend  upon 
the  instantaneous  production  and 
destruction  of  force  by  establishing 
and  breaking  the  connect'on  be- 
tween the  Battery  and  an  Electro- 
magnet. One  of  the  simplest  in- 
struments for  this  purpose  is  repre- 
sented in  Fig.  208.  It  represents 
an  electro-magnet  wound  with  cov- 
ered wire,  and  supported  vertically 
upon  a  stand :  w  is  a  brass  wheel, 
carrying  upon  its  circumference 
three  armatures  of  soft  iron,  placed 
at  right  angles  to  the  p'ane  of  the 
wheel.  At  B,  on  the  shaft  of  the 
wheel,  is  a  break  piece,  consisting  of 
a  small  metallic  disc,  from  which 
project  in  a  lateral  direction  three 
iron  pins  corresponding  with  the 
three  iron  armatures.  The  battery 
current  entering  at  the  b!nding  cup, 
p,  divides  info  two  branches  and  as- 
cends each  of  the  legs  of  the  electro- 
magnet, then  descending,  the  two 


Motion  produced  by 
Electro-magnetism. 


422.  On  what  does  the  production  of  motioii  by  electro-magnetism  depend  ?    Describe 
Fig.  208. 


410  BY    ELECTRO-MAGNETISM. 

branches  unite  and  ascend  by  the  single  external  wire,  B,  to 
the  break-piece  :  thence  it  passes,  whenever  one  of  the  three 
iron  pins  is  in  contact  with  the  silver  spring  in  which  the  wire 
terminates,  into  the  shaft  of  the  wheel,  and  so  by  the  brass 
supports,  s  s,  into  the  iron  cores  of  the  electro-magnet,  finding 
its  way,  at  M,  into  the  binding  cup,  n,  where  it  makes  its  final 
exit.  The  silver  spring  is  arranged  in  such  a  way  as  to  come 
into  contact  with  each  iron  pin  at  the  moment  when  the  corres- 
ponding armature  is  within  a  quarter-revolution  of  the  po'es 
of  the  electro  magnet,  and  to  cease  its  contact  the  ins! ant  ea<  h 
armature  is  brought  directly  over  the  two  electro  -magi;  etic 
poles.  As  soon  as  contact  between  the  pin  and  spring  takes 
place,  the  current  passes,  the  electro-magnet  is  excited,  and  the 
armature  is  attracted  forcibly  towards  the  poles  of  the  magnet : 
when  it  reaches  them,  contact  is  broken,  the  current  cea  es,  and 
the  electro-magnet  lo.es  its  power:  the  wheel  however,  continues 
its  revolution,  in  consequence  of  the  momentum  which  it  has 
acquired,  until  the  pin  of  the  second  armature  comes  into  contact 
with  the  break-piece,  when  the  electro-magnet  aga;n  becomes 
charged,  the  second  armature  is  attracted,  contact  is  again 
broken,  and  thus  the  process  goes  on.  By  these  successive 
attractions  a  rapid  rotary  movement  is  imparted  to  the  wheel, 
which  continues  as  long  as  the  current  circulates.  This  is  one 
of  the  most  simple  forms  of  an  electro-magnetic  rotary  ma- 
chine. There  are  others  of  a  much  more  complicated  con- 
struction, and  possessed  of  sufficient  power  to  be  used  in  tjie 
movement  of  machinery. 

423.  Elcctro-BZotcr  of  3JH.  Troincnt.  Fig.  209  represents  a 
machine  constructed  by  M.  Froment,  at  Paris,  lor  the  application 
of  galvanic  electricity  as  a  motive  force  in  place  of  steam.  The 
principle  is  the  same  as  in  the  preceding  instrument,  and  its  ac- 
tion depends  upon  the  instantaneous  generation  and  destruction 
of  motive  power  by  establishing  and  breaking  the  circulation  of 
the  current.  It  consists  of  four  powerful  electro-magnets,  A,  B, 
c,  D,  fa  tened  upon  an  iron  frame,  x.  Between  these  electro- 
magnets are  two  iron  wheels,  on  the  same  horizontal  axis,  carry- 
ing eight  Foft  iron  armatures,  M,  M,  mounted  on  their  circumfer- 
ence parallel  to  the  axis.  The  current  from  the  battery  enters 
at  K,  a-cends  the  wire,  E,  and  reaches  the  metallic  arc,  o,  which 
transmits  the  current  successively  into  each  pair  of  electro- 
magnets. The  current  is  broken  in  each  pair,  and  their  mag- 

423.    Describe  the  Electro-motor  of  M.  Froment. 


THE    ELECTKO-MOTOR    OF    M.    FKOMENT. 
Fig.  209. 


411 


Fromenl's  Eiectro-j.ij.uior  for  driving  machinery. 


netism  d°stroyed  just  as  each  armature  comes  opposite  to  their 
poles,  and  is  made  to  circulate  aga  n  and  to  re-establish  their 
magnetism  at  the  moment  when  each  armature  has  passed  one- 
half  the  distance  which  separates  each  pair  fron  the  pair 
immediately  following.  This  adjustment  is  effected,  and  tin 
proper  connections  established  and  broken  at  the  required  mo- 
ment, by  means  of  cogs  arranged  upon  the  arc,  o.  The  cur- 
rent finally  makes  its  exit,  and  returns  to  the  battery  by  the 
wire,  H.  In  thi<  manner,  the  armntures,  being  attracted  in  suc- 
cession by  the  four  pairs  of  electro-magnets,  the  wheels  to  which 
they  are  attached  acquire  a  rapid  rotary  motion,  and  this,  by 
the  wheel,  P,  and  an  endless  band,  is  transmitted  to  any  ma- 


412         THE  ELECTRO-MOTOR  OF  M.  JACOBY. 

chine,  a  grinding  mill  for  example,  which  it  is  desired  to  move. 
The  machine  employed  in  the  workshop  of  M.  Froment  is  of 
about  one-horse  power. 

424.  The  Electro-motor  of  IKI.  Jacoby.    Electro-magnetic 
engines  of  much  greater  power  have  been  constructed.    In  1838, 
M.  Jacoby,  at  St.  Petersburg,  built  an  electro-magnetic  eng'ne 
of  sufficient  power  to  propel  a  boat  containing  twelve  persons, 
upon  the  river  Neva.     The  vessel  was  a  ten-oared  shallop,  pro- 
vided with  paddle-wheels,  to  which   motion  was  given  by  the 
electro-magnetic  engine.     The  boat  was  28  feet  long,  1{  wide, 
and  drew  2f  feet  of  water.     During  a  v 03  age  which  lasted  sev- 
eral days  the  Vessel  went  at   the  rate  of  four  miles  an  hour. 
In   1 839,  a  second  experiment  was  tried  in  the  same  boat,  the 
machine  being  worked  by  a  Grove's  battery  of  64  platinum 
plates,  each  having  36  square  inches  of  surface.     The  boat, 
with  a  party  of  fourteen  persons  on  board,  went  against  the 
stream  at  the  rate  of  three  miles  an  hour. 

425.  Electro-Magnetic   Locomotives.       About    1840,    an 
electro-magnetic  railroad  engine  was  constructed  by  Mr.  David- 
son, in  Scotland,  and  tried  by  the  inventor  on  the  Edinbmgh  and 
Glasgow  railroad;  it  weighed,  with  its  carnages,  batteries,  &c., 
five  tons,  but  when  put  in  motion  it  traveled  only  four  m  les  an 
hour,  exerting  a  power  less  than  that  of  a  single  man.     The 
arrangement  of  this  engine  was  not  unlike  that  exhibited  in  the 
machine,  Fig.  208,  the  chief  difference  being  that  two  e'ectro- 
magnets  were  employed  instead  of  one,  and  arranged  in  such  a 
manner  as  to  operate  directly  upon  ihe  shaft  of  the  engine,  the 
magnetism  of  the   electro-magnets  being  perpetually  induced 
and  destroyed  at  the  proper  moment  by  making  and  breaking 
connection  with  the  battery. 

426.  Page's  Electro-Magnetic  Locomotive.       Some  very 
efficient  electro-motors  have  been  constructed  by  our  country- 
man, Dr.  Page.     With  an  electro-magnetic  locomotive  provided 
with  two  of  these  machines,   rated  at  four-horse  power  each, 
actuated  by  a  Grove's  battery  of  one  hundred  pairs,  a  speed  at 
the  rate  of  nineteen  miles  an  hour  upon  a  level  grade  was  at- 
tained :  the  car  weighed  eleven  tons,  and  carried  fourteen  passen- 
gers.    The  engine  employed  was  the  axial  engine.     In  all  other 
engines  the  motion  is  produced  by  electro-magnets  of  soil  iron, 
which  are  alternately  magnetized  and  de-magnetized,  as  in  Fig. 

424.   Describe  the  Electro-motor  of  M.  Jacoby. — 425.  Describe  Davidson's   Electro- 
magnetic Locomotive.— 426.  Describe  Page's  Electro-magnetic  Locomotive. 


PAGE'S  ELECTRO-MAGNETIC  LOCOMOTIVE.  413 

208,  and  in  Froment's  electro-motor,  Fig.  209.  In  this  machine 
the  electro-magnets  are  dispensed  with,  and  a  long  hollow  helix 
is  employed,  consisting  of  several  distinct  helices,  placed  o:ie 
above  another,  so  as  to  make  a  hollow  tube,  each  having  inde- 
pendent connections  with  the  battery,  insulated  from  each 
other,  and  arranged  in  such  a  way  that  each  helix  can  be  mag- 
netized and  de-magnetized  in  succession. — It  is  well  known  that 
a  helix  of  wound  wire  itself  becomes  magnetic,  and  possesses 
as  much  attractive  power  as  the  iron  armature  placed  witlrn 
it,  Fig.  184,  p.  363.  If  such  a  helix,  mounted  in  a  vertical 
position  in  such  a  way  that  an  iron  rod  can  be  introduced  into 
it  from  below,  be  connected  with  a  battery,  the  iron  rol  wi.l 
be  at  once  drawn  up  into  it  and  be  sustained  oscillating  in 
its  axis,  even  though  it  may  weigh  many  pounds.  On  one 
occasion,  by  means  of  a  huge  helix,  a  weight  of  2,0  )0  Ibs. 
was  raised  five  inches  from  the  floor,  and  caused  to  vibrate 
for  an  inch  up  and  down  by  the  pressure  of  the  finger.  The 
battery  used  was  fifty  pairs  of  Grove's,  with  platinum  plates 
twelve  inches  square,  ten  inches  immersed.  This  is  called  the 
axial  force  of  magnetism.  If  the  iron  rod  be  suspended  over 
the  opening  of  such  a  helix,  as  a  b,  in  Fig.  210,  insteal  of 
under,  it  will  be  drawn  down  with  equal 
force  as  soon  as  the  wires,  /?,  n,  are  conn  -cted 
with  the  battery. — In  the  interior  of  this 
compound  helix  a  powerful  steel  magnet  is 
suspended  with  its  upper  end  upon  a  level 
with  the  top  of  the  helix,  and  fastened  to  a 
connecting  rod  attached  to  a  crank  and  axle. 
As  soon  as  the  helix  opposite  its  lower  end 
is  magnetized,  a  powerful  attraction  is  exerted 
Tke  axmi  electro-  upon  the  magnet,  tending  to  draw  it  down- 

magnetic  Force.  -,  .,     j  i        •-      i  » 

wards:  as  it  descends,  it  de-magnetizes,  by 
means  of  a  proper  break-piece,  every  helix  that  it  passes  an  I 
leaves  behind  it,  while  it  magnetizes  in  succession  every  helix 
in  advance  of  it.  AVhen  it  reaches  the  bottom  of  the  compound 
helix  the  process  is  reversed,  every  helix  above  it  is  succes- 
sively magnetized,  while  every  helix  that  it  passes  is  immedi- 
ately de -magnetized.  Thus  the  magnet  is  made  to  rise  again 
to  the  upper  portion  of  the  compound  helix,  and  a  reciprocating 
motion  is  produced  which  is  imparted  to  the  crank  and  axle. 
An  axial  engine  of  this  description  was  exhibited  at  the  Smith- 

W'nt  JH  the  fi.na'  force  of  magnum?    What  extraordinary  effects  are  produced  by 
this  force >     Describe  Pugc'd  axial  eugiue. 


412        THE  ELECTRO-MOTOR  OF  M.  JACOBY. 

chine,  a  grinding  mill  for  example,  which  it  is  desired  to  move. 
The  machine  employed  in  the  workshop  of  M.  Froment  is  of 
about  one-horse  power. 

424.  The  Electro-lKotor  of  XVX.  Jacoby.    Electro-magnetic 
engines  of  much  greater  power  have  been  constructed.    In  1838, 
M.  Jacoby,  at  St.  Petersburg,  built  an  electro- magnetic  eng'ne 
of  sufficient  power  to  propel  a  boat  containing  twelve  persons, 
upon  the  river  Neva.     The  vessel  was  a  ten-oared  shallop,  pro- 
vided with  paddle-wheels,  to  which   motion  was  given  by  the 
electro-magnetic  engine.     The  boat  was  28  feet  long,  7^  wide, 
and  drew  2f  feet  of  water.     During  a  vo\  age  which  lasted  sev- 
eral days  the  Vessel  went  at   the  rate  of  four  miles  an  hour. 
In   1839,  a  second  experiment  was  tried  in  the  same  boat,  the 
machine  being  worked  by  a  Grove's  battery  of  64  platinum 
plates,  each  having  36  square  inches  of  surface.     The  boat, 
with  a  party  of  fourteen  persons  on  board,  went  against  the 
stream  at  the  rate  of  three  miles  an  hour. 

425.  Electro- Magnetic   Locomotives.       About   1840,    an 
electro-magnetic  railroad  engine  was  constructed  by  Mr.  David- 
son, in  Scotland,  and  tried  by  the  inventor  on  the  Edinbuigh  and 
Glasgow  railroad;  it  weighed,  with  its  carriages,  batteries,  &c., 
five  tons,  but  when  put  in  motion  it  traveled  only  four  m'les  an 
hour,  exerting  a  power  less  than  that  of  a  single  man.     The 
arrangement  of  this  engine  was  not  unlike  that  exhibited  in  the 
machine,  Fig.  208,  the  chief  difference  being  that  two  e'ectro- 
magnets  were  employed  instead  of  one,  and  arranged  in  such  a 
manner  as  to  operate  directly  upon  the  shaft  of  the  engine,  the 
magnetism  of  the   electro-magnets  being  perpetually  induced 
and  destroyed  at  the  proper  moment  by  making  and  breaking 
connection  with  the  battery. 

426.  Page's  Electro-Magnetic  Locomotive.       Some  very 
efficient  electro-motors  have  been  constructed  by  our  country- 
man, Dr.  Page.     With  an  electro-magnetic  locomotive  provided 
with  two  of  these  machines,   rated  at  four-horee  power  each, 
actuated  by  a  Grove's  battery  of  one  hundred  pairs,  a  speed  at 
the  rate  of  nineteen  miles  an  hour  upon  a  level  grade  was  at- 
tained :  the  car  weighed  eleven  tons,  and  carried  fourteen  passen- 
gers.    The  engine  employed  was  the  axial  engine.     In  all  other 
engines  the  motion  is  produced  by  electro-mr.gnets  of  Foil  iron, 
which  are  alternately  magnetized  and  de-magnetized,  as  in  Fig. 

424.   Describe  the  Electro-motor  of  M.  Jacoby.— 425.  Describe  Davidson's   Electro- 
maguetic  Locomotive.— 426.  Describe  Page's  Electro-magnetic  Locomotive. 


PAGE'S  ELECTRO-MAGNETIC  LOCOMOTIVE.  413 

208,  and  in  Froment's  electro-motor,  Fig.  209.  In  this  machine 
the  electro-magnets  are  dispensed  with,  and  a  long  hollow  helix 
is  employed,  consisting  of  several  distinct  helices,  placed  o:ie 
abave  another,  so  as  to  make  a  hollow  tube,  each  having  inde- 
pendent connections  with  the  battery,  insulated  from  each 
other,  and  arranged  in  such  a  way  that  each  helix  can  be  mag- 
netized and  de-magnetized  in  succession. — It  is  well  known  that 
a  helix  of  wound  wire  itself  becomes  magnetic,  and  possesses 
as  much  attractive  power  as  the  iron  armature  placed  witlrn 
it,  Fig.  184,  p.  363.  If  such  a  helix,  mounted  in  a  vertical 
position  in  such  a  way  that  an  iron  rod  can  be  introduced  into 
it  from  below,  be  connected  with  a  battery,  the  iron  rol  wi.l 
be  at  once  drawn  up  into  it  and  be  sustained  oscillating  in 
its  axis,  even  though  it  may  weigh  many  pounds.  On  one 
occasion,  by  means  of  a  huge  helix,  a  weight  of  2,0  >0  Ibs. 
was  raised  five  inches  from  the  floor,  and  caused  to  vibrate 
for  an  inch  up  and  down  by  the  pressure  of  the  finger.  The 
battery  used  was  fifty  pairs  of  Grove's,  with  platinum  plates 
twelve  inches  square,  ten  inches  immersed.  This  is  called  the 
axial  force  of  magnetism.  If  the  iron  rod  be  suspended  over 
the  opening  of  such  a  helix,  as  a  b,  in  Fig.  210,  instea  1  of 
under,  it  will  be  drawn  down  with  equal 

i£.  210.  f  .  , 

iorce  as  soon  as  the  wires,  />,  n,  are  conn  -cted 
with  the  battery. — In  the  interior  of  this 
compound  helix  a  powerful  steel  magnet  is 
suspended  with  its  upper  end  upon  a  level 
with  the  top  of  the  helix,  and  fastened  to  a 
connecting  rod  attached  to  a  crank  and  axle. 
As  soon  as  the  helix  opposite  its  lower  end 
is  magnetized,  a  powerful  attraction  is  exerted 
The.  axmi  electro-  upon  the  magnet,  tending  to  draw  it  down- 
wards: as  it  descends,  it  de-magnetizes,  by 
means  of  a  proper  break-piece,  every  helix  that  it  passes  an  I 
leaves  behind  it,  while  it  magnetizes  in  succession  every  helix 
in  advance  of  it.  When  it  reaches  the  bottom  of  the  compound 
helix  the  process  is  reversed,  every  helix  above  it  is  succes- 
sively magnetized,  while  every  helix  that  it  passes  is  immedi- 
ately de -magnetized.  Thus  the  magnet  is  made  to  rise  again 
to  the  upper  portion  of  the  compound  helix,  and  a  reciprocating 
motion  is  produced  which  is  imparted  to  the  crank  and  axle. 
An  axial  engine  of  this  description  was  exhibited  at  the  Smith- 

W'vtt  5s  the  n.r>a>  force  of  magnetism?     What  extraordinary  effects  are  produced  by 
this  force  ?    Describe  rage's  axial  eugiue. 


414  THE    COST   OF   ELECTRO-MAGNETIC 

sonian  Institute  of  four  or  five  horse-power,  the  battery  of 
which  was  contained  within  the  space  of  three  cubic  feet ;  it 
wa>  a  reciprocating  engine  of  two  feet  stroke,  and  the  whole, 
including  the  battery,  weighed  about  one  ton. 

427.  Stewart's  Electro-HSotor.  Recently  an  electro-motor 
has  been  constructed  by  Mr.  Stewart,  in  New  York,  in  which 
a  central  axis  about  tiiree  feet  in  length,  is  surrounded  by  a 
series  of  electro-magnets  so  placed  that  magnetic  action  is 
maintained  continually,  and  without  intermission.  The  magnets 
are  only  magnetized  twice  in  one  revolution,  instead  of  many 
times  as  in  most  oUier  motors  that  have  been  constructed ;  it  ij 
claimed  that  much  greater  power  is  obtained,  arid  at  far  less 
expense  than  any  other  machine  that  has  been  invented.  The 
shaft  makes  five  hundred  revo  utions  per  minute,  with  a  battery 
of  forty  cells,  producing  one-tenth  of  one-horse  power,  and  at 
an  expense  of  about  twenty-nine  cents  per  cell  for  forty-eight 
hours. 

423.  Tho  expanse  of  Electro-mag-netisin  compared  with 
Ctoam.  As  yet  electro-magnetic  engines  have  not  been  intro- 
duced to  any  extent,  because  the  expense  of  the  zinc  and  acids 
which  they  consume  is  far  greater  than  that  of  the  coal  required 
to  produce  an  equal  force  by  means  of  steam.  Careful  experi- 
ments have  shown  that  the  economic  difference  between  a  steam 
and  an  electro-magnetic  engine,  is  as  follows : 

A  grain  of  coal  burned  under  the  boiler  of  a  Cornish 

engine,  lifted 143  Ibs.  1  foot  high. 

A  grain  of  zinc  consumed  in  a  battery  to  move  an 

electro-magnetic  engine,  lifted    ......       80  Ibs.  1  foot  high. 

The  cost  of  coal  is,  per  cwt., 9c/. 

The  cost  of  zinc  is,  per  cwt., 216c?. 

There  is  considerable  diversity  of  opinion  as  to  the  amount 
of  zinc  consumed  in  the  production  of  one-horse  power.  Page 
computes  the  consumption  of  zinc  in  his  engine  at  3  Ibs.  of 
zinc  per  day,  for  one-horse  power.  Joule  calculates  the  con- 
consumption  under  the  most  favorable  circumstances,  at  45  Ibs. 
per  day,  for  one-horse  power  in  Grove's  battery,  and  in  Dan- 
iell's  battery  at  75  Ibs.  There  are  also  other  disadvantages :  the 
combustion  of  metals  witli  a  three  or  four-horse  power  engine,  is 
very  rapid  at  all  the  points  where  the  current  is  broken  in  de- 
magnetizing the  electro-magnets.  The  power  is  also  appplied 
at  a  great  mechanical  disadvantage,  and  the  conversion  of  elec- 

427  Describe  Stewart's  electro-motor. —428-  State  the  comparative  expense  of  eleetro- 
magnetism  and  steam. 


»  POWER    COMPARED    WITH    STEAM.  415 

tro-magnetism  into  mechanical  force  is  attended  with  mu2h  more 
loss  than  the  conversion  of  heat  into  motion  in  the  steam- 
engine.  This  is  due  in  part  to  the  very  great  reduction  in  the 
power  of  the  magnet  the  instant  the  armature  is  separated  from 
it ;  and  the  larger  the  magnets  and  engines,  the  greater  the  loss 
of  power.  These  objections  are  less  applicab'e  to  Pace's  en- 
gine, constructed  on  the  axial  principle,  than  any  other.  The 
cost  per  day,  however,  is  not  necessarily  conclusive  against 
these  engines ;  notwithstanding  the  great  expense  they  inny, 
under  certain  circumstances,  be  usefully  applied,  especially 
in  trades  and  occupations  of  small  capital,  where  the  abso- 
lute amount  of  mechanical  power  is  a  matter  of  less  conse- 
quence than  the  facility  of  producing  it  instantaneously  and  at 
will :  this  would  be  the  case  even  though  the  power  should  co  t 
twenty  times  as  much  as  the  sama  a  nount  furnished  by  a 
Cornish  steam  engine.  To  this  must  be  added  th '  important 
consideration  of  perfect  safety  and  the  entire  freedom  from 
the  danger  of  explosion, 

429.  Electro-magnetic  Clocks,  Electro-magnets  are  often 
used  as  a  motive  power  in  clocks.  The  oscillation  of  the  pendu- 
lum establishes  and  breaks  the  connection  between  an  electro- 
magnet and  a  battery,  in  such  a  way  as  to  give  to  the  pendulum 
by  the  raising  and  dropping  of  an  armature,  sufficient  impulse  to 
maintain  its  motion.  This  interrupted  connection  may  be  com- 
municated by  a  wire  to  all  the  clocks  in  a  large  city,  and  cause 
them  to  move  at  exactly  the  same  rate,  and  thus  one  central 
clock  may  become  the  motor  and  regulator  of  an  unlimited 
number  of  time-pieces.  Such  clocks,  however,  steadily  deterio- 
rate in  consequence  of  the  rapid  combustion  which  takes  plac^ 
at  the  points  where  contact  with  the  battery  is  made  and 
broken ;  and  for  this  reason  a  clock  of  ordinary  construction 
moved  by  a  weight  and  spring,  is  employed  to  furnish  the 
standard  time,  and  its  pendulum  as  it  oscillates  is  used  to  reg- 
ulate the  current  which  turns  the  hands  upon  an  indefinite 
number  of  electrical  dials.  Fig.  211  represents  a  dial  of  th;s 
description,  and  Fig.  212,  the  mechanism  by  which  its  hands 
are  turned.  An  electro-magnet,  B,  is  used  to  attract  an  arma- 
ture of  soft  iron,  p,  turning  on  a  pivot,  a.  This  armature  trans^ 
mits  its  motion  to  a  lever,  s,  which  by  means  of  a  ratchet  turns 
the  wheel  A.  This,  by  the  pinion  D,  turns  the  wheel  c,  and 

4?9  How  miy  a  pendulum  he  made  to  oscillate  by  electro -m;i:»netisni  ?  How  may 
on4  clock  bo  made  to  indicate  time  on  many  dials  in  different  places  7  Describe  Ftsi. 
2U  ami  213 


416  ELECTRO-MAGNETIC    CLOCKS. 

Fig.  211.  Fig.  212. 


Tlie  Electro-magnetic  Clock. 

this,  by  a  series  of  wheels  and  pinions,  moves  the  hands.  The 
regular  motion  of  the  hands  depends  upon  the  regularity  of  the 
oscillations  of  the  armature  P,  and  this  regularity  is  maintained 
by  making  and  breaking  the  connection  between  the  electro-mag- 
net B,  and  the  battery,  by  the  movement  of  the  pendulum  of  the 
standard  clock  mentioned  above.  In  this  manner,  all  the  clocks 
in  a  city,  in  a  large  hotel,  or  on  the  line  of  a  railroad,  may  be 
made  to  indicate  exactly  the  same  time,  for  the  electrical  cur- 
icnt,  travelling  at  the  rate  of  18,780  miles  in  a  second,  takes 
but  an  inappreciable  time  to  traverse  the  who!e  line.  Mr. 
Bain  has  invented  an  electrical  clock  which  is  driven  by  the 
current  derived  from  an  earth-battery,  consisting  of  one  zinc 
and  one  carbon  plate,  imbedded  in  the  ground,  about  four  feet 
apart  and  three  feet  deep.  §414,  p.  385. 

The  exact  time  when  the  sun  or  a  star  crosses  the  meridian 
at  one  observatory,  can  be  telegraphed  instantaneously  to  others, 
and  to  distant  places:  and  it  is  thus  that  the  exact  time  of  noon 
is  flashed  from  a  central  observatory  to  many  distant  points. 
Time  at  Hartford  is  telegraphed  from  New  York,  and  this  from 
the  Dudley  Observatory  at  Albany.  Other  applications  have 
been  made  of  electro-magnetism  to  the  bells  of  hotels  and 
hou.-es,  and  other  minor  conveniences  of  house-keeping. 

How  can  time  be  transmitted  from  one  place  to  another  ? 


THE    ELECTRIC 


417 


430.  The  Slcctric  Fire-Alarm.  One  of  the  most  interesting 
and  useful  applications  of  galvanic  electricity  is  to  the  construc- 
tion of  the  fire-alarm  of  cities.  A  central  office  is  established, 
where  a  battery  is  placed  which  is  always  in  aciion.  From  this 
a  wire  proceeds  to  every  part  of  the  town,  and  is  carried  at  suit- 
able points,  into  the  interior  of  iron  boxes  fixed  at  the  corners 
of  the  streets :  after  entering  each  box  the  wire  again  emerges, 
and  is  carried  to  the  next  box,  and  so  on  in  succession  through 
them  all,  and  is  finally  returned  to  the  opposite  pole  of  the 
battery  from  which  it  started.  Thus  an  electrical  current  is 
constantly  kept  in  circulation  through  every  part  of  the  entire 
city  circuit.  The  internal  arrangement  of  the  box  is  repre- 
sented in  Fig.  213.  The  current  enters  at  o,  by  means  of  an 


The  Electric  Fire-Alarm, 


430.    Describe  the  Electric  Fire-Alarm.     Describe  the  arrangement  of  the  wire.     How 
IB  tue  cur.i'ut  broken.' 


418  FIRE 

insulated  wire,  taking  the  course  indicated  by  the  arrow?,  de- 
scending in  the  space  between  the  outer  and  inner  boxes,  as  far 
as  n,  and  then  ascending  and  passing  into  the  interior  circular 
box  until  it  reaches  B  :  B  is  a  lever  of  wood,  having  its  upper 
surface  covered  by  a  thin  strip  of  metal,  which  by  means  of  a 
s;>r,ng  is  firm'y  pressed  aga'nst  the  brass  wheel  w.  By  the 
side  of  the  lever  B,  is  a  second  lever  which  is  con  ealed  in  the 
Fig.,  constructed  of  wood,  of  the  same  dimensions,  and  having 
its  upper  surface  covered  also  with  a  thin  metallic  strip,  which 
is  in  Ike  manner  pressed  firmly  upon  the  wheel  w,  by  means 
of  a  spring.  Although  these  levers  are  placed  side  by  side, 
there  is  no  direct  metallic  communication  between  them,  except 
by  means  of  the  wheel  w.  The  current,  when  it  reaches  the 
first  lever,  B,  descends  upon  the  brass  Ftrip  which  covers  its 
upper  surface,  to  w,  through  which  it  passes  to  the  second  lever, 
behind  B,  and  ascends  by  the  brass  strip  which  covers  it,  to  the 
upper  end,  whence  it  pusses  by  the  wire  as  indicated  by  the 
arrow,  to  the  electro-magnet  E.  After  circulating  through  both 
arms  of  the  electro-magnet,  it  emerges  and  parses  by  the  wire 
in  front  of  the  bell  G,  to  the  lower  part  of  "the  box,  and 
thernce  by  the  wire  p,  ascends  in  the  space  between  the  outer 
and  the  inner  box  to  the  po^nt  o,  where  it  again  enters  the  iron 
tube  through  win  -h  it  ha  1  descended,  and  pa-ses  on  to  the  nc  xt 
adjoining  box.  It  will  be  observed  that  so  long  as  both  levers, 
B,  rest  upon  the  wheel  w,  the  electric  current  circulates  uninter- 
ruptedly through  the  apparatus :  and  that  when  one  or  both 
the  levers  cease  to  press  upon  the  wheel  w,  the  current  craves 
to  circulate.  When  a  lire  occurs,  the  box  must  be  opened  and 
the  lever,  L,  pushed  down  as  for  it  can  be  made  to  go.  This 
movement  winds  up  a  spring  and  sets  in  motion  a  train  of  wheels 
by  which  motion  is  communicated  to  the  wheel  w.  This  wheel 
is  not  continuous,  but  is  broken  by  notches  in  its  circumfer- 
ence As  each  notch  comes  successively  beneath  the  levers 
B,  their  connection  with  the  wheel  w,  is  broken,  and  the  current 
c -ases  to  flow:  this  immediately  de-magnetizes  the  electro- 
magnet r,  and  allows  its  armature  A,  to  drop :  at  the  same 
instant  the  current  cea?es  to  circulate  through  the  entire  city 
CTCuif,  and  by  releasing  an  armature  attached  to  an  electro- 
magnet in  a  central  tower,  sets  in  motion  a  train  of  machinery 
by  wlii.  h  a  heavy  blow  is  struck  once  by  a  powerful  hammer 
upon  the  Fire  Bell,  and  an  alarm  sounded.  As  the  wheel  w, 

What  must  be  done  when  an  alarm  is  to  be  sounded  1 


ALARM.  419 

revolves,  and  each  notch  passes  on,  the  communication  between 
the  levers  B,  and  the  wheel  w,  is  re-established,  the  entire  city 
c'rcuit  is  again  rendered  complete,  the  armature  of  the  electro- 
magnet is  aga^n  drawn  up,  and  the  machinery  in  the  central 
tower  is  stopped,  one  blow  only  having  been  struck  upon  the  bell. 
If,  however,  there  be  more  than  one  notch  in  the  wheel  w, 
as  it  revolves  the  process  is  presently  repeated,  and  a  second 
blow  is  given  upon  the  bell.  These  notches  may  be  cut  quite 
near  each  other,  at  regular  intervals,  or  far  apart  and  at  unequal 
distances:  thus  many  combinations  may  be  effected,  by  which 
a  variety  of  blows  may  be  struck  upon  the  bell,  characteristic 
of  each  box,  and  determining  the  locality  of  the  fire.  Each 
box  is  distinguished  by  a  number,  and  the  notches  are  cut  i;i 
such  a  manner  as  to  strike  this  number  upon  the  bell.  Thu  -, 
if  two  notches  be  cut  quite  close  together,  and  then,  at  some  dis- 
tance from  them,  four  other  notches  at  equal  distances  from 
each  other,  the  effect  will  be  to  strike  two  strokes  in  rapid  suc- 
cession, and  then,  after  a  brief  interval,  four  others,  denoting  the 
number  24,  and  indicating  that  box  24  is  the  one  neare4  tti3 
fire.  By  pulling  the  lever  L,  down  once,  the  machinery  is 
wound  up  just  enough  to  make  the  wheel  \v,  revolve  five  times, 
and  thus  the  number  2  4,  in  the  above  case,  will  be  repeated  five 
time?.  With  every  completion  of  the  circuit,  the  armature  of  the 
electro-magnet  in  each  box  is  drawn  violently  back  to  the  mag- 
net, and  a  stroke  given  upo'i  the  bell  G.  The  alarm  is  there- 
fore repeated  in  every  iron  box  in  the  city,  and  may  be  made 
to  indicate  the  locality  of  the  fire  in  every  engine-hojse.  The 
box  is  kept  securely  locked,  and  the  lever  L,  is  moved  by 
means  of  a  projecting  pin,  L,  upon  the  inside  of  the  open  door, 
repre -enfed  in  the  Fig.  This  pin  extends  through  the  door,  and  • 
may  be  moved  upon  the  opposite  side  while  the  door  is  closed : 
s  s,  are  springs  for  the  purpose  of  restoring  the  pin  L,  to  its 
former  po  ition  after  being  once  thrust  down.  The  whole  box 
is  closed  by  an  external  do:>r  not  represented  in  the  Fig.,  the 
key  of  which  is  kept  in  ?ome  neighboring  house.  In  some 
case?,  the  alarm  is  first  telegraphed  to  a  central  office,  and  from 
that  transmitted  to  a  number  of  Fire-bells  distributed  over  the 
city.  The  advantage  of  making  use  of  a  circuit  which  is  con- 
stantly closed,  instead  of  bringing  the  battery  into  use  only  at 
the  moment  when  the  alarm  is  to  be  sounded,  is,  that  it  furnishes 
evidence  of  being  constantly  in  working  order,  and  makes  the 

How  is  the  number  of  tae  box  struck  upon  the  bell  f 


422"  IN    ELECTRO-MAGNETISM. 

with  the  same  amount  of  galvanic  force,  was  increased  several 
times,  and  it  was  found  that  a  current  transmitted  through  a 
long  wire  could  be  used  to  create  a  powerful  electro-magnet  at 
the  distance  of  many  miles,  and  make  signals  by  striking  a  bell, 
especially  if  a  battery  of  intensity,  §341,  con.-isting  of  ninny 
cells,  was  employed.  This  discovery  made  the  (on.-truction  of 
an  electro-magnetic  telegraph,  which  had  been  tried  without 
success  in  EngUmd  in  1825,  a  possibility,  and  served  as  the 
foundation  for  Morse's  electro-magnetic  instrument.  Prof.  Henry 
still  further  increased  the  power  of  the  electro-magnet  by  using 
a  number  of  separate  coils,  having  independent  connection  with 
the  battery,  on  the  same  horse-shoe,  in  place  of  one  long  single 
coil.  In  this  manner  the  powerful  electro-magnets  capable  of 
sustaining  from  five  to  ten  thousand  pounds  were  made,  which 
have  since  been  u  ed  in  the  construction  of  electro-motors. 
He  also  exhibited  the  first  mechanical  motion  ever  produced 
by  magnetic  attraction  and  repulsion,  by  means  of  a  vibrating 
beam  placed  horizontally  over  two  upright  magnets :  a  fly-wheel 
was  subsequently  attached  to  this,  and  afterwards  a  rotatory 
motion  given.  An  account  of  this  instrument  is  contained  in 
Silliman's  Journal  for  1831. 

Finally,  the  constant  battery  of  Prof.  Daniell  was  invented  in 
183G  ;  the  possibility  of  using  the  earth  as  a  part  of  the  tele- 
graphic circuit,  was  discovered  by  Stcinhcil  in  1837  ;  and  in  the 
same  year  these  principles  were  applied  by  our  countryman, 
Prof.  Morse,  to  the  construction  of  the  electro-magnetic  telegraph. 
About  the  same  time,  Wheatsfone  and  Cooke's  needle  telegraph 
was  introduced  in  England;  Daniell's  and  Grove's  batteries 
were  perfected  in  1843;  and  the  first  telegraph  line  in  the 
U.  S.  A.  erected  between  Baltimore  and  Washington  in  1844. 


THE  SECONDARY  CURRENT 


423 


,  §  IV.    Galvanic  Induced  Electricity. 

433.  Volta-STestric  Induction.  An  induced  secondary 
electrical  current  produced  by  establishing-  and  breaking-  the 
primary  current  of  a  Galvanic  Dattsry.  We  have  seen  tlmt 
the  frictional  electricity  of  the  machine  induces  electricity  in  all 
surrounding  bodies,  §310.  The  electricity  of  the  battery  acts  in  a 
similar  manner,  but  only  at  the  instant  when  the  current  begins, 
and  at  the  instant  when  it  ceases,  to  flow :  during  its  continu- 
ous flow,  no  inductive  influence  whatever  is  exerted  by  it.  This 
fact  was  discovered  by  Mr.  Faraday,  in  1831.  He  found  that 
a  wire  transmitting  a  powerful  current,  induces  a  momentary 
current  in  a  second  wire  parallel  to  the  first,  the  two  extremi- 
ties of  which  are  brought  together,  and  united  so  a;  to  form  a 
closed  circuit,  whenever  the  connection  of  the  original  wire  with 
the  battery  is  made,  or  is  broken.  This  he  called  Volta-  Electric 
Induction.  The  effect  is  much  increased,  if  instead  of  employ- 
in;;  simple  parallel  wires,  the  wires  of  the  two  currents  are 
coiled  into  two  helices  and  arranged  one  within  the  other.  The 
wire  which  conveys  the  primary  current,  or  the  primary  coil, 
is  placed  in  the  axis  of  the  coil  for  the  secondary  current,  and 
the  extremities  of  the  secondary  coil  are  joined  together  so 
a<  to  form  a  closed  or  continuous  circuit.  A  galvanometer  is 
connected  with  the  extremities  of  the  secondary  co'l,  in  such  a 
manner  as  to  form  a  part  of  the  closed  circuit,  for  the  purpose 
of  demonstrating  the  actual  passage  of  the  current.  The  pro- 
duction of  a  secondary  current  under  these  circumstances,  may 
be  shown  by  the  apparatus  repre'sented  in  Fig.  214.  Let  r 


Volta  Electric  Induction. 


-. ... „.  ....  „„ ..Jlv  on  al!  other'  nor  it  ?     Whnt  is  the  eff.-c  t  of  a 

wire  e.-irr.injr  a  current  upon  n  c'o  e  1  i  a  allel  wire?'    TT"  "  — •"  M"J  <•""/-«•  ».«.  i,,n,ooea^» 


Wluit  is  the  effect  of  fin  electrified  ho 
'    e  1  i  a 


ire  e.-irr.injr  . a  current  upon  n  f'o  e  1  i  a  ;iHel  wire?     Ho.v  c.-m  this  effect  »>e  increased? 
»'  '  >  discover..;  1  t',ie;«.-fa,ct.-i?     Wait  11.1111  •  d.d  iie.ji.'e  to  t.iis  i.idactive  action? 

ib 


424  INDUCED  BY  THE  BATTERY.  > 

represent  the  inner  primary  helix,  composed  of  a  short  piece 
of  stout  wire  carefully  wound  with  silk  or  cotton  and  varn'shed 
with  gum-lac,  so  as  to  be  thoroughly  insulated,  and  having 
its  two  extremities  connected  with  the  binding  cups  d  and  c, 
through  which  a  connection  is  established  with  the  battery. 
Let  s,  represent  the  outer  secondary  helix,  composed  of  a  great 
length  of  very  fine  copper  wire,  also  carefully  insulated,  and 
entirely  separated  from  the  primary  helix,  and  having  its  ex- 
tremities connected  with  the  binding  cups  a  and  b,  through 
which  a  connection  is  established  with  the  galvanometer  o,  thus 
forming  a  closed  circuit,  of  which  the  galvanometer  is  a  part. 
The  connection  of  the  primary  helix  with  the  battery  is  made 
or  broken  at  pleasure  by  connecting  or  disconnecting  the  bat- 
tery wire,  by  means  of  the  hand,  with  the  binding  cup  c.  It  is 
found  that  the  moment  the  connection  is  completed  with  the 
battery,  and  the  galvanic  current  begins  to  circulate  through 
the  inner  primary  coil  P,  a  secondary  current  of  positive  elec- 
tricity instantly  circulates  in  an  opposite  direction  throrgh  the 
outer  coil,  shown  by  the  violent  oscillations  of  the  needle  of  the 
galvanometer.  This  pecondary  current  continues  only  for  a 
moment  and  almost  immediately  cea  es.  If  the  connection  of 
the  primary  coil  with  the  battery  be  kept  up,  the  flow  of  the 
induced  secondary  current  ceases,  as  is  shown  by  the  needle  of 
the  galvanometer  returning  to  its  position  of  rest.  Again,  the 
instant  that  the  connection  of  the  primary  col  r,  with  the  bat- 
tery is  broken  by  removing  the  battery  wire  from  the  binding 
cup  c,  arid  the  primary  current  cea?es  to  flow  through  P,  a  mo- 
mentary secondary  current  of  positive  electricity,  flowing  in  the 
same  direction  with  the  primary  current,  circulates  throughout 
the  entire  coil,  shown  by  the  powerful  impulse  which  it  imparts 
to  the  needle  of  the  galvanometer.  These  currents  are  only 
momentary,  but  are  characterized  by  great  power  and  intensity. 
Though  the  current  of  positive  electricity  is  only  spoken  of,  ac- 
cord'  ny  to  the  principle  laid  down,  §033,  p.  309,  it  must  be  under- 
stood, that  a  momentary  current  of  secondary  negative  electricity 
is  also  produced  at  the  same  time,  flowing  in  the  opposite  direc- 
tion to  that  of  the  secondary  positive:  when  contact  wi;h  the 
battery  is  completed,  it  circulates  in  the  Fame  direction  with  the 
primary  current :  when  contact  with  the  battery  is  broken,  it 
circulates  in  the  opposite  direction.  The  secondary  electric 
current  thus  induced  is  not  derived  from  the  battery,  nor  from 

I)f><<orihe  the  apparatus  by  which  these  ejects  may  be  demonstrated.     la  a  Bejativ* 

as  v.  Ji  a  •;  a  positive 


HISTORY   OP  425 

the  primary  current ;  it  is  the  electricity  natural  to  the  secon- 
dary wire,  the  equilibrium  of  which  has  been  disturbed  by  the 
sudden  production  and  cessation  of  the  primary  current  in  its 
vicinity :  if  the  secondary  wire  be  very  short,  the  amount  of 
induced  electricity  is  very  small,  because  the  amount  of  matter 
exposed  to  the  action  of  the  primary  current  is  very  Lttle,  and 
the  amount  -of  electricity  which  it  contains  very  trifling :  if 
the  wire  be  increased  in  length  the  induced  rlectric-ity  man- 
ifested is  correspondingly  increa-ed,  because  of  the  larger 
amount  of  matter  operated  upon,  and  the  larger  amount  of  elec- 
tricity whose  equilibrium  is  disturbed  by  the  operation  of  the 
primary  current.  It  is  essential  to  the  complete  success  of 
these  experiments,  that  the  secondary  wire  should  be  much 
longer  and  finer  than  the  primary. 

434.  Faraday's  Experiments.  In  Mr.  Faraday's  origi- 
nal experiments  the  helices  were  arranged  as  follows :  "  About 
twenty -six  feet  of  copper  wire,  one-twentieth  of  an  inch  in  di- 
ameter, were  wound  round  a  cylinder  of  wood  as  a  helix,  the 
different  spires  of  which  were  prevented  from  touch'ng  by  »a 
thin  interposed  twine :  this  helix  was  covered  with  calico,  and 
then  a  second  wire  applied  in  the  same  manner.  In  this  way 
twelve  helices  were  super-imposed,  each  containing  an  average 
length  of  twenty-seven  feet,  and  all  in  the  same  direction.  The 
first,  third,  fifth,  seventh,  ninth,  and  eleventh,  of  these  helices, 
were  connected  at  their  extremities,  end  to  end,  so  as  to  form 
one  helix :  the  others  were  connected  in  a  similar  manner ;  and 
thus  two  principal  helices  were  produced  closely  interposed, 
having  the  same  direction,  not  touching  anywhere,  and  each 
containing  one  hundred  and  fifty-five  feet  in  length  of  wire. 
One  of  these  helices  was  connec-ted  with  a  galvanometer,  the 
other  with  a  voltaicjj)attery  of  ten  pairs  of  plates  four  inches 
square,  with  double  coppers,  and  well  charged;  yet  not  the 
slightest  sensible  deflection  of  the  galvanometer  needle  could  be 
observed.  Then  two  hundred  and  three  feet  of  copper  wire 
in  one  length  were  coiled  around  a  large  blodt  of  wood :  other 
two  hundred  and  three  feet  of  similar  wire  were  interposed  as  a 
spiral  between  the  turns  of  the  first  coil,  and  metallic  contact 
everywhere  prevented  by  twine.  One  of  these  helices  was 
connected  with  a  galvanometer,  and  the  other  with  a  battery  of 
one  hundred  pairs  of  plates  four  inches  square,  with  double 

la  the  secondary  current  derived  from  the  battery  or  the  primary  current?  What  ia 
5t  t  source  ?  W>iat  Is  the  effect  of  lengtheuing  the  secondary  coil  ? — 434.  Give  the  history 
of  Mr.  i'araday's  discovery. 


426  THE   DISCOVERY. 

coppers,  and  well  charged.     When  the  contact  was  made,  there 
was  a  sudden  and  very  slight  effect  at  the  galvanometer,  and 
there  was  also  a  slight  similar  effect  when  the  contact  with  the 
Lattery  was  broken.     But  whilst  the  voltaic  current  was  cont:n- 
tiing  to  pass  through  the  one  helix,  no  gulvanometrical  appear- 
ances nur  any  effect  like  induction  upon  the  other  helix  could 
La  perceived,  although  the  active  power  of    the  battery  was 
p/oved  to  be  great  by  its  heating  its  own  helix,  and  by  the  bril- 
liancy of  the  discharge  when  made  through  charcoal.     Repeti- 
tion of  the   experiments  with  a  battery  of  one  hundred   and 
twen  y  pairs  of  plates,  produced  no  other  effects :  lut  it  was 
ascena  ried,  loth  at  this  and  the  former  time,  that  the  slight 
deflection  of  the  needle  occurring  at  the  momeitt  of  ccmpletii  g 
the  connection,  was  always  in  one  direction,  and  that  the  equal  y 
slig'it  deflection  produced  when  the  contact  was  broken,  was  in 
the  other  direction ;  and  also  that  there  effects  occurred  when 
the  first  helices  were  used.     The  results  which  I  had  by  this 
time  obtained  with  magnets  led  me  to  believe  that  the  lattery 
current  through  one  wire  did  in  reality  induce  a  similar  current 
through  the  other  wire,  but  that  it  continued  for  an  instant  cnly, 
and  partook  more  of  the  nature  of  an  electrical  wave  parsed 
thro  igh  from  the  shock  of  a  common  Leyden  jar,  than  of  the 
current  from  a  voliaic  battery,  and  therefore  might  magnetize 
a  ste*jl  needle,   though   it   scarcely  affected  the  galvanometer. 
This  expectation  was  confirmed;    for  on  substituting  a  small 
hollow  helix,  formed  round  a  glass  tube, for  the  galvanometer, 
introducing  a  steel   needle,   making   contact  as  before  between 
the   battery   and   the   inducing   wiie,   and  then  ronr.oving   the 
needle  be'ore  the  battery   ( on' act  was    broken,  it  was    fbur.d 
magnetized."     In  these  experiments  of  Mr.  Faraday,  it  will  be 
observed  that  the  secondary  wire  wras  no  longer  than  the  pri- 
mary wire,  and   consequently  the   results    obtained  were  ex- 
tremely feeble;  the  cur.^nt  obtained  from  the  secondary  wire 
had  in  fact  less  intensity  than  that  obtained  from  the  pr,mary%: 
no  effect  was  produced  upon  the  tongue,  no  sparks,  no  heat  ng 
of  fine  wire  or  charcoal,  no  chemical  effects ;  the  current  was 
indicated  on'y  by  the  galvanometer  and  by  its  magnetic  effects : 
no  additional  effect  was  produced  by  increasing  the  size  of  the 
battery  from  1 0  cells  to  1 20.     If  the  coils  had  been  unequal,  the 
shorter  used  for  the  primary,  and  the  longer  for  the  secondary, 
>ery  different  results  might  have  been  obtained.     This  reversal 

What  effect  would  have  been  produced  had  Mr.  Faraday  used  a  longer  secondary  coil? 
Who  first  iutioduced  the  use  of  tue  kmg  secondary  coii  ? 


INDUCTION    TAKES    PLACE 


427 


of  the  relative  length  of  the  coils  was  first  made  by  our  coun- 
tryman,  Dr.  Page  :  by  making  u-e  of  a  short  primary  coll,  and 
a  secondary  coil  320  feet  in  length  he  established  the  prin- 
ciple, that  to  obtain.  induced  currents  of  high  intensity  f.om 
a  battery  of  a  single  or  only  a  few  pairs  of  plates,  the  induced 
or  secondary  circuit  must  be  much  longer  th:m  the  induc'n* 
or  battery  circuit.  By  employing  a  short  primary  coil,  and  a 
secondary  coil  of  copper  ribbon  220  feet  in  length  and  one  inch 
wide,  powerful  shocks  were  obtained,  a  Leyden  jar  charged,  and 
water  decomposed,  by  the  action  of  the  secondary  current  :  with 
a  coll  320  feet  in  length,  a  secondary  current  was  obtained  of 
sufficient  intensity  to  pass  between  charcoal  points  before  con- 
tact. The  establishment  of  this  principle  led  to  the  construction 
of  several  important  instruments  for  the  development  of  secon- 
dary electricity,  and  eventually  to  that  of  Ruhmkorff's  coil. 

£35.  The  inductive  elFect  of  the  Primary  current  ta^ea 
place  through  a  considerable  distance.  The  inductive  influ- 
ence of  the  primary  current  takes  place  even  when  the  primary 
and  secondary  coils,  are  not  placed  one  within  the  other,  but  are 
separated  by  a  considerable  distance.  Thus  in  Fig.  215,  let  L, 


.  215. 


9         L 


The  Secondary  Induced  Current. 


represent  one  cell  of  a  Daniell's  battery ;  A,  the  primary  coil, 
composed  of  a  short  strip  of  copper  ribbon,  and  having  one  of 
its  extremities  permanently  connected  with  the  positive  pole 
of  the  battery,  while  the  other  is  arranged  in  such  a  way  that 
its  connection  with  the  negative  pole  may  be  made  and 
broken  at  pleasure  by  drawing  the  negative  wire  over  the 
ribbed  piece  of  iron  which  terminates  it :  w,  is  the  secondary 
coil,  consisting  of  a  great  length  of  fine  copper  wire,  separated 

435.  Will  induction  take  place  even  if  the  coils  are  separated  from  each  other  ?    How 
can  tnis  be  proved  ? 


428  THROU&H    A    CONSIDERABLE    DISTANCE.  ^ 

to  a  considerable  distance  from  the  primary  coil  A,  and  having 
its  two  extremities  connected  with  the  handles.  As  the  wire, 
connecting  the  primary  coil  with  z,  passes  from  one  ridge  of 
the  piece  of  ribbed  iron  to  another,  the  primary  circuit  is  rap- 
idly completed  and  broken,  and  a  succession  of  powerful  induced 
momentary  currents  alternately  in  opposite  directions,  circulates 
through  the  secondary  coil  w,  by  which  a  torrent  of  sharp 
shocks  are  given  to  the  moistened  hands.  It  will  be  observed 
that  the  extremities  of  the  coil  \v,  being  connected  with  the 
handles,  the  body  of  the  experimenter  together  with  the  secon- 
dary coil,  constitutes  a  closed  circu:t.  This  inductive  action  is 
*  obtained  even  though  a  plate  of  glass  be  interposed  between 
A  and  w,  but  if  a  plate  of  metal  be  interposed  no  inductive  ac- 
tion takes  place  in  the  coil  w,  because  it  is  transferred  to  the 
interposed  conducting  metallic  plate.  When  the  coil  w 
contains  several  thousand  feet  of  fine  wire,  the  shocks  are  too 
intense  to  be  endured.  The  intensity  of  the  shocks,  however, 
diminishes  in  a  rapid  ratio,  as  the  distance  between  the  coils  is 
increased.  With  the  arrangement  represented  in  Fig.  215, 
shocks  through  the  tongue  are  easily  obtained  when  the  wire 
coil  is  a  foot  or  two  above  the  ribbon  toil,  and  the  distance  may 
be  still  further  increased  by  using  a  larger  ribbon  co'l  or  a  mo;  e 
powerful  battery.  The  shocks  are  made  much  more  violent 
by  wetting  the  hands  with  salt  water.  The  intensity  of  the 
shock  aLo  diminishes  rapidly  as  the  secondary  coil  w  is  raised 
from  a  horizontal  position  into  an  inclined  one,  and  when  it  is 
elevated  into  a  vertical  position,  its  edge  resting  on  the  primary 
co'l,  they  are  no  longer  felt.  These  induced  currents  not  only 
give  powerful  shocks,  but  also  magnetize  steel  needles,  and  pro- 
duce chemical  decomposition :  the  former  may  be  shown  by 
placing  a  sewing-needle  in  the  centre  of  the  coil  w,  when  it 
w  11  instantly  be  made  permanently  magnetic ;  and  the  latter 
by  disconnecting  the  extremities  of  the  coil  w  from  the  handles, 
and  connecting  them  with  platinum  wires  dipped  into  acidulated 
water,  or  into  a  solution  of  iodide  of  potassium.  The  charac- 
ter of  the  induced  secondary  current  depends  very  much  upon 
the  arrangement  of  the  secondary  coil  w:  if  it  be  <ompocedof 
a  long  ribbon  of  copper,  offering  a  large  sectional  area  for  the 
conduction  of  the  current  and  diminishing  resistance,  at  the 
same  time  that  the  different  layers  of  the  coil  are  approximated 
to  each  other  with  the  smallest  po-sible  interval  between  them, 

What  is  the  effect  of  an  interposed  gloss  plate?  What  effect  has  increase  of  distance 
upon  the  intensity  of  the  shocks  ?  of  placiug  the  coils  at  right  angles  ?  What  are  the 
effects  of  the  induced  currents  ? 


INDUCTION    TAKES    PLACE    ON    THE  429 

currents  of  large  quantity  are  obtained  like  those  required  for 
magnetizing  steel,  or  for  igniting  platinum  wire,  §34 1  :  but  if  it 
be  composed  of  a  very  thin  wire  a  secondary  current  is  obtained 
of  great  intensity,  producing  powerful  shocks,  and  intense? 
chemical  effects.  During  the  uninterrupted  circulation  of  (he 
primary  current  no  effect  is  perceived,  but  only  at  the  moment 
of  opening  or  closing  the  circuit.  The  secondary  current  which 
is  obtained  on  closing  the  primary  circuit,  is  called  the  initial 
secondary ;  and  that  which  is  obtained  on  breaking  the  primary 
circuit,  is  called  the  terminal  secondary.  When  a  battery  of  a 
single  pair  of  plates  is  employed,  the  initial  secondary  is  much 
inferior  in  intensity  to  the  terminal,  and  gives  a  feebler  shock  : 
the  intensity  of  the  terminal  secondary  preluded  by  breaking 
the  circuit,  is  very  little  increased  by  adding  to  the  number  cf 
the  battery  cells :  with  the  initial  secondary,  on  the  contrary,  ev- 
ery additional  pair  is  found  to  increase  its  intensity,  so  that  with 
ten  cells  it  is  found  to  equal  the  terminal,  and  with  a  larger  num- 
ber to  exceed  it :  in  quantity,  however,  the  secondary  currents 
both  initial  and  terminal,  are  equal,  those  produced  by  a  ribbon 
coil  being  much  superior  to  those  obtained  from  a  wire  coil. 

436.  Induction  of  a  momentary  Secondary  current  by 
ths  approach  and  removal  of  the  Primary  current.  Similar 
effects  may  be  produced  by  removing  the  primary  helix  r, 
in  Fig.  214,  from  the  secondary  helix  s,  and  causing  the  p:-i- 
mary  coil  p,  while  it  is  still  transmitting  tli3  battery  curren  , 
suddenly  to  approach  and  recede  from  the  secondary  coil,  as 
shown  in  Fig.  216.  During  the  approach,  a  secondary  current 
in  an  opposite  direction  is  set  on  foot  in  the  outer  coil,  as  sho\vn 
by  the  movement  of  the  galvanometer:  and  again  during  the 
withdrawal  a  momentary  secondary  current,  in  the  same  direc- 
tion with  the  primary  current,  is  made  to  circulate.  If  the  gal- 
vanometer be  removed  from  the  secondary  circuit,  and  in  its 
p'ace  a  small  wire  helix  substituted  so  as  to  make  a  continuous 
circuit,  and  a  soft  iron  wire  be  introduced  into  the  helix,  it  will 
be  made  temporarily  magnetic:  if  a  steel  needle  be  introduced 
it  will  be  permanently  magnetized,  and  the  intensity  of  the 
magnetism  will  be  proportioned  to  the  intensity  of  the  current. 
These  facts  were  also  discovered  by  Mr.  Faraday  in  1831,  at 
the  same  time  with  those  described  above,  and  his  experiments 
were  made  in  the  following  manner :  "  In  the  preceding  experi- 
ments the  wires  wete  placed  near  to  each  other,  and  the  contact 

What  is  the  effect  of  constructing  the  secondary  coil  of  copper  ribbon  ?  of  fine  copper 
wire?  What  is  the  initial  secondary  current ?  the  terminal  secondary?  How  do  they 
compare  in  intensity  and  quantity  ?— 436.  Show  how  induction  may  be  produced  by 
the  approach  and  removal  of  the  primary  coil  ?  Who  discovered  thi«  fact  ? 


430       APPROACH  AND  REMOVAL  OF  THE  PRIMARY  CURRKXT. 

Fie.  .216. 


The  Secondary  current  induced  by  the  approach  and  removal  of  the  Primary  coil. 

of  the  inducing  one  with  the  battery  made  when  the  inductive 
effect  was  required,  but  as  the  particular  action  might  be  sup- 
posed to  be  exerted  only  at  the  moments  of  making  and  break- 
ing contact,  the  induction  was  produced  in  another  way. 
Several  feet  of  copper  wire  were  stretched  in  wide  zig-zag 
forms  representing  the  letter  w,  on  one  surface  of  a  broad 
board :  a  second  wire  was  stretched  in  precisely  similar  forms 
on  a  second  board  so  that  when  brought  near  the  first,  the  wires 
should  everywhere  touch,  except  that  a  sheet  of  thick  paper  was 
interposed.  One  of  these  wires  was  connected  with  a  galvan- 
ometer, and  the  other  with  a  voltaic  battery.  The  first  wire 
was  then  moved  towards  the  second,  and  as  it  appronched,  the 
needle  was  deflected.  Being  then  removed,  the  needle  was 
deflected  in  the  opposite  direction.  By  first  making  the  wires 
approach  and  then  recede  simultaneously  with  the  vibrations 
of  the  needle,  the  latter  soon  became  very  extensive ;  but 
when  the  wires  ceased  to  move  from  or  towards  each  other, 
the  galvanometer  needle  soon  came  to  its  usual  position.  As 
the  wires  approximated,  the  induced  current  was  in  the  contrary 

How  were  his  experiments  conducted  ? 


THE    CONDITIONS    OF    INDUCTION.  4^1 

direction  to  the  inducing  current :  as  the  wires  receded,  the  in- 
duced current  was  in  the  same  direction  as  the  inducing  current. 
"When  the  wires  remained  stationary,  there  was  no  induced 
current.  All  these  results  have  been  obtained  with  a  voltaic 
apparatus  consisting  of  a  single  pair  of  plates." 

437.  Tii2  conditions  of  Induction,  and  properties  of  in- 
duced currents.     From  the   experiments  which  have  been  de- 
scribed, the  {blowing   principles  may  be  deduced:    1st.    The 
distance  remaining  the  tame,  a  continuous  and  constant  current 
does  not  induce  any  current  in  an  adjacent  conductor.     2d.  A 
current  at  the  moment  of  circulation   produces  an  inverse  in- 
duced current  in  an  adjacent  conductor.     3d.  A  current  the 
moment  it  ceases  produces  a  direct  induced  current.     4th.  A 
current  which  approaches  a  close!  circuit,  or  whose  intensity 
increases,  gives  rise   to  an  inverse  induced  current.      5th.  A 
current  which  is  removed,  or  whose  intensity  diminishes,  gives 
rise  to  a  direct  induced  current. 

The  electricity  of  the  in  luced  current  in  the  secondary  coil 
is  possessed  of  greater  intensity,  and  will  give  more  vivid  and 
louder  sparks  and  w  11  produce  more  violent  shocks  than  the 
primary  current,  especially  at  the  moment  when  the  connection 
of  the  primary  coil  with  the  batterv  is  broken  :  it  al  o  de  om- 
po.ses  water,  metallic  salts  and  the  like,  and  acts  upon  the  rnag- 
ne:ic  needle.  Induced  currents  are  more  powerful  the  longer 
the  wires  of  the  secondary  coil.  On  the  contrary,  the  primary 
coil  should  be  made  of  large  copper  wire  or  ribbon,  and  of  mod- 
erate length.  The  wires  of  both  co'ls  should  be  carefully 
vvound  with  silk  or  cotton,  and  covered  with  a  solution  of  shell- 
lie,  so  as  to  secure  perfect  insulation.  If  the  connection  of  the 
primary  coil  with  the  battery  be  completed  or  broken  very 
rapidly,  the  effect  of  a  continuous  current  of  secondary  elec- 
tricity is  secured.  The  direct  secondary  current,  produced  by 
breaking  connection  with  the  battery  and  the  primary  coil,  is 
ordinar,  ly  found  to  be  much  more  powerful  than  the  inverse 
secondary  current  produced  by  completing  connection,  §435. 

438.  Induction  of  a  current  on  itself.    The  extra  current  on 
breaking  and  completing-  the  primary  circuit.      If   the    wire 
connecting  the  two  poles  of  a  battery  be  short,  and  the  circuit 
suddenly  broken,  on'y  a  scarcely  perceptible  spark  is  perceived. 
If  the  ob  erver  fo:%m  part  of  the  circuit  by  holding  a  pole  of  the 
battery  in  each  hand,  no  shock  is  obtained  unless   the  current 

437.  State  the  conditions  of  induction,  and  the  properties  of  induced  currents.— 438. 
Does  induction  take  place  without  the  use  of  a  secondary  coil? 


432 


THE    EXTRA    CURRENT. 


be  very  intense.  If,  however,  the  connecting  wire  be  long  and 
fine,  and  especially  if  it  be  made  into  a  spiral  with  a  great  many 
turns  so  as  to  form  a  helix  with  very  close  folds,  a  very  vivid 
spark  is  produced  when  the  connection  is  broken,  although  o^y 
a  feeble  one  passes  when  the  connection  is  completed ;  and  an 
observer  in  the  circuit  receives  a  shock,  which  is  greater  the 
more  numerous  the  turns  of  the  coll.  This  effect  is  explained 
by  the  inductive  action  which  the  current  exerts  upon  the  wire 
which  it  traverses,  in  virtue  of  which  a  direct  induced  current, 
or  one  in  the  same  direction  as  the  battery  current,  is  induced 
in  the  wire  connecting  the  poles  of  the  battery,  whenever  the 
battery  circuit  is  broken.  To  show  the  existence  of  this  current 
at  the  moment  of  breaking  contact,  a  battery  may  be  arranged 
as  in  Fig.  217.  Two  wires  form  the  poles  of  the  battery,  E  and 


Fig.  217. 


The  Extra  Current.     The  Induction  of  a  current  on  itself. 

E',  and  are  connected  with  the  two  binding  cups,  r  and  D,  at  the 
extremities  of  a  coil  of  long  h'ne  insulated  copper  wire.  At  the 
points  A  and  c,  on  the  wires,  two  other  wires  are  connected 
with  the  galvanometer  G,  so  that  the  current  from  the  pole  E, 
branches  at  A,  into  two  currents,  one  circulating  through  the 
coil  B,  and  the  other  through  the  galvanometer  G,  and  both 
returning  to  the  negative  pole  E'.  As  soon  as  the  current  cir- 
culates, the  galvanometer  needle  is  deflected  from  G  to  a,  show- 
ing the  tendency  of  the  needle  to  move  in  that  direction: 

State  the  difference  of  effect  in  using  a  short  and  a  long  wire  to  connect  the  poles  of  a 
battery.  Explain  it.  How  can  the  existence  of  this  induced  current  be  proved? 
What  ia  meant  by  the  extra  current  ?  What  effect  has  it  upon  the  vividness  of  the  spark 
on  breaking  the  circuit?  on  completing  it? 


INDUCTION    OF    A    CURRENT    ON    ITSELF.  433 

.it  i.s  (hen  brought  back  to  zero,  and  kept  there  by  the  insertion 
of  a  pin  which  prevents  it  from  turning  in  the  direction  G  a, 
but  leaves  it  free  to  turn  in  the  opposite  direction.  Then  on 
breaking  contact  at  E,  the  needle  is  immediately  deflected  in 
the  direction  G  a,  showing  the  production  of  a  current  running 
contrary  to  that  of  the  battery  current ;  that  is,  from  c  to  A. 
But  the  battery  current  having  been  cut  off,  this  current  c  A 
must  traverse  the  closed  circuit  A,  F,  B,  D,  G  ;  that  is,  move  in 
the  same  direction  as  the  battery  current.  The  current  which 
thus  appears  when  the  battery  circuit  is  broken,  is  called  the 
extra  current,  or  the  direct  extra  current.  This  current  moving 
in  the  same  direction  as  the  battery  current,  greatly  heightens 
its  intensity,  and  accounts  for  the  vividness  of  the  spark  which 
is  produced  at  the  breaking  of  the  battery  circuit.  A  similar 
induced  current  is  also  produced  on  completing  the  battery  cii- 
cuit,  but  as  this  is  an  inverse  current  and  moves  in  the  contrary 
direction,  it  diminishes  the  intensity  of  the  battery  current,  and 
therefore  lessens  the  spark  which  appears  on  completing  the 
circuit,  and  accounts  for  its  feebleness. 

439.  Induction  of  a  Secondary  current  in  the  Primary 
wire  itself.  From  what  has  just  been  said,  it  appears  that 
whenever  the  connection  of  the  wires  joining  the  poles  of  the 
battery  is  made  or  broken,  a  secondary  current  is  induced  in 
the  primary  wire  itself.  This  induced  electrical  current  is  not 
derived  from  the  battery  current,  but  is  simply  a  portion  of 
the  natural  electricity  of  the  wire,  which  has  been  disturbed, 
decomposed  and  thrown  into  an  active  state  by  the  passage  of 
the  battery  current :  this  inductive  action  is  not  confined  simply 
to  the  wire  which  connects  the  poles,  but  also  extends  through 
the  battery  itself,  because  the  natural  electricity  of  the  plates 
of  which  the  battery  consists  has  also  been  disturbed  by  the 
passage  of  the  galvanic  current  through  them,  and  the  electrical 
current  thus  induced  is  added  to  that  which  has  been  excited  in 
the  wire  joining  the  poles.  This  induced  current  being  nothing 
but  the  disturbed  natural  electricity  of  the  wire  and  battery,  its 
strength  arid  quantity  must  depend  therefore  upon  the  amount  of 
matter  which  has  been  subjected  to  the  influence  of  the  battery 
current ;  i.  e.,  upon  the  length  of  the  wire  and  the  number  of 
plates  in  the  battery  :  it  is  also  affected  by  the  manner  in  which 
the  wire  is  arranged,  whether  wound  into  a  coil  or  carried  direct 
between  the  poles ;  also  by  the  force  of  the  primary  current ; 

439  Is  there  a  secondary  current  induced  in  the  primary  wire  itself?  What  is  the 
origin  of  this  current?  Is  it  confined  to  the  primary  wire  ?  Ou  what  does  its  strength 
and  quantity  depend  ?  ^_ 


434  INDUCTION    OF   A    SECONDARY    CURRENT 

and  by  the  suddenness  with  which  it  is  broken.  Thus,  when 
the  poles  of  a  small  galvanic  battery  consisting  of  a  single  pair 
of  plates,  are  connected  by  a  copper  wire  of  a  few  inches  in 
length,  no  spark  is  perceived  when  the  connection  is  either 
formed  or  broken,  or  at  the  most  only  a  very  faint  spark  at  the 
moment  of  breaking  the  circuit ;  but  if  the  wire  be  thirty  or 
forty  feet  in  length,  a  bright  spark  appears  at  the  moment  when 
the  connection  is  broken,  though  none  is  seen  at  the  moment 
when  the  connection  is  made.  By  coiling  the  wire  into  a  helix 
the  vividness  of  the  spark  is  increased ;  and  a  still  greater  ef- 
fect is  obtained  if  a  piece  of  soft  wire  is  introduced  info  the 
helix  and  converted  into  an  electro-magnet.  This  increase  of 
effect  when  a  coil  is  used  in  place  of  a  straight  wire,  seems  to 
be  due  to  the  inductive  action  of  the  adjoining  strands  upon 
each  other,  as  though  they  were  so  many  independent  wires ; 
for  it  must  be  remembered  that  the  secondary  current  is  not 
a  part  of  the  battery  current  which  is  rushing  through  the 
wire  as  through  a  conductor,  but  is  the  natural  electricity  of 
the  wire  itself  in  a  state  of  disturbance ;  and  the  greater  the 
disturbance  the  greater  the  strength  of  the  induced  current: 
the  breaking  of  the  battery  current  produces  a  disturbance 
of  the  natural  electricity  of  the  wire,  which  is  propagated 
through  its  whole  extent ;  and  then  if  this  wire  be  coiled  into  a 
helix,  the  induced  current  in  each  strand  is  increased  by  the 
inductive  influence  of  the  strands  on  each  side  of  it,  in  the  same 
way  as  it  would  be  if  these  strands  were  separate  pieces  of 
wire  in  a  highly  excited  electrical  state  suddenly  brought  near  it. 
The  increased  effect  imparted  to  the  current  by  the  introduc- 
tion of  the  soft  iron,  is  due  to  the  sudd<  n  disappearance  of  the 
magnetism  of  the  iron  as  soon  as  the  connection  is  broken,  the 
sudden  de-magnetization  of  an  electro-magnet  by  interrupting 
tli-'>  primary  current  which  actuates  it  being  always  accompanied 
by  the  production  of  a  secondary  current  in  the  same  direction 
with  the  primary,  as  will  be  more  fully  explained  presently,  §448. 
So  great  is  this  increased  effect,  that  though  a  battery  may  be 
so  weak  as  to  be  altogether  unable  to  produce  any  shock  or 
emit  the  ftiintcst  spark  when  its  extremities  are  connected  by  a 
short  wire,  the  instant  the  conducting  wire  is  lengthened  and 
coiled  into  a  helix,  within  which  a  rod  of  soft  iron  is  placed,  in 
consequence  of  the  powerful  induction  which  takes  place,  the 

Give  an  illustration.  Explain  the  increased  effect  produced  by  coiling  the  connecting 
wire  into  a  helix.  Explain  the  increased  effect  on  inserting  a  rod  of  soft  iron  iuto  the 
helix.  Give  experiments  in  illustration.  Is  there  any  difference  iu  effect  on  making  aud 
breaking  connection? 


IN    TIIS    PRIMARY    WIRE.  435 

battery  current  on  breaking  contact  acquires  sufficient  intensity 
to  communicate  powerful  shocks  and  give  vivid  sparks.  This 
is  conclusively  proved  by  the  following  experiments :  a  very 
small  compound  battery  was  formed  of  six  pieces  of  copper 
bi'll-wire,  each  about  1J  inches  long,  and  six  pieces  of  zinc 
of  the  same  size,  a  battery  altogether  too  small  to  give  the 
slightest  shock  or  the  faintest  spark  when  the  poles  were  con- 
nected: the  connection  between  the  poles  was  then  made  by 
means  of  a  fine  copper  wire  one-sixteenth  of  an  inch  in  diam- 
eter, thoroughly  insulated  by  a  cotton  covering,  five  miles  in 
length,  and  wound  upon  a  small  core  of  soft  iron :  the  sho.-k  on 
breaking  connection  between  the  poles,  with  this  arrangement 
of  the  conducting  wire,  was- distinctly  felt  at  the  same  moment 
by  twenty-six  persons,  who  had  formed  a  circle  by  joining  hands 
arid  were  placed  in  such  a  manner  as  to  form  a  part  of  tlie  gal- 
vanic circuit:  the  shock  felt  by  the  sam 3  persons  01  making 
contact  with  the  battery,  was  hardly  perceptible.  A  current  is 
likewise  produced  when  contact  is  made,  but  it  is  by  no  means 
as  powerful,  and  is  in  a  direction  opposite  to  that  of  the  ba'teiy. 
A  thermo-electric  battery  which  is  ordinarily  too  weak  to  fur- 
nish sparks,  can  be  made  to  do  so  on  breaking  contact,  by  means 
of  a  coil  wound  upon  an  iron  axis.  In  the  case  of  the  largs 
magnetic  helix  constructed  by  Dr.  Page,  described  in  §426, 
the  length  of  the  terminal  secondary  or  separation  spark,  when 
the  battery  current  was  broken  was  immense :  when  the  bat- 
tery was  allowed  to  attain  its  full  power,  the  sudden  separation 
of  the  wires  produced  sparks  eight  inches  in  leng  h :  when  the 
separation  was  slow,  the  sparks  were  short  and  spread  out  more 
like  flame.  The  effect  is  still  further  increased  if  the  soft  iron, 
instead  of  being  solid,  consists  of  a  bundle  of  straight  wires. 
To  observe  the  effects  of  the  induced  extra  current  in  the 
primary  wire,  suitable  wires  may  be  attached  at  A  and  c,  Fig. 
217,  in  place  of  the  galvanometer:  and  thus  it  may  be  shown 
that  this  direct  extra  current  gives  violent  shocks  and  bright 
sparks,  decomposes  water,  melts  platinum  wire,  and  magnetizes 
steel  needles.  The  brilliancy  of  the  spark  is  much  increased 
by  employing  a  ribbon  of  sheet  copper  coiled  into  a  spiral,  in- 
stead of  a  helix  of  insulated  wire.  There  is  a  difference  in 
the  character  of  the  extra  current  when  a  coil  of  fine  wire  is 
employed,  from  that  which  is  produced  with  a  ribbon  coil.  In 


What  was  the  length  of  the  spark  produced  by  Dr.  Page's  large  helix  ?  What  is  the 
effect  of  substituting  iron  wires  for  the  solid  iron  rod  ?  IIosv  may  the  effects  of  the  in- 
duced ext-a current  in  the  primary  wire  be  displayed?  What  are  tliese  effects ?  What 
is  tue  effect  of  substituting  a  coil  of  tine  wire  for  a  ribbon  coil? 


436  INDUCED    TERTIARY    CURRENTS. 

the  former  case,  it  is  more  intense,  gives  more  violent  shocks, 
and  effects  chemical  decomposition  more  rapidly :  in  the  latter, 
it  is  of  greater  quantity,  gives  more  vivid  sparks,  and  exerts 
greater  heating  power.  These  direct  and  inverse  extra  cur- 
rents, produced  when  the  connection  of  the  primary  wire  is 
broken  or  made,  are  not  confined  to  the  wire,  but  extend 
through  the  whole  series  of  the  battery,  and  increase  in  rower 
with  the  extent  of  the  series.  They  are  probably  due  to  the 
sudden  polarization  and  discharge,  §312,  of  all  the  molecules 
in  the  secondary  circuit,  on  completing  connection,  and  to  the 
sudden  de-polarization  and  discharge  in  the  opposite  direction, 
on  breaking  connection.  It  will  be  remembered  that  they  do 
not  exist,  so  long  as  the  primary  current  circulates  continu- 
ously through  the  battery.  They  spring  into  action  momen- 
tarily only,  the  instant  this  continuity  is  interrupted. 

440.  Induced  Tertiary  currents.  Induced  currents  of 
higher  orders.  Henry's  Coils.  The  secondary  current  which 
is  induced  by  the  primary  current  of  the  battery,  may  be  used  to 
induce  a  tertiary  current,  and  this  tertiary  a  quaternary  current, 
and  so  on.  Thus,  in  Fig.  218,  let  L,  represent  one  cell  of 
Daniell's  battery,  and  A,  a  primary  coil  of  copper  ribbon  carry- 
ing the  battery  current:  let  the  secondary  coil  be  placed  imme- 
diately over  it,  and  its  two  extremities  be  extended  so  as  to 
connect  with  the  extremities  of  a  third  coil,  B  :  these  two  coils 
will  in  effect  form  a  closed  circuit,  and  constitute  but  one  second- 
ary circuit :  then  immediately  above  B,  let  another  ribbon  coil 
be  placed,  whose  extremities  are  extended  so  as  to  connect 
with  the  coil  c :  these  two  coils  will  in  effect  form  but  one 
closed  circuit  carrying  the  tertiary  current :  immediately  above 
c,  let  another  ribbon  coil  be  placed  whose  extremities  are  ex- 
tended so  as  to  connect  with  those  of  the  coil  D  :  these  two 
coils  will  in  effect  ibrm  but  one  closed  circuit  carrying  the 
quaternary  current :  immediately  above  D,  let  another  ribbon 
coil  be  placed  the  extremities  of  which  are  connected  with  the 
galvanometer  G:  these  two  coils  will  in  effect  form  but  one  cir- 
cuit carrying  the  quinquenary  current.  When  the  connection 
of  the  primary  coil  A,  with  the  battery  is  formed  or  broken, 
a  current  will  be  induced  simultaneously  in  all  the  coils,  but 
inversely  in  each  pair.  Thus,  if  the  connection  of  the  coil  A, 
with  the  battery  be  completed,  a  secondary  current  of  negative 
electricity  will  be  induced  in  the  coil  B  ;  a  tertiary  current  of  pos- 

440.  Sho-^hovv  induced  tertiary  currents  may  be  produced  :  current  of  h-'^her  orders. 
State  tiio  relations  of  these  currents  when  the  coui>ectiou  with  the  batter/  u  cstu.bli.hed : 


HENRY  S    COILS. 


437 


FiS  218-  itive  electricity,  moving  in  the  opposite 

direction,  in  c ;  a  quaternary  current 
of  negative  electricity,  moving  in  the 
same  direction,  in  D ;  and  a  quinquen- 
ary  current  of  positive  electricity,  mov- 
ing in  the  opposite  direction,  in  the  last 
coil,  as  shown  by  the  galvanometer. — 
On  breaking  the  connection  of  the  pri- 
mary coil  with  the  battery,  currents 
will  be  induced  simultaneously  in  all 
the  coils,  but  in  the  inverse  direction ; 
in  the  secondary  coil  they  will  be  posi- 
tive, in  the  tertiary  negative,  in  the 
quaternary  positive,  in  the  quinquenary 
negative.  By  an  extension  of  the  se- 
ries, currents  even  of  the  ninth  order 
have  been  obtained,  the  successive  cur- 
rents being  alternately  positive  and 
negative,  direct  and  inverse.  These 

jji  m  coils  are  generally  called  Henry's 
coils,  after  Prof.  Henry  who  first  in- 
vestigated this  subject.  They  can  be 
made  to  give  currents  of  quantity  or 
intensity,  according  as  they  are  com- 
posed of  copper  ribbon  or  a  great 
length  of  fine  insulated  wire.  The  two 
currents,  direct  and  inverse,  through- 
out the  whole  series,  are  exactly  equal 
in  quantity.  They  can  be  induced 
even  if  the  coils  are  con.-iderably  sep- 
arated from  each  other,  though  the  ef- 
fect is  diminished  by  distance,  and 

il«  even  when  glass  plates  are  inter- 
posed, but  they  are  destroyed  by  the 
interposition  of  a  plate  of  metal  in  any 
part  of  the  series.  They  progressively 
diminish  in  energy  from  the  beginning 
to  the  end  of  the  series.  The  tertiary 
currents  may  be  very  satisfactorily  ex- 
hibited by  introducing  a  second  double 
helix,  in  Fiq.  214,  between  r,  and  the 

Henry's   Coils.  J 


when  it  is  broken.   By  waom  was  the  discovery  made?    Give  the  history  of  the  discovery. 


438  DISCOVERY    OF    THE    EXTRA    CURRENT. 

battery,  and  connecting  the  outer  helix  of  the  second  pair,  with 
the  inner  helix,  p,  of  the  first ;  on  every  completion  and  break 
of  the  battery  circuit,  a  secondary  current  will  circulate  in  p, 
and  a  tertiary  current  in  the  opposite  and  in  the  same  direc- 
t'ons  alternately,  will  be  induced  in  the  outer  coil,  s,  as  shown 
by  the  galvanometer.  Shocks  may  also  be  obtained,  which 
may  be  increased  by  placing  a  bundle  of  iron  wires  within  the 
helix,  as  shown  in  Fig.  222.  In  the  following  table  the  direc- 
tion of  the  successive  induced  currents,  both  at  the  establishment 
and  break  of  the  battery  current  are  given :  the  sign  +  indi- 
ca:ing  those  which  flow  in  the  same  direction  as  the  battery  cur- 
rent, and  the  sign  —  those  that  flow  in  the  opposite  direction. 

Table  of  the  directions  of  the  induced  currents^  up  to  the  ninth  order. 

At  the  beginning         At  the  ending. 

Primary  current,        +  -+- 

Secondary,        + 

Tertiary, -f-  — 

Quaternary, —  + 

Quinquenary, -+-  — 

Sextenary, 4. 

Septenary, -|- 

Eighth  order, —  4- 

Ninth  orderj + 

441.  History  of  the  discovery.  This  induction  of  a  second- 
ary current  in  the  primary  wire  itself,  the  peculiar  action  of 
a  long  conducting  wire,  either  straight  or  coiled  into  a  helix, 
and  the  increase  of  effect  obtained  by  a  ribbon  of  sheet  copper, 
were  discovered  in  1831,  by  our  countryman,  Prof.  Henry,  now 
of  the  Smithsonian  Institute,  and  published  in  the  22d  volume 
of  Silliman's  Journal.  The  investigation  was  continued  by  him 
in  1834,  and  the  results  were  communicated  to  the  American 
Philosophical  Society  of  Philadelphia,  January  16th,  1835,  and 
were  published  in  a  circular  of  thai  Society  dated  Feb.  1835, 
and  reprinted  in  the  Journal  of  the  Franklin  Institute,  vol.  XV. 
The  same  discovery  was  also  made  by  Mr.  Faraday,  his  atien- 
tion  having  been  called  to  the  primary  fact  of  the  increase  of 
effect  produced  by  using  a  long  wire,  and  especially  one  wound 
round  an  electro-magnet,  to  connect  the  poles  of  a  battery,  by  a 
young  man  named  Willam  Jenkin,  and  was  communicated  by 
him  to  the  Royal  Society  in  a  paper  received  Dec.  18th,  1834, 
and  read  January  29th,  1835,  entitled  "On  the  influence  by 
inductron  of  the  electric  current  upon  itself."  In  this  paper 
many  new  facts  were  given,  but  the  credit  of  the  original  discov- 
ery in  1831,  clearly  belongs  to  Prof.  Henry. 


MAGNETO-ELECTRIC 


§  V.    Magneto-Electricity. 


439 


442.  Blao-neto-electric  Induction.  The  induction  of  a 
current  of  electricity  is  not  limited  to  the  primary  current  of  the 
battery :  a  similar  current  is  also  induced  by  the  action  of  a 
permanent  magnet  upon  a  closed  wire,  and  also  by  the  action 
of  an  electro-magnet  actuated  by  a  primary  battery  current. 
The  former  is  called  Magneto-electric  induction ;  the  latter, 
Volta-magneto-electric  induction.  In  the  case  of  magneto-elec- 
tric induction,  the  conditions  necessary  to  induce  the  secondary 
current,  are  as  follows.  There  must  be  a  closed  circuit,  with  a 
galvanometer  included  for  the  purpose  of  indicating  the  exist- 
ence of  the  current,  as  in  the  case  of  volta-electric  induction, 
§433,  and  then  a  strong  magnet  must  be  rapidly  brought  near, 
and  removed  from  the  closed  wire.  Thus,  in  Fig.  219,  a  contin- 

Fig.  219. 


Magneto-Electric  Induction. 

uous  wire,  carefully  insulated  by  silk,  is  wound  into  a  helix,  and 
itts  two  ends  are  connected  wifh  a  galvanometer  in  such  a  way 
as  to  form  a  closed  circuit.  On  introducing  a  powerful  magnet 
into  the  interior  of  the  helix,  which  is  made  hollow  for  this  pur- 
po-e,  the  needle  experiences  a  violent  deflection,  showing  the 

442,  What  is  Electro-magnetic  induction  ?  What,  is  Volta-electric  induction  ?  IIo\r 
can  the  induction  of  electricity  by  a  magnet  be  proved  ?  Describe  the  experiments. 
Why  must  the  magnet  not  be  iutroduced  more  than  half  way  ? 


440  INDUCTION. 

production  of  a  current  of  electricity  in  the  inverse  direction 
from  that  which  is  circulating  around  the  magnet,  according 
to  the  theory  of  M.  Ampere,  §404.  The  magnet  beincr  allowed 
to  remain  motionless  in  the  helix,  in  a  few  moments  the  needle 
resumes  a  stable  position;  but  if  the  magnet  be  rapidly  with- 
drawn from  the  helix,  the  needle  is  immediately  deflected, 
and  indicates  an  electrical  current  in  the  wire  the  reverse  of 
the  previous  one,  but  in  the  same  direction  as  that  in  the  mag- 
net. If  the  magnet,  instead  of  being  placed  within  the  helix, 
be  merely  passed  over  it  rapidly,  the  effect  is  the  same.  It  is 
also  found  that  in  performing  these  experiments  care  must  be 
taken  not  to  introduce  the  magnet  more  than  half  way  into  the 
he!ix ;  for  if  passed  wholly  through  at  one  motion,  the  galvan- 
ometer needle  is  deflected,  is  then  suddenly  stopped  as  by  a 
blow,  and  finally  is  deflected  in  the  opposite  direction  :  the  move-' 
inent  of  the  needle  is  reversed  because  as  the  magnet  advances 
and  appears  at  the  opposite  extremity  of  the  coil,  it  comes  at 
last  to  produce  the  same  effect  as  withdrawing  a  magnet  from  a 
helix,  when,  as  ha^  been  stated,  a  current  the  reverse  of  the 
first  is  produced.  It  is  abo  found  that  the  two  poles  of  the 
magnet  produce  currents  in  opposite  directions,  i.  e.,  if  the  north 
pole,  on  being  introduced  into  the  helix,  produces  a  current  from 
left  to  right  as  shown  by  the  galvanometer,  the  south  pole,  on 
b^ing  introduced  into  the  same  helix,  will  induce  a  current  in 
the  opposite  direction,  or  from  right  to  left.  It  is  also  found, 
that,  the  pole  of  the  magnet  remaining  the  same,  the  winding 
of  the  coil  to  the  right  or  the  left,  reverses  the  direction  of  the 
current:  thus,  when  the  north  pole  of  a  magnet  is  introduced 
into  a  right-hand  helix,  the  induced  current  as  shown  by  the 
galvanometer,  will  be  in  the  inverse  direction  to  that  which  is 
induced  when  the  same  pole  is  introduced  into  a  left-hand  helix. 
443.  Electricity  also  Induced  by  Induced  Magnetism. 
The  same  effect  may  be  produced  by  the  rapid  making  and 
unmaking  of  a  magnet  by  means  of  induction.  If  a  piece  of 
soft  iron  be  introduced  into  the  helix,  Fig.  219,  instead  of  a 
permanent  magnet,  and  a  powerful  bar  magnet  be  brought 
near  the  piece  of  soft  iron,  so  as  to  induce  magnetism  in  it, 
we  find  the  same  result  produced  as  would  be  if  a  perma* 
nent  magnet,  having  similar  poles,  were  introduced  into  the 
helix.  In  Fig.  220,  if  N,  s,  be  a  powerful  horse-shoe  magnet, 
and  w,  5,  be  a  piece  of  soft  iron  having  a  short  piece  of  insulated 

What  is  the  inductive  effect  of  the  opposite  poles  ?  What  is  the  effect  of  reversing  the 
winding  of  the  coil? — 443.  Hosv  may  electricity  he  induced  by  induced  magnetism? 
How  cau  an  electric  spark  be  obtained  from  a  magnet?  Describe  Figs.  22.0  aud  2i,l. 


ELECTRICITY    INDUCED 

Fig.  220. 


441 


The  Electric  Spark  obtained  from  a  Magnet. 

wire  wound  around  it,  the  two  ends  of  which,  a,  5,  are  brought 
together  so  as  to  nearly  touch,  then,  whenever  the  piece  of  soft 
iron,  w,  s,  is  brought  down  on  the  magnet  and  becomes  magnet- 
ized by  induction,  a  current  of  electricity  is  generated  in  the  coil, 
and  a  bright  spark  flashes  between  the  extremities,  a,  b:  a  sim- 
ilar spark  takes  place  whenever  the  soft  iron  bar  is  raised  from 
the  magnet  and  its  induced  magnetism  disappears.  Again,  if  c 
ill  Fig.  221,  be  a  bar  of  soft  iron,  curved  and  wound  with  wire, 
the  two  extremities  of  which  are  con- 
nected with  a  galvanometer,  placed  at 
some  distance,  and  not  seen  in  the  figure, 
on  bringing  the  powerful  horse-shoe 
magnet,  N,  s,  rapidly  near  the  extremi- 
ties, A,  B,  of  the  >coft  iron,  the  bar  C 
immediately  becomes  magnetized  by  in- 
duction, and  at  that  instant  a  powerful 
deflection  is  made  in  the  needle  by  the 
electrical  current  induced  in  the  wire: 
the  needle  soon  regains  its  equilibrium, 
but  the  instant  that  N,  S,  is  removed,  and 
Etectnr.it  i/ 1 miitwi  by  induced  c  ceases  to  be  magnetized  by  induction. 

Magnetism.  J 


442  BY   INDUCED    MAGNETISM. 

t 

there  is  a  second  violent  deflection  of  the  needle,  showing  the 
production  of  a  current  of  electricity  in  the  opposite  direction. 
444.     History  of  the    discovery  of   Magneto-electricity. 

The  induction  of  electricity  by  magnetism  was  the  discov- 
ery of  Mr.  Faraday,  in  1831.  His  original  experiment  was 
arranged  as  follows. — "  A  combination  of  helices  like  that  al- 
ready described,  §434,  was  constructed  upon  a  hollow  cylinder 
of  pasteboard  ;  there  were  eight  lengths  of  copper  wire,  contain- 
ing altogether  220  feet :  all  the  similar  ends  of  the  compound 
ho  low  helix  were  bound  together  by  copper  wire,  forming  two 
terminations,  and  these  were  connected  with  the  galvanometer. 
One  end  of  a  cylindrical  magnet,  three-quarters  of  an  inch  in 
diameter  and  eight  inches  and  a  half  in  length,  was  introduced 
into  the  axis  of  the  helix,  and  then,  the  galvanometer  needle 
having  become  stationary,  the  remainder  of  the  magnet  was 
suddenly  thrust  in ;  the  needle  was  immediately  deflected  in 
the  manner  in  which  it  ought  to  be  according  to  Ampere's  the- 
ory :  being  left  in,  the  needle  resumed  its  former  posit'on,  and 
then,  the  magnet  being  withdrawn,  the  needle  was  deflected  in 
the  opposite  direction  :  these  effects  were  not  great,  but  by  intro- 
ducing and  withdrawing  the  magnet  so  that  the  impulse  each 
time  should  be  added  to  those  primarily  communicated  to  the 
needle,  the  latter  could  be  made  to  vibrate  through  an  arc  of 
180°  or  more.  In  this  experiment,  the  magnet  must  not  be 
passed  entirely  through  the  helix,  for  then  a  second  action 
occurs.  When  the  magnet  is  introduced,  the  galvanometer 
needle  is  deflected  in  a  certain  direction ;  but  being  in,  whether 
pushed  quite  through  or  withdrawn,  the  needle  is  deflected  in  a 
direction  the  reverse  of  that  previously  produced.  When  the 
magnet  is  passed  in  and  through  at  one  continuous  motion,  the 
needle  moves  one  way,  is  then  suddenly  stopped,  and  finally 
moves  the  other  way." — "  Similar  effects  were  then  produced  by 
the  sudden  induction  of  magnetism  in  soft  iron.  A  soft  iron 
cylinder  was  introduced  info  the  axis  of  the  hol'ow  helix:  a 
counle  of  bar  magnets,  each  twenty-four  inches  long,  were  ar- 
ranged with  their  opposite  poles  in  contact  at  one  end,  and  then 
spread  out  ?o  that  their  other  poles  might  be  put  in  contact 
with  the  extremities  of  the  soft  iron  cylinder,  one  pole  being  at 
one  extremity  of  the  helix,  and  the  other  at  the  other  extremity, 
so  as  to  embrace  the  iron  core,  and  convert  it  into  a  magnet  by 
induction :  on  breaking  contact,  or  reversing  the  poles,  the  mng- 

444.  Who  discovered  the  induction  of  electricity  by  magnetism  ?    Describe  his  origi- 
nal experimeut.    How  were  the  helices  arranged  1 


ELECTRICITY   INDUCED    BY    AN    ELECTRO-MAGNET.      443 

netism  was  destroyed  or  reversed  at  pleasure.  On  making 
contact,  the  needle  was  deflected ;  continuing  contact,  the  needle 
became  indifferent,  and  resumed  its  first  position :  on  breaking 
contact,  it  was  again  deflected,  but  in  the  opposite  direction  to 
the  first  effect,  and  then  it  became  indifferent :  when  the  mag- 
netic contacts  were  reversed,  the  deflections  were  reversed." 

445.  An  Electro-magnet  magnetized  and  de-magnetized, 
will  induce  Electricity  in  a  closed  Wire.— Volta-magneto-elec- 
tric  Induction.  In  like  manner,  if,  in  Fig.  214,  intended  to 
illustrate  Volta-electric-induction,  a  bar  of  soft  iron  be  intro- 
duced into  the  centre  of  the  primary  coil,  then,  on  establishing 
connection  with  the  battery,  not  only  is  there  a  secondary 
current  produced  in  the  outer  coil,  on  completing  and  breaking 
the  circuit  in  the  primary  coil,  but  also  an  additional  secondary 
current  in  the  same  direction  as  the  first,  by  the  magnetization 
and  de-magnetization  of  the  bar  of  soft  iron,  which  takes  place, 
whenever  the  connection  of  the  inner  coil  with  the  battery  is 
made  and  broken.  The  strength  of  this  induced  current  will 
be  proportioned  to  the  power  of  the  battery,  to  the  length  and 
fineness  of  the  secondary  wire,  and  also  to  the  size  of  the  soft 
iron  rod  employed,  and  the  power  of  the  electro-magnet  pro- 
duced. The  power  of  an  electro-magnet,  other  things  being 
equal,  depending  upon  the  extent  of  surface  which  it  presents, 
if  the  bar  employed  be  very  small,  and  introduced  only  a  short 
distance,  only  a  feeble  electro-magnet  will  be  produced,  and  a 
comparatively  feeble  secondary  current  generated.  If  the  rod 
be  large,  and  introduced  to  the  extreme  end  of  the  coil,  its  elec- 
tro-magnetic power  will  be  proportionately  increased,  and  also 
the  strength  of  the  secondary  current.  A  bundle  of  wires  is 
found  to  produce  much  greater  effect  than  a  Folid  iron  ro;l,  and 
this  is  proportioned  to  the  number  of  the  wires  employed. 
This  affords  a  very  convenient  mode  of  regulating  the  power 
of  the  secondary  current ;  commencing  with  one  wire,  the 
strength  of  the  induced  current  will  be  increased  by  every  suc- 
cessive wire  that  is  added.  Thus,  in  Fig.  222,  if  p  represent 
the  primary  coil,  s  the  secondary  coil,  and  G  the  galvanometer, 
the  strength  of  the  secondary  current  induced  by  making  and 
breaking  contact  with  the  battery,  will  be  greatly  increased 
with  the  addition  of  every  wire  that  is  introduced  into  P,  indi- 
cated by  the  deflection  of  the  needle  and  strength  of  the  shocks. 

445  What  is  the  effect  of  making  and  unmaking  an  electro-magnet  within  a  helix  ? 
What  is  the  effect  of  increasing  the  size  of  the  soft-iron  core?  of  using  wires  i  ist«-ad  of 
an  iron  rod  ?  Describe  Fig.  222  How  can.  the  strength  of  the  shocks  be  regulated '! 


444 


The  strength  of  the  Induced  Current  proportioned  to  the  number  of  wires  employed. 

If  a  bar  of  copper  were  introduced  into  the  coil,  instead  of  an 
iron  bar,  or  wires,  the  current  would  not  be  stronger  than  if  the 
two  coils  alone  were  employed.  Thus  we  may  make  use  of  the 
electricity  of  the  primary  coil  to  induce  both  electricity  and 
magnetism,  and  then  employ  the  magnetism  so  induced  to  add 
to  the  force  of  the  induced  secondary  current  of  electricity. 

446.  History  of  the  discovery  of  the  Induction  of  electric- 
ity by  Electro-mag-netism.  This  was  also  the  dis<  overy  of  Mr. 
Faraday,  in  1831.  His  original  experiment  was  arranged  as 
follows. — "A  welded  ring,  Fig.  223,  was  made  of  soft  round  bar- 
iron,  metal  being  seven-eighth's  of  an 
inch  in  thickness,  and  the  rinjr  six 
inches  in  external  diameter.  Three 
helices  were  put  round  one  part  of 
this  ring,  each  containing  about  twen- 
ty-four feet  of  copper  wire,  l-20th 
of  an  inch  thick  :  they  were  insulated 
from  the  iron  and  from  each  other, 
and  superimposed,  occupying  about 
nine  inches  in  length  upon  the  ring, 
or  somewhat  less  than  one-half  of 
the  circumference:  they  were  arranged  so  as  to  be  u?ed  sepa- 
rately or  conjointly.  On  the  other  half  of  the  ring  about  sixty 


Fctraday^s  Magneto-Electric 
Ring. 


44<v  Who  discovered  the  induction  of  electricity  by  electro-magnetism  1    Describe  his 
original  experiment.    liow  were  the  helices  wound  upon  the  iron  ring? 


OF    THE    DISCOVERY.  445 

feet  of  similar  copper  wire,  in  two  pieces,  were  applied  in  the 
same  manner,  also  carefully  insulated  from  the  iron  and  from 
each  other,  and  forming  a  helix  which  had  the  same  common 
direction  with  the  former  helices,  but  separated  from  them  by 
about  half  an  inch  of  the  uncovered  iron  at  each  extremity,  M,  M. 
This  latter  helix,  a,  &,  was  connected  by  copper  wires  with  a 
galvanometer,  three  feet  from  the  ring,  so  as  to  constitute  a 
closed  circuit.  The  first  helices,  c,  d,  were  then  united,  end 
to  end,  so  as  to  form  one  common  helix,  the  extremities  of  which 
were  connected  with  a  battery  of  ten  pairs  of  plates,  four  inches 
square.  The  galvanometer  was  immediately  affected,  and  to 
a  much  greater  degree  than  when  a  battery  of  helices  of  ten- 
fold power,  not  wound  round  soft,  wire,  were  employed :  but, 
although  the  connection  with  the  battery  was  continued,  the 
effect  was  not  permanent,  for  the  galvanometer  needle  soon 
came  to  rest  in  its  natural  position,  as  if  quite  indifferent  to  the 
attached  electro-magnetic  arrangement.  Upon  breaking  con- 
nection with  the  battery,  the  needle  was  again  powerfully  de- 
flected, but  in  the  contrary  direction  to  that  induced  in  the  first 
instance.  Upon  arranging  the  apparatus  so  that  the  last  helix 
should  be  thrown  out  of  action,  and  connecting  the  galvanom- 
eter with  one  of  the  three  helices  of  the  first  series,  the  other 
two  being  separated  from  it  and  joined  together,  so  as  to  form 
one  helix,  and  connecting  this  with  the  battery,  similar,  but 
rather  more  powerful,  effects,  were  produced  upon  the  galvan- 
ometer needle.  When  the  battery  current  was  sent  through 
the  helix  in  one  direction,  the  galvanometer  needle  was  deflected 
on  the  one  side;  if  sent  through  in  the  other  direction,  the  de- 
flection was  on  the  other  side.  The  deflection  on  breaking  the 
connection  with  the  battery,  was  always  th^  reverse  of  that  pro- 
duced on  completing  it.  On  making  contact,  the  deflection 
always  indicated  an  induced  current  moving  in  the  opposite 
direction  to  that  of  the  battery,  but  on  breaking  confact,  the 
deflection  indicated  an  induced  current  moving  in  the  same 
direction  as  that  of  the  battery.  No  continuance  of  the  battery 
current  caused  any  deflection  of  the  galvanometer  needle.  No 
making  or  breaking  connection  on  the  galvanometer  side  of  the 
arrangement,  produced  any  effect  on  the  needie.  Upon  using 
the  power  of  o  le  hundred  pairs  of  plates  with  this  ring,  the 
impulse  when  contact  wa>  completed  or  broken,  was  so  great  MS 
to  make  the  needle  spin  round  rapidly  four  or  five  times,  before 

What  was  the  effect  on  forming  connection  with  the  battery  ?  on  breaking  connection  ? 
on  reversing  the  current?  What  was  the  second  arrangement?  Which  was  found  to 
be  the  most  powerful  ? 


446  ARAGO'S 

its  motion  was  reduced  to  mere  oscillation,  by  1he  operation 
of  the  air  and  terrestrial  magnetism.  Another  arrangement  was 
then  employed,  connecting  our  former  experiments  on  Volta- 
electric  induction  with  the  present.  A  combination  of  helices 
like  those  already  described,  §434,  was  constructed  upon  a 
hollow  cylinder  of  paste-board :  there  were  eight  lengths  of 
copper  wire,  containing  altogether  about  220  feet ;  four  of  these 
helices  were  then  connected  end  to  end,  and  then  with  the  gal- 
vanometer :  the  other  intervening  four  were  also  connected  end 
to  end,  and  the  battery  of  one  hundred  pairs  discharged  through 
them.  In  this  form,  the  effect  on  the  galvanometer  was  hardly 
sensible,  although  magnets  could  be  made  by  the  induced 
current.  But  when  a  soft  iron  cylinder,  seven-eighths  of  an 
inch  thick  and  twelve  inches  long,  was  introduced  into  the 
paste-board  tube,  surrounded  by  the  helices,  then  the  induced 
current  affected  the  galvanometer  powerfully,  and  with  all  the 
phenomena  just  described :  it  possessed  also  the  power  of 
making  magnets  apparently  with  more  energy  than  when  no 
iron  cylinder  was  present.  When  the  iron  cylinder  was  re- 
placed by  an  equal  cylinder  of  copper,  no  effect  beyond  that  of 
the  helices  alone  was  produced.  The  iron  cylinder  arrangement 
was  not  so  powerful  as  the  ring  arrangement  already  described." 
447.  A  Mag-net  will  induce  Electricity  in  a  body  in  mo- 
tion :  and  a  IKEagnet  in  motion  will  induce  Electricity  in  a 
body  at  rest.— Arag-o's  Rotations-  If  a  circular  disc  of  cop- 
per, M,  Fig.  224,  be  made  to  revolve  with  great  rapidity  beneath 


Fig.  224. 


Arago's  Rotations. 


a  magnetic  needle,  w,  s,  supported  upon  a  flat  piece  of  gla^c  and 
in  the  same  horizontal  plane,  the  needle  will  be  deflected  in  the 

447.  What  is  the  effect  of  a  magnet  upon  a  body  in  motion  ?  of  a  magnet  in  motion 
Upon  a  body  at  rest  ? 


ROTATIONS.  447 

direction  of  the  motion,  and  stop  from  20°  to  30°  out  of  the 
direction  of  the  magnetic  meridian,  according  to  the  veloc'ty 
of  the  motion.  If  the  velocity  be  increased,  the  needle  is  ulti- 
mately deflected  more  than  90° :  it  is  then  carried  beyond  this 
point,  describes  an  entire  revolution,  and  finally  follows  the  mo- 
tion, of  the  disc  until  this  ceases.  Conversely,  if  a  horse-shoe 
magnet  placed  vertically  be  made  to  rotate  below  a  copper  disc 
suspended  on  untwisted  silk  threads,  the  disc  will  rotate  in 
the  same  direction  as  the  magnet.  The  effect  decreases  with 
the  distance  of  the  disc,  and  varies  with  the  material :  the  great- 
est effect  is  produced  by  the  metals ;  with  wood,  glass  and  water, 
it  disappears:  if  the  action  on  copper  be  represented  by  100, 
that  on  other  metals  is  as  follows:  zinc  95,  tin  46,  lead  25,  anti- 
mony 9,  bismuth  2 :  if  the  disc  be  slit  in  the  direction  of  the 
radius,  the  effect  is  much  reduced,  but  is  restored  if  a  connection 
be  completed  again  by  soldering.  These  rotations  were  first 
observed  by  M.  Arago,  in  1825,  after  whom  they  have  been 
named.  He  also  noticed  that  the  presence  of  a  mass  of  unmag- 
netic  metal,  like  copper  at  re>t,  diminishes  the  number  of 
oscillations  which  a  magnetic  needle  make^  in  a  given  time  :  in 
the  case  of  copper,  the  number  is  reduced  from  3uO  to  4.  Mr. 
Faraday,  in  1831,  observed  the  converse  of  this,  viz:  that  the 
presence  of  a  magnet  at  rest  diminishes  the  motion  of  a  rotating 
mass  of  metal,  and  finally  destroys  it :  if  a  cube  of  copper  be 
suspended  by  a  twisted  thread,  so  as  to  rotate  rapidly  between 
the  poles  of  an  unactuated  electro-magnet,  it  stops,  the  instant 
the  electro-magnet  is  excited  by  the  battery  current.  These 
facts  were  first  explained  by  Mr.  Faraday,  in  183 1 .  He  showed 
that  they  are  due  to  the  secondary  electrical  currents  which  are 
induced  in  the  discs  of  metal  by  the  action  of  magnets,  either 
the  metal  or  the  magnet  being  in  motion.  He  found  in  all  cases, 
that  whenever  a  plate  of  conducting  metal  is  made  to  pass 
either  before  a  single  pole,  or  the  opposite  poles,  of  a  magnet, 
so  as  to  cut  the  magnetic  curves  at  right  angles,  electrical  cur- 
rents are  produced  in  the  metal  at  right  angles  to  the  direction 
of  the  motion :  in  the  case  of  the  revolving  disc,  the  direction  of 
these  currents  is  from  the  centre  to  the  circumference,  following 
the  direction  of  the  radii :  it  is  to  the  operation  of  these  induced 
currents,  that  the  effects  in  question  are  due.  The  magnetic 
curves  here  spoken  of,  are  curved  lines  of  magnetic  force  which 
pass  through  the  axis  of  a  magnet,  or  the  line  joining  the  poles, 

Describe  Arago's  rotations.     Give  Mr.  Faraday's  explanation.     What  are  the  magnetic 
curves? 


448 


MAGNETO-ELECTHIC    INDUCTION 


The  Magnetic  Curves. 


FiS-  -25-  and  in  the  same  plane 

with  this  line,  Fig.  225. 
Whenever  these  curved 
lines  of  magnetic  force 
are  cut  by  the  move- 
ment across  them  of 
any  mass  of  matter 
which  is  an  electrical 
conductor,  as  a,  b,  in 
the  Fig.)  whether  it  be 
a  disc,  a  mass  of  metal; 
or  a  wire,  induced  sec- 
ondary currents  of  electricity  are  produced. 

448.  The  Magnetism  of  the  Earth  induces  secondary 
currents  of  Electricity  in  metallic  bodies  in  motion.  Terres- 
trial magnetism,  acting  like  an  immense  magnet  placed  in  the 
earth,  occupying  the  direction  of  the  dipping  needle,  and 
according  to  Ampere's  theory,  §403,  operating  like  a  series  of 
electrical  currents,  flowing  from  east  to  west  parallel  to  the 
magnetic  equator,  will  develop  induced  electrical  currents  in 
wires  or  metallic  bodies  that  are  moved  across  the  magnetic 
axis  of  the  earth  parallel  to  the  equator,  and  cutting  the  mag- 
netic curves.  This  was  proved  in  1831,  by  Mr.  Faraday,  by 
placing  a  long  helix  of  copper  wire  covered  with  silk,  in  the 
p!ane  of  the  magnetic  meridian,  directed  towards  the  magnetic 
pole  of  the  earth,  and  parallel  to  the  dipping  needle :  by  turning 
this  helix  180°  degrees  around  its  longitudinal  axis,  so  as  to 
revolve  the  strands  of  the  helix  across  the  magnetic  meridian, 
he  observed  that  at  each  turn,  a  galvanometer  connected  with 
the  two  ends  of  the  helix,  was  deflected,  showing  the  passage  of 
an  electric  current.  The  same  effect  is  always  produced  by 
moving  a  wire,  who-e  ends  are  connected  with  a  delicate  galvan- 
ometer, at  right  angles  across  the  magnetic  meridian.  This 
was  beautifully  demonstrated  in  laying  the  Atlantic  cable  at  the 
bottom  of  the  ocean,  in  a  direction  about  due  east  and  west :  as 
the  irregular  motion  of  the  steamship  produced  by  the  waves, 
drew  the  cable  back  and  forth  across  the  magnetic  meridian, 
the  secondary  electrical  current  which  it  induced,  inconceivably 
faint  as  it  must  have  been,  produced  a  perceptible  deviation  of 
the  mirror  and  the  spark  of  reflected  light  in  the  reflecting  gal- 
vanometer, §418,  at  Valentia;  so  that  it  was  literally  true  that 


Wlint  effect  has  the  magnetism  of  the  earth  upon  metallic  bodies  in  motion?    How 
Was  tuis  illustrated  iu  la^iug  tne  Atlantic  cable?  -  • 


,  CONFIRMS  AMPERE'S  THEORY.        449 

they  knew  at  Valentia  every  time  the  Great  Eastern  rolled. 
In  this  case,  the  ocean  itself  formed  a  part  of  the  electrical  cir- 
cuit, together  with  the  cable  wire,  and  rendered  it  complete. 

•£49.  lYIajncto-clectric  Induction  supports  Ampere  s  the- 
ory. The  induction  of  electricity  by  the  magnet  is  exac:ly 
wh  it  might  be  expected  if  Ampere's  theory  be  true,  §403,  4J4, 
and  confirms  it.  If,  as  is  supposed  by  Ampere,  magnetism  is 
proluced  by  a  series  of  electric  currents  perpetually  circulating 
around  a  magnet  in  a  direction  at  right  angles  to  its  ax's,  the 
introduction  of  a  magnet  into  the  axis  of  a  helix  of  insulated 
wire,  must  necessarily  induce  a  secondary  current  of  electricity, 
and  its  withdrawal  another  in  the  opposite  direction,  because 
the  magnet  corresponds  to  the  internal  helix  of  coarse  wire  car- 
rying the  primary  current,  Figs.  214,  216,  in  the  ca-eof  Volta- 
electric  induction,  §433.  The  direction  of  the  secondary  current 
actually  induced  by  the  magnet,  is  also  exactly  what  it  should 
be  if  Ampere's  theory  be  true.  Magneto-electric  induction  is 
then,  arter  all,  only  a  case  of  Volta-electric  induction. 

It  is  obvious  that  the  secondary  electricity  thus  induced  by 
the  magnet,  is  not  derived  from  the  magnet,  but  is  merely  the 
natural  electricity  of  the  wire  of  the  helix,  which  i>  momenta- 
rily disturbed  by  the  approach  and  withdrawal  of  the  magnet. 
The  effect  is  greater  the  longer  and  finer  the  wire,  and  the 
mare  numerous  the  convolutions  of  the  helix,  on  account  of 
thi  larger  amount  of  natural  electricity  which  can  be  oper- 
ated on  by  the  magnet,  and  on  account  of  the  inductive  action 
of  the  strands  of  the  helix  on  each  other,  as  already  de-cnbed 
in  the  case  of  Volta-electric  induction,  §439.  The  electricity 
thus  produced  is  possessed  of  greater  intensity  than  that  Wiiicii 
can  be  derived  from  any  battery,  however  powerful,  and  very 
closely  resembles  the  electricity  of  the  machine  in  regard  to 
giving  shocks  and  producing  light :  if  the  circuit  be  broken  at 
the  moment  when  the  magnetic  induction  takes  place,  spark;  of 
extraordinary  brilliancy  will  appear:  it  also  possesses  great 
power  of  effecting  chemical  decomposition,  and  may  often  be 
substituted  with  advantage,  both  for  the  common  electrical 
machine  and  the  galvanic  battery. 

459.  Volta-magneto-electric  Coils  for  inducing-  Secondary 
Electric  Currents.  Advantage  is  taken  of  these  principles  in 
the  construction  of  apparatus  for  the  production  of  steady  and 
apparently  continuous  currents  of  induced  electricity.  Thus, 

449,  How  does  Magneto-electric  induction  support  Ampere's  the  >ry?  What  is  the 
source  of  the  induced  electricity?  Why  is  the  effect  increased  by  lengthening  tao 
jire  and  multiplying  the  tiirus  of  the  helix? 


450 


PAGE  S 


in  Fig.  222,  if  the  primary  coil  be  arranged  in  such  a  way  that 
its  connection  with  the  battery  is  rapidly  completed  and  broken, 
by  a  mechanical  contrivance  adapted  to  the  purpose,  at  d,  then 
so  rapid  a  succession  of  secondary  currents  will  be  produced,  as 
to  have  the  effect  of  a  continuous  current,  causing  violent  oscil- 
lations of  the  galvanometer  needle,  vivid  sparks,  and  powerful 
shocks,  the  hands  being  previously  moistened  with  salt  water. 
The  violence  of  these  effects  may  be  regulated  by  the  number 
of  wires  introduced :  with  every  successive  wire,  all  the  effects 
above  described  are  proportionally  increased,  and  when  the  coil 
is  completely  filled,  the  torrent  of  sparks  becomes  insupportable. 
Sometimes  the  regulation  is  accomplished  by  placing  the  coils 
in  a  horizontal  position,  and  introducing  a  solid  iron  bar,  or  a 
bundle  of  wires,  a  shorter  or  longer  distance.  An  instrument 
of  this  construction  is  often  used  by  physicians  for  the  adminis- 
tration of  electricity  to  their  patients. 

451.  Pag-c's  Separable  Helices.  One  of  the  niost  perfect 
instruments  for  the  exhibition  and  application  of  a  secondary 
induced  current,  by  the  action  of  the  primary  current  of  the  bat- 
combined  with  an  electro-magnet,  has  been  invented  by 
our  countryman,  Dr.  Page,  and  is  represented  in  Fig.  226.  It 

consists  of  an  internal 
helix  of  coarse  wire, 
p,  of  three  strands, 
each  about  twenty- 
five  feet  long,  and 
hollow  in  the  axis, 
so  as  to  admit  of  the 
introduction  of  a  rod 
of  soft  iron,  or  of 
small  iron  wires.  On 
the  outside  of  the  in- 
ner helix  there  is  a 
second  helix,  s,  con- 
sisting of  from  one  to 
three  thousand  feet 

of   fine  wire.     It  is 

Page's  Separable  Helices,  witk  wires.  made  entirely  sepa- 

rate from  the  interior 

helix,  and  can  be  removed  from  it.     The  extremities  of  this 
helix  terminate  in  two  binding  cups  connected  with  the  wires, 


450.   How  can  F/'g-.  222  be  altered  so  as  to  produce  a  nearly  continuous  current  of 
electricity  ?    How  can  the  violence  of  its  action  be  regulated  ? 


SEPARABLE    HELICES.  451 

/>',  n.  The  extremities  of  the  inner  helix  are  connected  res, 
pectively  with  the  binding  cups,  +  and  — ,  through  the  iron 
rasp,  or  else  through  a  break-piece,  B,  attached  to  the  instrument. 
CXie  of  the  battery  wires  is  connected  with  the  binding  cup,  — , 
the  other  with  the  break-piece  B,  or  applied  to  tlu  iron  rasp. 
The  continual  making  and  breaking  the  circuit  in  the  inner 
coil,  induces  a  momentary  secondary  current  of  electricity  in 
the  outer  coil,  alternately  in  opposite  directions.  If  the  two  ends 
of  the  secondary  coil,  p  and  n ,  are  brought  near  each  other,  a 
bright  spark  flashes  at  every  break  in  the  primary  current,  even 
when  no  iron  wires  are  employed.  If  a  rod  of  soft  iron,  or  a 
bundle  of  wires,  w,  is  introduced  into  the  centre  of  the  helix, 
the  spark  is  very  much  increased,  brilliant  scintillations  are 
thrown  off,  and  the  shock  becomes  intolerable.  The  iron,  in 
acquiring  and  losing  magnetism  whenever  the  connection  with 
the  battery  is  made  and  broken,  induces  a  secondary  current 
in  both  the  coils,  which  is  shown  in  the  inner  coil,  in  the  in- 
creased scintillations  which  flash  from  the  rasp ;  and  in  the 
outer  coil,  by  the  violent  shocks  which  it  imparts.  Sometimes 
this  instrument  is  provided  with  a  mechanical  contrivance  moved 
by  clockwork,  for  breaking  the  primary  current,  and  in  this 
case,  none  of  the  power  being  consumed  in  producing  the  me- 
chanical motion  which  breaks  the  circuit,  a  very  small  battery 
will  answer  the  purpose.  If  a  silver  dollar  and  a  piece  of  zinc 
of  equal  size  be  used  simply  for  the  battery,  and  the  inner  helix 
be  filled  with  soft  iron  wires,  the  shock  is  quite  severe.  If  the 
extremities  of  the  secondary  coil  are  separated  at  the  same  in- 
stant that  the  bat-ery  current  is  broken,  a  spark  will  be  seen, 
and  a  bright  flash  produced,  provided  these  extremities  are 
tipped  with  charcoal  points,  and  held  almost  in  contact.  Water 
may  be  decomposed,  if  the  wires  are  made  of  platinum,  guarded 
by  glass,  and  dipped  into  the  liquid.  The  extremities  of  these 
wires  shine  in  the  dark,  one  constantly  bright,  the  other  inter- 
mi  ttingly.  Oxygen  and  hydrogen  are  given  off  in  small  quanti- 
ties at  each  wire,  and  rapid  discharges  are  heard  in  the  water. 
A  Leyden  jar,  the  knob  of  which  is  connected  with  the  inside 
ccating  by  a  continuous  wire,  may  be  feebly  charged,  and  slight 
shocks  rapidly  received,  by  bringing  the  knob  in  contact  with 
one  of  the  cups  of  the  outer  helix,  and  grasping  with  the  two 
hands  respectively  the  outer  coating  of  the  jar,  and  a  handle 
connected  with  the  other  cup.  If  a  bundle  of  soft  iron  wires,  w, 

451.   Describe  Page's  separable  helices.     How  is  the  break-piece  sometimes  arranged  ? 
Describe  the  eSfc3ts  produced  by  this  instrument.    How  may  a  Leydeu  jar  be  charged! 


452  THE    OPERATION    OF  ^ 

be  introduced  into  the  inner  coil  in  place  of  the  iron  rod,  the 
effects  described  above  are  much  increased.  The  sparks  and 
shocks  may  be  varied  at  pleasure  by  increasing  or  diminishing 
the  number  of  the  iron  wires,  the  addition  of  only  one  wire 
producing  a  decided  effect.  If  a  glass  tube  be  introduced 
around  the  iron  wires,  between  them  and  the  inner  coil,  their 
inductive  action  on  the  secondary  coil  is  not  d  minished,  but  if  a 
brass  tube  be  introduced  instead  of  the  glass,  their  inductive 
influence  upon  the  secondary  coil  will  be  destroyed,  so  far  as 
sparks  and  shocks  are  concerned :  if  the  tube  be  only  partially 
introduced,  their  inductive  effect  will  be  proportionably  reduced, 
but  not  entirely  destroyed:  the  distance  to  which  the  brass 
tube  is  introduced  constitutes  a  second  mode  of  regulating  the 
intensity  of  the  shocks.  The  brass  tube  neutralizes  the  induc- 
tive action  of  the  wires  by  destroying  the  secondary  induced 
current,  and  inducing  a  tertiary  current  in  both  the  coils,  flow- 
ing in  an  opposite  direction,  both  when  the  battery  current  is 
established  and  is  broken,  and  these  tertiary  currents  have  the 
effect  of  reducing,  if  not  destroying,  the  secondary  currents, 
which  would  otherwise  be  induced  in  the  coils :  this  is  always 
the  effect  of  any  closed  wire  circuit  in  the  immediate  neighbor- 
hood of  a  helix  or  coil  carrying  the  secondary  induced  current. 

As  the  two  coils  P  and  s,  are  separable,  it'  the  outer  coil  s 
be  removed,  and  the  inner  coil  be  so  arranged  as  to  constitute 
a  "part  of  the  battery  circuit,  which  is  broken  at  pleasure  by  the 
rasp  or  the  revolving  break-piece,  the  existence  of  the  extra 
current,  §438,  shown  by  the  increased  vividness  which  it  imparts 
to  sparks  and  shocks  when  the  battery  current  is  broken,  may 
be  very  satisfactorily  exhibited;  also  the  additional  effects  that, 
are  produced  by  inserting  a  soft  iron  rod  into  the  interior  of  the 
helix.  This  instrument  has  been  very  extensively  employed  by 
physicians  for  the  administration  of  electricity  to  their  patients, 
on  account  of  the  facility  with  which  the  strength  of  the  current 
can  be  regulated,  by  the  number  of  iron  wires  introduced,  by 
the  distance  to  which  a  brass  tube  enclosing  the  wires  is  pushed 
in,  or  by  the  distance  to  which  the  iron  wires  or  a  solid  red  is 
inserted :  for  greater  convenience,  it  is  usual  in  such  experi- 
ments to  mount  the  co.ls  in  a  horizontal  position. 

452.    The  Circuit-Breaker.     The  effect  of  this  instrument 
depends  to  a  great  degree  upon  the  suddenness  and  complete- 

What  is  the  effect  of  using  iron  wires  instead  of  an  iron  rod  ?  of  introducing  a  glass 
tube?  a  brass  tube?  Explain  the  latter  effect.  How  i^ay  the  existence  of  the  extra 
current  be  displayed  by  thin  instrument  ?  What  fc  the  arrangement  of  tn«  coils  when, 
physicians  ? 


THE    CIRCUIT-BREAKER.  453 

ness  with  which  the  primary  current  is  broken.  This  is  true  in 
all  cases  of  ihe  induction  of  secondary  currents  by  breaking  the 
primary  circuit.  It'  the  primary  current  be  not  broken  suddenly, 
b  it  g  adually,  there  is  a  proportionate  diminution  in  the  power 
of  the  secondary  current.  In  the  ordinary  modes  of  breaking 
the  circuit,  like  the  hammer  break-piece  of  Ruhmkorff's  coil, 
§4)3,  the  wires  being  slowly  separated,  there  is  an  opportu- 
nity for  th?  primary  current  to  pass  after  the  connection  is 
actually  sundered,  by  leaping  across  the  small  interval  which 
separates  them,  in  consequence  of  the  conducting  power  of  the 
air,  and  especially  for  the  extra  secondary  current  flowing  in  the 
primary  wire  to  do  so,  on  account  of  its  extreme  intensity, 
as  is  shown  by  the  vivid  spark  which  appears  under  these  cir- 
cuin >tances.  The  effect  of  this  spark  is  to  prolong  the  ex- 
istence of  fie  primary  and  extra  currents  in  the  inner  coil, 
and  consequently  prolong  the  existence  of  the  magnetism  in  the 
bundle  of  iron  wires,  and  prevent  them  from  being  de-inagnet- 
ized  as  quickly  as  they  otherwise  would  be.  This  tends  to 
prevent  that  suddenness  in  the  break  of  the  primary  current, 
and  de-ma ^netiza  ion  of  tli3  iron  on  which  the  intensity  of  the 
induced  current  depend',  and  greatly  reduces  its  power :  .the 
more  sudden  and  com,;lc;te  the  stoppage  of  the  primary  current 
and  the  annihilation  of  the  magnetism  of  the  iron  wires,  the 
more  vivid  and  intense  the  secondary  current  in  the  outer  coil, 
and  the  sparks  and  sha?ks  which  it  produces.  To  obviate  this 
difficulty,  and  to  promote  the  suddenness  and  completeness  of 
t!ie  break,  the  primary  coil  wire  f/om  one  pole  of  the  battery  is 
made  to  terminate  in  a  cup  filled  with  mercury,  whose  surface 
is  covered  with  a  thin  layer  of  spirits  of  turpentine  :  the  wire 
from  the  other  pole  of  the  battery  dips  into  the  mercury,  and  is 
so  arranged  that  when  raised  out  of  the  mercury  the  current  is 
broken,  when  depressed  the  current  is  established.  The  spirits 
of  turpentine  is  an  absolute  non-conductor  of  electricity,  and 
therefore  the  instant  the  wire  leaves  the  surface  of  the  mercury, 
its  extremity  being  drawn  up  into  a  non-conducting  medium 
instead  of  into  the  air,  the  flow  of  the  current  is  instantane- 
ou<ly  ami  completely  arrested,  no  spark  passes,  the  bundle  of 
i  on  wires  is  instantly  de-magnetized,  and  the  power  of  the 
secondary  current  and  the  various  effects  which  it  produces, 
very  greatly  increased:  water,  alcohol  and  naptha  are  some- 

452.  On  what  does  the  effect  of  this  instrument  greatly  depend?  Why  must  the 
breik  bo  sudden  and  complete?  Describe  and  explain  the  spark-arresting  circuit- 
breulier.  Explain  the  use  of  the  spirits  of  turpentine. 


454 


RUHMKORFF'S  COIL 


times  used  instead  of  spirits  of  turpentine.  This  contrivance, 
which  is  called  the  spaik-arresting  circuit-breaker,  was  the  in- 
vention of  our  countryman,  Dr.  Page,  in  1838,  and  is  one 
of  the  greatest  improvements  made  in  the  construction  of  coils 
for  the  production  of  induced  electricity  by  breaking  the  pri- 
mary current  >  one  of  similar  construction  was  introduced  in 
France  in  1856,  by  Foucault,  and  attached  to  Ruhmkorffs  coil. 
453.  Ruhmkorff's  Coil  for  inducing1  secondary  electrical 
currents.  One  of  the  most  interesting  and  extraordinary  of 
the  various  machines  for  producing  continuous  secondary  cur- 
rents of  electricity,  is  the  coil  of  RuhmkorfF,  a  philosophical 
instrument  maker  at  Paris,  of  which  a  section  is  given  in 
Fig.  227.  The  principle  of  this  instrument  is  precisely  the 

Fig.  227. 


Ruhmkorff '3  Coil  dissected. 

same  as  the  last  It  consists  of  two  concentric  coils  of  copper 
wire:  the  primary  or  inner  coil,  P,  p,  consisting  of  ten  or 
twelve  yards  of  copper  wire,  about  1-1 2th  of  an  inch  in  diame- 
ter, coiled  around  two  or  three  hundred  times :  and  the  outer 
or  secondary  coil,  s,  s,  made  of  very  long  and  thin  wire,  about 
1-1 00;  h  of  an  inch  in  diameter,  and  from  three  to  five  miles  in 
length,  the  coil  being  formed  by  20,000  to  25,000  turns  of  wire, 
and  terminating  in  the  wire*  t/*  and  e,  which  are  directly  con- 
nected with  tlvj  points  y  and  x.  The  inner  helix  is  coiled 
directly  on  a  cylinder  of  card-board,  forming  the  nucleus  of  the 
apparatus,  and  inclosed  in  an  insulating  cylinder  of  glass  or 
caoutchouc.  Great  attention  is  paid  to  the  insulation:  the 
wires  are  not  merely  insulated  by  being  wound  with  silk,  but 
each  individual  layer  is  insulated  from  the  others  by  a  coating  cf 

453.  Describe  Ruhmkorff's  Coil.     How  is  the  inner  coil  wound  ?  the  outer  coil?    How 
Is  insulation  secured  ? 


x  DISSECTED.  455 

shell-lac.  The  length  of  the  secondary  coil  varies  greatly ;  in 
some  of  the  larger  sizes  it  is  forty  or  fifty  miles,  and  made  of 
very  thin  wire :  the  thinner  the  wire  the  greater  the  tension  of 
the  secondary  current .  M,  is  a  cylindrical  bar  composed  of  soft 
iron  wires,  firmly  bound  together,  and  is  placed  in  the  axis  of  the 
instrument.  At  p  and  /i,  are  binding  screws,  for  establishing  a 
connection  between  the  primary  coil  and  a  battery  composed 
of  three  or  four  of  Grove's  cells.  The  battery  current  enters 
at  jo,  passes  on  by  the  metallic  band  to  the  pillar  c,  thence  to  d ; 
then  through  £,  to  the  primary  coil,  p,  p,  and  after  traversing 
the  whole  length  of  that  coil,  finally  rejoins  the  battery  through 
n ;  its  course  through  the  instrument  being  indicaied  by  the 
arrows.  The  circulation  of  the  battery  current  through  the 
primary  coil  admits  of  being  broken  at  c  and  d.  When  rf, 
which  is  a  small  hammer  suspended  from  a  pivot  at  #,  is  raised, 
the  current  is  broken ;  when  it  is  down,  the  current  is  contin- 
uous, parses  on  through  the  hammer,  and  after  traversing  the 
whole  of  the  primary  coil,  eventually  finds  its  way  back  to  the 
battery,  at  n.  As  soon,  however,  as  the  current  begins  to 
circulate  through  p,  p,  the  bundle  of  iron  wires,  M,  becomes 
strongly  magnetic,  attracts  d  from  the  pillar  c,  and  the  primary 
current  is  interrupted ;  the  instant  this  takes  place,  M  loses  its 
magnetism,  and  the  hammer,  d,  falls ;  as  soon  as  this  occurs, 
the  battery  current  immediately  begins  to  circulate  again,  and 
M  is  again  made  magnetic,  d  is  again  attracted,  the  current  is 
again  broken,  and  is  again  renewed.  The  break  in  the  current 
is  made  several  times  in  a  second,  and  by  mechanical  means 
may  be  made  much  more  rapid.  By  each  of  these  interrup- 
tions, a  powerful  secondary  current  is  momentarily  induced  in 
the  outer  coil  of  fine  wire,  s,  s,  partly  by  the  inductive  influ- 
ence of  the  primary  current  itself,  and  partly  by  the  influence 
of  the  magnetism  momentarily  induced  and  destroyed  in  the 
bar  M,  according  to  the  principles  stated  in  the  preceding  sec- 
tions :  if  there  be  a  break  in  the  secondary  coil,  as  at  y  and  x, 
Fig.  227,  the  electricity  will  leap  across  the  interval  with  the 
production  of  vivid  sparks.  Every  time  the  connection  with  the 
battery  is  broken,  two  direct  secondary  currents,  one  of  positive 
and  the  other  of  negative  electricity,  are  induced,  moving  in  the 
same  direction  with  the  battery  current.  Two  inverse  secon- 
dary currents  of  positive  and  negative  electricity,  moving  in  the 
opposite  direction  from  the  battery  current,  are  also  induced  at 

Describe  the  arrangement  of  the  coils.     How  is  the  current  broken  ?    IIow  many  cur- 
rents are  induced  at  every  break  and  completion  of  the  circuit  ? 


456  THE    EFFECT    OF 

every  completion  of  the  battery  current:  consequently  each  of 
the  po.es  y  and  or,  is  alternately  affected  with  positive  and  neg- 
ative electricity,  and  if  equal  in  quantity  and  tension,  would 
exactly  neutralize  each  other.  But  the  currents  induced  when 
the  current  is  completed,  are  not  equal  to  those  induced  when 
the  connection  is  broken :  on  breaking,  the  current  is  of  shorter 
duration  and  more  tension;  on  completion,  of  longer  duration 
and  less  tension.  When  the  two  extremities  of  the  outer 
coil,  y  and  x,  are  connected  by- a  continuous  wire,  the  direct 
and  inverse  currents  being  nearly  equal  in  aggregate  power, 
the  latter  partially  neutralize  the  former;  but  if  the  two 
extremities  of  the  coil  are  separated  at  y  and  x,  as  in  Fig.  227, 
the  resistance  of  the  air  is  then  opposed  to  the  passage  of 
the  currents,  and  only  the  current  which  has  the  superior  ten- 
sion, i.  e.,  the  direct  current  produced  by  breaking  connection, 
and  moving  in  the  same  direction  with  that  of  the  battery,  is 
able  to  leap  over  the  interval  and  effect  a  passage :  the  sepa- 
ration of  the  two  currents  is  more  complete  the  greater  the 
interval,  up  to  a  certain  point,  when'  neither  pass,  and  there  is 
then  nothing  induced  at  the  poles  y  and  x,  but  electrical  tensions 
alternately  in  contrary  directions.  Consequently,  in  Fig.  227, 
as  it  is  the  direct  current  corresponding  with  the  battery  cur- 
rent only  that  passes  between  #  and  x,  y  must  be  taken  as  the 
positive  pole,  and  x  as  the  negative  pole,  because  they  discharge 
intermittent  streams,  the  one  of  positive  and  the  other  of  neg- 
ative electricity  exclusively.  These  currents  are  of  extreme 
intensity,  and  produce  vivid  sparks  which  succeed  each  other 
in  continuous  succession.  The  intensity  of  these  sparks  may  be 
greatly  increased  by  increasing  the  suddenness  with  which  the 
continuity  of  the  primary  current  is  broken. 

453.*  The  Condenser.  Its  effects  explained.  The  power  of 
the  instrument  may  also  be  greatly  increased  by  attaching  to  the 
primary  co  1  a  modification  of  the  Ley  den  jar,  called  a  Condenser. 
This  consists  of  150  sheets  of  tinfoil  about  18  inches  square, 
exposing  a  total  surface  of  about  75  square  yards.  These 
sheets  are  pasted  together  so  as  to  form  two  large  sheets,  and 
then  attached  to  the  two  sides  of  a  sheet  of  oiled  silk,  which 
completely  insulates  them,  thus  forming  in  effect  a  very  large 
]>yden  jar.  They  are  then  coiled  several  times  around  each 
other,  so  that  the  whole  can  be  packed  beneath  the  base  of  the 
instrument.  One  of  these  sheets,  the  positive,  is  connected 
with  the  binding  cup  ri,  Fig.  227,  so  as  to  communicate  with 

Explain  why  the  direct  currents  alone  can  force  a  passage.     How  may  the  vividness 
of  the  sparks  be  increased  ?     What  is  the  arrangement  of  the  condenser  ?     What  ellect 


THE    CON'OEXSER.  457 

the  primary  current  when  it  passes  into  the  primary  coil ; 
the  other,  the  negative,  is  connected  with  the  binding  screw  p 
whk'h  communicates  directly  with  the  battery  current :  these 
correspond  with  the  binding  screws  G  and  H,  in  Fig.  228.  The 
operation  of  this  instrument  seems  to  be  as  follows. — We  have 
seen,  §439,  that,  at  each  break  of  the  battery  current,  an  induced 
extra-current  in  the  same  direction  is  produced  in  the  pri- 
mary coil  itself;  and  it  is  this  which  produces  the  spark  that 
passes  at  each  moment  between  the  hammer  and  the  anvil: 
being  in  the  same  direction,  and  prolonging  the  existence  of  the 
direct  current  in  the  primary  coil,  it  tends  to  prolong  also  the 
magnetic  effect,  and  to  prevent  the  bundle  of  soft  iron  wires 
from  being  de-magnetized  as  quickly  as  it  would  be  otherwise. 
By  attaching  the  condenser  to  the  primary  current,  the  extra 
current,  instead  of  producing  a  strong  spark,  darts  into  the  con- 
denser, the  positive  electricity  into  one  sheet,  and  the  negative 
into  the  other :  they  then  combine  quickly  by  the  primary  coil, 
by  the  baflery,  and  the  circuit,  H,  L,  Fig.  '228,  and  in  so  doing 
give  rise  to  a  current  in  a  direction  opposite  to  that  of  the  prima- 
ry current,  wlrch  instantly  de-magnetizes  the  bundle  of  toft  iron 
wires,  and  renders  the  break  of  the  primary  current  much  more 
sudd  an  and  complete.  Tue  peculiar  action  of  the  condenser 
u  )on  the  coil  by  the  absorption  of  the  extra  current,  was  discov- 
ered by  Fizeau  at  Paris  in  1853  :  by  connecting  the  plates  of 
the  coaden^er  with  each  side  of  the  circuit-breaker,  he  found  that 
the  sparks  discharged  at  the  hammer  by  the  extra-current 
were  diminished,  while  those  of  the  outer  coil  at  y  and  #,  were 
dojble  1  in  length.  It  was  soon  attached  to  the  coil  by  Ruhm- 
koivf,  and  the  intensity  of  the  secondary  current  so  exalted  as 
to  lengthen  its  spark  fro'ii  one-eighth  to  a  little  more  than  half 
an  inch.  This  was  the  first  great  improvement  made  upon  the 
coil  as  constructed  by  Dr.  Page.  Other  improvements  were 
added  in  1856  and  1857,  by  means  of  which  the  power  of  the  in- 
strument wa>  gradually  increased,  until  finally  sparks  of  extreme 
intensity,  from  eighteen  to  twenty  inches  in  length,  were  obtain- 
ed iron  the  secondary  coil  at  y  and  x.  The  rapid  de-inagnet- 
iz  ition  is  also  greatly  accelerated  by  making  usa  of  a  bun-J  •* 
of  iro  i  wire?  instead  of  a  solid  bar  of  soft  iron.  This  improve 
meat  was  made  by  Dr.  Page  in  1838,  in  the  construction  of  hi.-, 
scparab'e  helices,  §451 :  this  effect  seems  to  be  produced  in  great 
part  by  the  neutralizing  influence  of  the  similar  poles  of  the 

lists  it  upon  the  extra  current  spark  ?  Upon  the  spark  of  the  secondary  coil  1  Explain 
it  operation.  Who  discovered  this  fact  I  What  effect  is  produced  upon  the  suddenness 
of  de  magnetization  by  the  use  of  iron  wires  1 


458 


RUHMKORFF'S  COIL  COMPLETE. 


wires  on  each  other.  Thus  it  appears  that  by  the  coils  of  Page 
and  Ruhmkorff,  galvanic  electricity  of  low  tension  may  be  u-ed 
to  induce  statical  electricity  as  intense  as  that  of  the  ordinary 
electrical  machine,  while  its  quantity  is  far  greater;  so  th:it 
they  may  be  substituted  with  great  advantage  for  that  machine 
in  most  cases,  where  a  continuous  discharge  of  sparks  and 
shocks  is  required. 

454.    Ruhmkorff's  Coil  complete.     The  same  instrument  is 
represented  in  relief,  in  Fig.  228  :  K,  represents  a  milled  handle 

Fig.  228. 


Coil  complete. 


by  which  the  cylinder  L,  called  the  Commutator,  consisting  of 
alternate  pieces  of  copper  and  ivory,  is  turned  so  as  to  bring 
either  piece  into  contact  with  the  metallic  spring  o  and  re- 
verse the  direction  of  the  primary  current  through  the  coil, 
by  connecting  at  pleasure  with  the  positive  or  negative  pole 
of  the  battery  :  A,  is  the  binding  screw  through  which  the  posi- 
tive current  from  the  battery  enters,  and  there  is  another  on  the 
opposite  side  of  L,  not  seen  in  the  Fig.,  for  the  passage  of  the 
negative  current  :  from  A,  the  positive  current  passes  up  the 
spring  o,  into  the  commutator  L,  by  which  it  is  transmitted  to 
the  commencement  of  the  primary  coil,  making  its  exit  at  I  : 
it  then  proceeds  to  the  hammer  D,  through  N,  to  the  binding 
cup  H,  whence  it  returns  to  the  negative  pole  of  the  battery: 
M,  is  the  bundle  of  soft  iron  wires,  occupying  the  core  of  the 
instrument:  Y  and  x,  are  the  binding  screws  connected  with 
the  extremities  of  liie  outer  or  secondary  coil,  and  which  may 

Inscribe  KuhmkorlT's  Co:',  as  represented  in  Fig.  228. 


RITCHIE'S  459 

be  brought  into  connection  with  each  other  by  wires,  as  at 
y  and  a:,  in  Fig  227  :  the  condenser  is  attached  at  G  and  II. 
On  turning  the  handle  K,  so  as  to  bring  the  metallic  piece  L 
into  contact  with  the  spring  o.  the  primary  current  immediately 
circulates  through  the  inner  coil,  and  a  shower  of  vivid  sparks 
flashes  continually  from  x  to  T,  when  the  proper  connections 
are  made  by  wires  nearly  touching  each  other.  With  largo 
coils  the  hammer  cannot  be  used,  on  account  of  the  extreme 
violence  of  the  spark  produced  by  the  extra-current;  tin 
surfaces  become  so  much  headed  as  to  melt :  to  obviate  this 
difficulty,  and  to  promote  the  suddenness  and  completeness  of 
the  break  in  the  circuit,  a  mercury  circuit -breaker,  §452,  has 
been  invented,  by  which  the  power  of  the  instrument  has  been 
greatly  increased  and  the  use  of  the  hammer  discontinued :  more 
recently,  mechanical  means  have  been  employed  for  breaking 
the  circuit  slowly  or  rapidly,  at  the  pleasure  of  the  operator  :  by 
these  and  other  improvement-,  this  very  interesting  and  re- 
markable instrument  has  been  brought  from  a  comparatively 
feeble  state  to  a  very  high  degree  of  efficiency,  by  our  country- 
man, Mr.  Ritchie,  a  philosophical  instrument  maker  at  Boston. 

455.  Ritchie's  improved  RuhmkorT  Coil.  The  length  of 
the  secondary  spark  which  Ruhmkorff  obtained  i:i  his  original 
coil,  did  not  equal  one  inch:  in  1857,  Hoarder,  in  England,  by 
more  carefully  insulating  the  coils,  obtained  sparks  of  three 
inches :  it  was  found  impossible  to  make  larger  and  more  pow- 
erful coils,  in  consequence  of  a  discharge  taking  place  within 
the  coils,  the  current  forcing  a  passage  from  strand  to  strand 
between  the  outer  and  inner  portions  and  breaking  down  the 
insulation,  the  successive  layers  of  wire  being  only  separated 
by  insulating  media ;  and  the  longer  and  finer  the  outer  coil, 
the  stronger  is  the  tendency  for  the  secondary  current  to  force  a 
passage  laterally  through  the  adjoining  layers  in  preference 
to  passing  through  the  immense  length  of  the  secondary  wire, 
amounting  in  some  cases  to  eighty  miles.  In  1857,  Mr.  Ritclve 
devised  a  mode  of  winding  the  wire  of  the  outer  helix  in  sev- 
eral different  sections,  carefully  insulated  from  each  other :  the 
first  section  commences  near  the  axis  just  upon  the  outside 
of  the  primary  coil,  and  gradually  extends  to  the  outer  circum- 
ference, in  a  plane  perpendicular  to  the  axis,  (in  the  m :um"i* 
that  sailors  coil  ropes  on  the  deck)  ;  then  continues  to  the  next 
section,  which  is  carefully  insulated  from  the  first,  and  wound 
from  the  outer  circumference  to  the  inner,  and  so  on  altern- 

Describe  Ritchie's  improved  Ruhmkorff  Coil. 


460 


IMPROVED 


a'e'y  from  sec 'ion  to  section,  until  the  coil  is  completed:  in 
this  manner,  in  consequence  of  the  division  of  the  outer  coil 
in:o  many  section.?,  and  their  very  perfect  insulation,  it  be- 
comes impossible  for  the  secondary  current  to  force  a  lateral 
pa  ?age  and  break  through  the  coil.  The  result  was,  that, 
in  1837,  coils  were  ma  le  which  gave  sparks  of  twelve  and  event- 
ually sixteen  inches,  in  place  of  three.  The  instrument  con- 
sists of  a  primary  coil  of  copper  wire  about  1-Gth  of  an  inch 
in  d'ameter  and  about  150  feet  in  length,  wound  in  three 
courses,  very  carefully  annealed,  and  mounted  vertically,"  as  in 
Fig.  229  :  thio  coil  is  completely  covered  externally  with  gutta- 

Fig.  229. 


Ritchie's  Improved  Ruhmkorff  Coil. 

pcrchi  ^Olhsof  an  inch  in  thickness,  and  passing  entirely 
through  the  basement  to  a  plate  of  the  same  substance,  to 
will-  h  it  is  united:  within  this  coil  is  placed  the  bundle  of  soft 
iron  wires :  over  the  primary  coil  and  magnet  a  thick  glass  cyl- 
inder or  bell  is  placed,  closed  at  the  top,  and  provided  with  a 
knob  by  which  it 'can  be  raised  from  its  position.  On  the  out- 


RUHMKORFF    COIL.  4^1 

side  of  this  glass  bell  is  placed  the  secondary  coil,  consisting 
of  very  fine  copper  wire,  about  1-1 00th  of  an  inch  in  diameter, 
very  carefully  insulated  by  silk  winding,  from  three  to  thirty, 
and  even  eighty  miles  in  length,  wound  in  the  manner  above 
described,  upon  a  cylinder  of  gutta-percha :  the  extremities  of 
this  coil  are  enclosed  in  rubber  tubes  and  carried  to  insulated 
glass  pillars,  from  which  the  induced  current  is  taken  by  plati- 
num wires  in  whatever  direction  it  may  be  required  :  in  Fig.  229, 
it  is  conveyed  to  the  electric  Egg,  for  the  purpose  of  exhibiting  its 
extraordinary  illuminating  power  when  discharged  through  a 
vacuum.  The  condenser  is  made  of  tin-foil  pasted  on  tissue 
paper,  of  three  thicknesses  between  each  stratum  :  it  is  composed 
of  three  sections,  of  50,  100,  and  150  feet,  which  by  means  of 
screws  can  be  used  separately  or  in  combination  ;  this  is  packed 
beneath  the  basement  and  directly  connected  with  the  binding 
screws  of  the  circuit-breaker.  The  interrupter,  or  circuit- 
breaker,  is  raised  by  means  of  a  small  crank  worked  by  hand, 
operating  upon  a  ratchet  wheel,  whose  teeth  strike  the  extremity 
of  a  delicately  adjusted  lever,  from  the  other  end  of  which  the 
hammer  is  suspended :  the  rapidity  of  the  break  in  the  circuit 
may  be  varied  at  pleasure  by  turning  the  crank  slowly  or  rap- 
idly :  the  battery  current  is  derived  from  two  to  four  cells  of  Bun- 
sen's  carbon  battery.  When  the  crank  is  turned  very  slowly, 
the  connection  of  the  primary  coil  with  the  battery  is  prolonged, 
and  the  bundle  of  iron  wires  becomes  very  highly  magnetized  : 
the  break  thenoccurs  very  suddenly,  and  instantaneously  develops 
the  entire  force  of  the  secondary  current,  producing  sparks  of 

freat  length  and  density,  the  discharge  being  surrounded  by  a 
ind  of  burr :  if  the  velocity  of  the  rotation  be  gradually  in- 
creased, the  spark  assumes  the  luminous  appearance  of  the 
sparks  of  the  electrical  machine  :  if  the  velocity  be  still  further 
increased,  the  luminous  discharge  will  disappear,  for  there  will 
not  then  be  sufficient  time,  between  the  establishment  and  break 
of  the  connection  with  the  battery,  to  magnetize  the  iron  core 
on  which  the  intensity  of  the  induced  secondary  current  chiefly 
depends.  The  power  of  this  instrument  is  vastly  greater  than 
that  of  any  electrical  machine  ;  sparks  of  more  than  twelve 
inches  in  length  can  easily  be  obtained,  discharges  can  be  made 
so  rapidly  as  to  appear  continuous,  and  a  Leyden  jar  can  be 
charged  and  discharged  with  so  much  rapidity  as  to  exhibit 
hardly  any  perceptible  interval,  and  with  a  noise  almost  stunning. 

-How  is  the  circuit-breaker  of  Ritchie's  machine  arranged  ?    What  is  the  effect  upou 
the  power  of  the  instrument  ? 


462  THE    CHARGING   OP 

This  machine  of  Ritchie's  excited  much  attention  in  Europe. 
It  wa>  exhibited  by  Gassiot,  before  the  Koyal  Society,  London, 
in  18-)8,  arid  by  McCullough,  at  Paris,  in  Ic'sGO.  Its  mode  of 
winding  was  almost  immediately  adopted  by  Ruhmkorff,  and 
the  secondary  coil  still  further  lengthened,  amounting  in  some 
cases  to  100,000  French  metres,  or  even  more, — from  sixty  to 
eighty  miles,^and  projecting  sparks  two  feet  in  length :  this 
took  place  in  1860;  and  in  1864,  he  received  as  a  reward  the 
prize  of  50,000  francs  offered  by  the  French  Emperor  in  1852, 
for  the  most  important  discovery  connected  with  the  develop- 
ment of  electricity. 

456.  The  management  of  Ruhmkor T's  Coil.  The  charg- 
ing- of  a  Leyden  jar.  The  principal  steps  in  the  improvement 
of  induction  coils,  as  first  constructed,  are  the  increased  length 
and  fineness  of  the  secondary  coil,  the  employment  of  soft  iron 
wires  instead  of  the  iron  bar  in  the  inner  coil,  and  the  spark- 
arresting  circuit-breaker, — all  inventions  of  Dr.  Page :  the 
discovery  of  the  effect  of  the  condenser  by  Fizeau,  and  its 
application  by  Ruhmkorff;  and  the  peculiar  mode  of  winding, 
combined  with  very  perfect  insulation,  devised  by  Ritchie  : — to 
the  combined  effect  of  these  various  improvements,  made 
through  a  series  of  many  years,  the  extraordinary  power  of 
Ruhmkorff's  coil,  in  its  most  perfect  form,  is  due.  Several 
coils  may  be  combined  so  as  to  increase  the  quantity  of  elec- 
tricity which  they  will  furnish,  by  placing  them  side  by  side 
and  connecting  them  by  wires  in  such  a  manner  that  the  bat- 
tery current  will  circulate  through  the  primary  helix  of  each 
coil  in  succession,  thereby  forming  in  effect  one  long  pri- 
mary coil:  as  only  one  hammer  is  required  for  the  purpose 
of  breaking  the  current,  the  remain'ng  hammers  should  be 
removed :  in  like  manner  the  secondary  coils  should  all  be 
connected  by  wires,  so  as  to  unite  all  the  positive  poles  together 
into  one  pole,  arid  all  the  negative  poles  into  the  other :  the 
extreme  positive  and  negative  poles  may  then  be  brought 
together  for  the  purpose  of  displaying  the  effects  of  the  instru- 
ment in  the  usual  manner :  by  this  arrangement  the  quantity 
of  electricity  will  be  greatly  increased,  but  no  increase  in  the 
tension  of  the  current  will  be  obtained.  If  an  increase  of  ten- 
sion is  required,  each  secondary  circuit  must  be  connected  in 
a  regular  series,  the  positive  pole  of  one  to  the  negative  pole  of 

What  improvement  was  made  by  Ruhmkorff?  with  what  result? — 456.  State  the  suc- 
cessive improvements.  How  may  coils  be  combined  so  as  to  increase  the  quantity  of 
the  current  ?  the  tension  ? 


^  A    LEYDEN   JAR. 

the  next,  so  as  to  form  in  effect  but  one  secondary  coil,  each  pri- 
mary coil  being  excited  by  a  separate  battery.  A  Leyden  jar 
may  be  charged  by  connecting  the  outer  coating,  Fig.  230,  with 

Fig.  230. 


Tlie  charging  of  a  Leyden  jar  by  Ruhmkorff^s  Coil. 

one  of  the  poles  of  the  coil,  and  the  inner  with  one  of  the  arms  of 
a  discharger,  the  other  arm  of  which  is  in  communication  with 
the  opposite  pole  of  the  coil :  the  extremities  of  the  discharger 
should  be  placed  two  or  three  inches  apart :  after  a  few  sparks 
have  passed,  the  jar  may  be  removed  and  discharged  in  the 
usual  manner :  with  a  large  instrument  an  electrical  battery 
containing  several  jars,  and  exposing  ten  square  feet  of  surface, 
may  be  charged  to  saturation  in  a  few  seconds,  and  far  more 
rapidly  than  by  an  ordinary  electrical  machine.  If  instead  of 
the  above  arrangement,  the  outer  coating  of  the  jar  be  connected 
with  one  pole  of  the  coil,  and  the  inner  with  the  other,  the 
poles  of  the  coil  being  at  the  same  time  connected  by  wires  set 
about  one  inch  apart,  the  Leyden  jar  will  be  constantly  charged 
and  discharged  without  cessation,  the  discharge  taking  place  as 
a  spark  two  or  three  inches  in  length,  very  bright,  and  produc- 
ing a'n  explosive  sound,  which  seems  to  be  continuous.  If  a 
platinum  wire  be  twisted  around  the  knob  of  a  Leyden  jar, 
and  its  ends  be  brought  near  enough  to  the  poles  of  the  secon- 
dary coil  to  almost  touch  them  without  quite  doing  so,  a  noise- 

IIow  can  a  Leyden  jar  be  charged  ?     What  experiment  may  be  tried  with  the  coil  ami 
Leaden  jar  ?     VVhat  Is  the  effect  of  charging  large  electrical  batteries  by  cascade  ? 


464  THE    EFFECTS    OF   RUHMKORFF'S    COIL.  -"i 

less  spark  of  feeble  light  will  pass  from  each  pole  to  the  end  of 
the  platinum  wire  nearest  it,  at  both  interruptions  ;  if  now  the 
outer  coating  of  the  jar  be  connected  with  one  of  the  secondary 
poles,  the  spark,  at  the  interruption  on  that  side,  will  suddenly 
become  brilliant  and  noisy  :  the  noiseless  spark  will  kindle  paper 
or  other  combustible  objects,  while  the  noisy  flash  from  the 
Leyden  jar  will  fail  to  kindle  them.  With  Ruhmkorff's  large 
coil,  electrical  batteries  may  be  charged  and  discharged  with  a 
continuous  and  almost  deafening  noise.  The  most  brilliant  ef- 
fects are  produced  by  charging  a  series  of  jars  by  cascade. 
When  six  jars,  each  containing  about  two  square  feet  of  coat<  d 
glass,  are  employed,  a  continuous  stream  of  dazzling  light  six 
inches  in  length,  is  produced,  accompanied  by  a  noise  that 
speedily  becomes  almost  intolerable.  With  one  jar,  the  dis- 
charge spark  is  two  and  one-half  inches  long ;  with  two  jars, 
three  and  a  half  inches ;  with  three  jars,  four  and  one-quarter 
inches ;  with  four  jars,  five  inches  ;  and  with  five  jars,  five  and 
a  half  inches. 

457.  The  Mechanical  effects  of  Ruhmkorff's  Coil.     The 
effects  of  Ruhmkorff's  coil  are  vastly  more  intense  than  those 
of  the  battery,  and  may  be  classed  under  the  heads,  Mechani- 
cal,   Physiological,  Heating,    Luminous,  and   Chemical.     The 
mechanical  effects  of  the  secondary  current  produced  by  this 
coil  are  disruptive  in  their  character,  and  resemble  those  of  a 
flash  of  lightning.     For  this  reason  it  should  be  passed  through 
glass  vessels  with  the  greatest  caution.     With  the  largest  appa- 
ratus, glass  plates  two  inches  thick  have  been  perforated.     It 
should  not    be  used  for  firing  Eudiometers,  except  with  the 
greatest  care  and  the  employment  of  a  very  small  battery. 

458.  The  Physiological  Effects.     The  physiological  effects 
are  extremely   intense.      The   shocks   are   so   powerful,   that 
oftentimes    careless    experimenters  have   been   prostrated   by 
them.     With  two  of  Bunsen's   cells  attached  to  the  primary 
coil,  hares  and  rabbits  have  been  killed,  arid  a  somewhat  lar- 
ger number  would  be  sufficient  to  kill  a  man. 

459.  The  Heating-  Effects.    The  heating  effects  are  intense. 
If  a  thin  iron  wire  be  stretched  between  the  two  points  y  and  x, 
it  is  immediately  melted   and  burned  with  a  vivid  light:  if 
each  of  the  poles  y  and  x,  be  terminated  with  a  fine  iron  wire, 
whose  extremities  are  brought  near  enough  together  almost  to 
touch,  Fig.  231,  the  wire  connected  with  the  negative  po-e  will 
melt  into  a  little  globule  of  liquid  iron,  while  the  other  will 

457.  What  are  the  Mechanical  effects  of  the  coil? — 458.  What  are  the  Physiological 
effects  ?— 459.  What  are  the  Heating  effects  ?    Is  there  any  difference  in  the  temperature 


THE    HEATING    EFFECTS. 


465 


T/ie  heating  effects  of  the  poles  of  Ruhmkorff's  Coil. 


Fig.  232. 


231<  remain  cold  enough  to 

be  held  in  the  fingers, 
Fig.  232,  and  if  a  re- 
flection of  these  points 
be  thrown  upon  a 
screen  by  means  of 
Duboscq's  electric 
lamp,  Fig.  1 60,  a  cone 
of  vapor  will  appear 
to  issue  from  the  point 
of  each  wire,  but  that  from  the  negative  wire  being  the  most 

powerful,  apparently  beats 
back  the  heated  stream  from 
the  positive  wire.  These  ef- 
fects are  the  reverse  of  those 
produced  in  the  voltaic  arc 
of  the  galvanic  battery,  in 
which  the  greatest  dispersion 
of  matter  and  the  highest 
temperature,  are  observed  to 
occur  at  the  positive  pole. 
The  heat  is  sufficiently  in- 
tense to  inflame  all  combust- 
ible substances,  and  to  fuse 
and  burn  metals.  Great 
use  is  made  of  this  in  Spec- 
trum analysis,  §285,  6,  7.  Another  very  remarkable  effect  of 
Ruhmkorif  's  coil,  first  noticed  by  Dr.  Page,  is  the  ignition  of 
disintegrated  conductors :  shreds  of  metal  and  other  conducting 
substances  in  a  pulverulent  condition,  are  ignited  and  fused : 
a  very  small  machine  will  ignite  a  pencil  mark  of  plumbago, 
even  through  many  miles  of  wire,  and  shreds  of  iron  over 
an  inch  in  length.  Advantage  has  been  taken  of  this  in  the 
construction  of  fuses  for  firing  gunpowder  in  blasting,  and  in 
the  discharge  of  fire-arms.  A  fuse  has  been  invented  called 
from  its  inventor,  Statham's  fuse,  which  depends  upon  the  ig- 
niting action  of  the  current  upon  the  sulphide  of  copper.  It 
has  been  found  that  in  a  copper  wire  covered  with  vulcanized 
gutta-percha  or  india-rubber,  a  layer  of  sulphide  of  copper  forms, 
after  some  months,  at  the  point  of  contact  of  the  metal  and  its 
coating,  which  is  sufficient  to  conduct  the  current.  If  a  por- 

of  the  poles  ?  Which  is  the  hotter  ?  How  do  the  poles  appear,  when  seen  by  Dnhoscq's 
lamp  ?  How  do  these  effects  compare  with  those  of  the  battery  ?  What  is  the  degree 
of  the  heat  ?  What  effect  is  produced  upon  shreds  of  metal  ? 


One  pole  cold. 


466  STATIIAM'S  FUSE. 

tion  of  the  coating  be  removed  from  a  wire  loop,  Fig.  233,  and 

Fig.  233. 


Statham^s  Fuse. 

a  quarter  of  an  inch  of  the  wire  cut  away,  the  current,  inter- 
rupted at  a  and  b,  finds  a  passage  by  means  of  the  sulphide  of 
copper,  which  it  ignites,  and  any  inflammable  substance  like 
gunpowder  or  gun-cotton,  placed  in  this  cavity,  takes  fire.  A 
very  powerful  battery  would  be  required  to  ignite  such  a  fuse, 
but  with  RuhmkorfPs  coil,  only  one  or  two  of  Bunsen's  ele- 
ments are  required,  the  ends  of  the  secondary  helix  being 
connected  with  A  and  B.  This  fuse  has  been  very  successfully 
employed  in  exploding  mines  in  the  works  at  Cherbourg,  in 
France:  six  mines  were  simultaneously  fired  at"  a  distance 
of  1,500  feet  from  the  apparatus.  Recently  a  more  sensitive 
priming  material  has  been  introduced,  consisting  of  ten  parts  of 
sub-phosphide  and  forty -five  of  sub-sulphide  of  copper,  and  fif- 
teen of  chlorate  of  potash,  finely  powdered  in  a  mortar,  with  the 
addition  of  sufficient  alcohol  to  moisten  it  throughout :  the  mix- 
ture is  dried  and  preserved  until  required,  in  close  vessels.  The 
magneto-electric  machine  to  be  presently  described,  §467,  is  now 
generally  employed  for  firing  such  fuses,  and  it  is  stated  that  one 
such  machine  contained  in  a  box  of  a  cubic  foot  in  size,  worked 
by  hand,  in  a  telegraph  office  in  Washington,  has  exploded  a 
cartridge  of  powder  in  an  office  in  New  York,  over  200  miles 
distant.  Another  very  common  application  of  Ruhmkorff's 
coil,  is  to  the  simultaneous  lighting  of  theatres  and  large  halls, 
by  the  discharge  of  the  current  through  platinum  points  placed 
in  the  gas-jets. 

460.  The  Luminous  Effects.  The  Luminous  effects  of 
Ruhmkorff's  coil  are  also  very  extraordinary,  and  vary  as  they 
take  place  in  air,  in  vacuo,  or  in  very  rarefied  vapors.  In  the 
air,  a  very  bright  and  loud  spark  is  produced,  which,  with  the 
coils  of  the  largest  size,  has  a  length  of  eighteen  or  twenty 

Describe  Statham's  fuse.    What  applications  are  made  of  these  fuses  ?— 460.  Describe 
the  Luminous  effects  of  Ruhmkorff  'a  coil  in  air :  in  vacuo. 


THE    LUMINOUS 


467 


'inches.  If  the  discharge  be  made  to  take  place  in  vacuo,  in  an 
exhausted  receiver,  an  extremely  beautiful  auroral  light  is  pro- 
duced, extending  through  an  interval  of  one  or  two  yards.  The 
experiment  is  made  by  connecting  the  two  wires  of  the  secon- 
dary coil  with  the  extremities  of  the  electrical  egg,  Fig.  229. 
This  is  screwed  upon  the  plate  of  an  air  pump,  and  a  vacuum, 
as  complete  as  possible,  produced.  As  soon  as  the  sparks  are 
allowed  to  pass,  a  beautiful  luminous  trail  is  observed  to  flow 
from  one  knob  to  the  other,  Fig.  234,  No.  1,  the  negative  ball 


The  Luminous  effects  of  Ruhmkorff'^s  Coil. 

is  surrounded  by  a  quiet  glow  of  light,  whilst  a  pear-shaped 
luminous  discharge  takes  place  from  the  positive  ball;  between 
the  two  is  a  small  interval,  nearer  to  the  negative  than  the  pos- 

How  is  the  experiment  performed?    Describe  No  1,  in  Fig.  234. 


468 


EFFECTS    IN    VACUO 


itive  ball  which  is  not  luminous.  The  discharge  is  constant, 
and  as  bright  as  that  obtained  from  a  powerful  electrical  ma- 
chine. When  the  exhaustion  of  the  receiver  is  very  perfect, 
the  luminous  portion  is  traversed  by  a  series  of  dark  bands  or 
arches  concentric  with  the  positive  ball,  Fig.  234,  No.  2 : 
the  presence  of  a  little  vapor  of  phosphorus  renders  these  dark 
bands  much  more  distinct.  If  the  finger  be  applied  at  the  side 
of  the  egg,  the  connection  of  the  lower  knob  with  the  negative 
pole  of  the  coil  being  broken,  the  trail  suffers  a  curious  devia- 
tion, and  is  drawn  towards  the  finger,  Fig.  234,  No.  3.  The 
positive  pole  possesses  the  most  brilliancy,  and  its  light  is  red, 
like  fire,  while  that  of  the  negative  pole  is  feeble,  and  of  a 
violet  color.  If,  instead  of  using  an  electric  egg,  the  receiver 
of  an  air  pump  be  employed,  containing  a  tumbler  made  of 
Uranium  glass,  lined  with  tin-foil  about  half-way  up  the  in  ide, 
and  a  metallic  rod  be  passed,  air-tight,  through  the  top  of  the 
jar,  until  it  touches  the  metallic  lining  on  the  inside  of  the 
tumbler ;  then,  on  connecting  one  pole  of  the  coil  with  the  plate 
of  the  air-pump,  Fig-  235,  and  the  other  with  the  sliding  rod, 
a  beautiful  and  continuous  cascade  of 
Fig.  236.  electric  light  will  pour  over  the  edge  of 

the  tumbler  upon  the  metallic  plate  of  the 
pump.  The  effect  is  heightened  if  the 
tumbler  be  placed  upon  a  glass  dish  wash- 
ed over  with  sulphate  of  quinine :  a  blue 
fluorescence  will  be  produced  which  will 
contrast  well  with  the  yellow  glass. — 
By  introducing  the  vapors  of  different 
substances  and  different  gases,  the  light 
of  the  electric  egg  is  entirely  changed,  and 
a  very  curious  stratified  light  produced, 
varying  with  the  substance  employed. 
The  best  method  of  procedure,  is  to  seal 
The  Uranium  Glass.  wires  of  platinum  into  the  extremities  of 
a  glass  tube,  introduce  the  gases,  and  then 
exhaust  the  tube  more  or  less  completely.  Thus,  if  a  long 
wide  glass  tube,  Fig.  236,  containing  sticks  of  caustic  potash, 
at  P,  be  filled  with  carbonic  acid  gas,  and  exhausted  by  the 
air-pump,  the  residual  carbonic  acid  will  then  be  absorbed  by 
the  potash,  and  the  vacuum  thus  made  very  nearly  perfect. 
The  effects  observed  on  connecting  the  wires  +  and  — ,  with 


Describe  No.  2 :  No.  3.    What  is  the  effect  of  using  an  Uranium  glass ' 
effect  of  employing  the  vaeua  of  different  gases? 


What  is  the 


OF  DIFFERENT  GASES. 

Fig.  236. 


469 


Luminous  effects  of  Ruhmkorff's  Coil  in  a  vacuum  of  Carbonic  Acid. 


the  poles  of  the  secondary  coil  of  Ruhmkorflf,  vary  with  the 
perfection  of  the  vacuum.  If  it  be  merely  that  which  can  be 
produced  by  an  ordinary  air-pump,  no  stratification  is  obtained, 
and  only  a  diffuse  lambent  light  fills  the  tube  ;  if  the  rarefaction 
be  carried  a  step  further,  narrow  striae,  like  ruled  lines,  traverse 
the  tube,  Fig.  237,  No.  1 :  a  further  rarefaction  increases  the 

Fig.  237. 


+  ? 


\'\  <jf ffl^^'f-Wf^^^frf-f—^^ 


t 

T  - 


Luminous  effects  varying  with  the  completeness  of  the  vacuum. 

breadth  of  the  bands :  if  pushed  still  further,  the  bands  assume 
a  cup-shaped  or  conical  form,  Fig.  237,  No.  2 ;  and  finally,  a 
series  of  luminous  cylinders,  with  narrow  dark  lines  between 
them,  Fig.  237,  No.  3 ;  lastly,  when  the  vacuum  approaches 
perfection,  all  the  discharge  and  light  absolutely  cease.  When 

Describe  the  effect  of  a  Carbonic  acid  vacuum  made  more  and  more  complete  ?    What 
is  the  effect  when  the  vacuum  is  perfect  ? 


470  GEISSLER'S  TUBES. 

the  stratification  is  most  distinct,  a  dark  space  appears  at  the 
negative  pole,  and  the  platinum  wire  is  seen  to  be  covered  with 
a  bluish  glow  of  light,  within  which  the  metal  glows  as  if  red 
hot :  as  the  experiment  is  continued  and  the  wire  rises  consid- 
erably in  temperature,  portions  of  the  negative  wire  are  grad- 
ually thrown  off  in  the  form  of  fine  metallic  particles.  The 
shape  and  color  of  the  stria3  vary  with  the  gases  employed.  In 
hydrogen  the  light  is  white  and  red  ;  in  carbonic  acid,  greenish ; 
in  nitrogen, orange  yellow.  The  light  furnished  by  hydrogen, 
nitrogen,  carbonic  acid,  and  other  gases,  give  different  spectra 
when  decomposed  by  the  prism  and  viewed  through  a  telescope. 
With  oxygen,  a  good  characteristic  spectrum  is  not  obtained, 
on  account  of  its  gradual  disappearance  and  combination  with 
the  platinum  of  the  pole ;  the  bi-oxide  of  nitrogen  is  decom- 
posed, giving,  after  a  brief  interval,  the  spectrum  of  pure  nitro- 
gen in  great  splendor ;  aqueous  vapor  is  decomposed,  and  the 
spectrum  of  hydrogen  produced :  with  ammonia,  the  spectra  of 
hydrogen  and  nitrogen  super-imposed,  are  obtained.  If  the 
vapor  of  spirits  of  turpentine,  pyroligneous  acid,  alcohol,  or  bi- 
sulphide of  carbon,  are  introduced  into  such  tubes  before  the 
exhaustion,  the  aspect  of  the  light  is  still  further  modified,  and 
some  very  magnificent  effects  obtained.  In  an  absolute  vacuum, 
the  current  does  not  pass  at  all,  the  transport  of  some  material 
particles  being  always  necessary  for  its  passage.  Glass  tubes 
containing  highly  rarefied  gases  and  vapors,  and  of  various 
forms  and  sizes,  are  constructed  with  great  ingenuity  by  M. 
Geissler,  of  Bonn,  and  may  be  procured  in  this  country  of  the 
principal  philosophical  instrument  dealers.  The  light  produced 
is  oftentimes  of  the  most  beautiful  and  varied  character,  and  the 
phenomena  are  sometimes  made  still  more  brilliant  from  the 
fluorescence  which  the  discharge  excites  in  the  glass. 

461.  The  Light  intermittent,  and  affected  by  the  Magnet. 
The  stratified  light  of  Ruhmkorff 's  coil  is  intermittent  in  its 
character,  on  account  of  the  nature  of  the  apparatus.  This  can 
be  shown  very  beautifully  by  causing  one  of  the  vacuum  tubes 
to  revolve  very  rapidly  upon  an  axle,  the  two  arms  projecting 
at  right  angles  to  the  axis,  like  the  spokes  of  a  wheel,  one  ex- 
tremity of  the  tube  being  in  constant  contact  with  one  end  of 
the  coil,  and  the  other  with  the  other  end.  As  the  rotation  goes 
on,  the  tube  will  be  visible  momentarily,  the  experiment  being 
made  in  the  dark,  several  times  during  each  revolution,  and 

What  is  the  effect  upon  the  platinum  wires  ?  What  is  the  color  in  Hydrogen  ?  in  Car- 
bonic acid  ?  in  Nitrogen  ?  Do  the  different  gases  give  different  spectra  when  their  light 
Is  decomposed  by  the  Prism  ? 


r   THE    LIGHT    AFFECTED    BY    THE    MAGNET.  471 

will  produce  the  appearance  of  a  star  of  light,  each  arm  of  the 
star  possessing  distinct  stratified  bands,  and  appearing  to  be  sta- 
tionary on  account  of  the  briefness  of  the  time  for  which  it  is 
visible.  The  phenomena  of  stratification  are  not  owing  to  the 
undulations  produced  by  the  rapid  succession  of  the  secondary 
currents,  for  the  same  effects  have  been  produced  from  a  water- 
battery  of  3,500  cells,  also  from  400  small  Grove's  cells ;  the 
quantity  transmitted  was  so  small,  that  the  amount  of  water  de- 
composed by  the  current,  as  estimated  by  a  voltameter,  §381,  was 
almost  inappreciable,  but  a  beautifully  distinct  stratification  was 
observed :  this,  however,  was  not  the  true  voltaic  arc ;  on  bring- 
ing the  two  polar  wires  of  the  battery  very  near  each  other, 
the  true  voltaic  arc  was  suddenly  established,  a  great  rise  of 
temperature  took  place,  and  the  arc  seen  to  be  also  distinctly 
stratified.  These  stratified  discharges  are  powerfully  affected 
by  the  magnet,  in  accordance  with  the  same  laws  with  which 
it  acts  on  all  movable  conductors:  if  one  of  the  exhausted 
tubes  be  suspended  vertically,  with  the  negative  pole  under- 
most, it  will  be  found  on  bringing  one  end  of  a  powerful 
magnet  near  the  extremity  of  one  of  the  band$,  in  the  direction 
of  the  axis  of  the  tube,  that  the  stratification  will  be  changed 
and  made  to  assume  the  appearance  of  a  luminous  spiral  spring 
stretched  out.  The  negative  pole  seems  to  be  specially  affected 
by  the  magnetic  force,  the  lines  of  light  assuming  a  position 
parallel  to  that  of  the  magnetic  curves,  §447.  It  has  also  been 
ascertained  by  Mr.  Gas -dot,  that  by  arranging  a  vacuum  tube 
so  as  to  cross  the  lines  of  magnetic  force  of  a  powerful  electro- 
magnet, the  discharge  can  be  instantly  arrested  by  magnetizing 
the  electro-magnet ;  and  by  de-magnetizing  the  magnet  thu 
discharge  is  immediately  renewed.  De  la  Rive  has  shown  that 
if  one  pole  of  a  powerful  bar  electro-magnet  be  introduced  into 
the  axis  of  an  electric  egg,  into  which  a  little  spirits  of  turpen- 
tine has  been  introduced,  and  then  exhausted,  the  electro-mag- 
netic bar  extending  up  to  the  centre  of  the  egg,  and  being 
covered  with  glass  in  such  a  way  that  the  electric  discharge  from 
Ruhmkorff 's  coil  is  compelled  to  pass  from  its  uppenextremity, 
over  the  glass,  to  a  copper  ring  at  the  bottom  of  the  egg,  pro- 
ducing a  more  or  less  irregular  flow  of  light  over  the  electro- 
magnet,— the  instant  the  electro-magnet  becomes  magnetized 
by  the  passage  of  the  battery  current,  the  light  ceases  to  stream 
from  every  point  of  the  upper  end  of  the  magnet,  and  is  con- 
Describe  the  spectra  of  different  gases. — 4f51.  How  can  the  light  he  proved  to  be  in. 
termittent  ?  What  effect  is  produced  by  the  magnet  ?  Describe  Gassiot's  experiments : 
De  la  Rive's. 


472 


THE   APPLICATIONS    OP 


densed  into  a  single  luminous  arc  extending  vertically  from  the 
top  of  the  magnet  to  the  bottom  of  the  egg,  and  then,  which  ia 
the  most  remarkable  part  of  the  experiment,  it  begins  to 
revolve  slowly  around  the  axis  of  the  magnet,  turning  in  one 
direction  or  the  other,  according  to  the  direction  of  the  current 
in  the  electro-magnet,  and  the  direction  of  the  current  from  the 
coil.  As  soon  as  the  magnet  is  de-magnetized,  the  vertical 
spark  disappears  and  resumes  its  even  flow.  This  is  thought 
to  prove  that  the  rotary  motion  from  east  to  west,  observed  in 
the  Aurora  Borealis,  may  be  referred  to  the  influence  of  terres- 
trial magnetism. 

462.  The  Application  of  Geissler's  Tubes  to  medical  pur- 
poses and  the  illumination  of  Mines.     The  light  of  Geissler's 
tubes  has  been  recently  applied  to  medical  purposes.     A  long 
capillary  tube,  a,  Fig.  238,  is  attached  to  two  bulbs,  provided 
with  platinum  wires :  this  tube  is  bent 
in  the  middle,  so  that  the  two  branches 
touch,  and  their  extremities  are  twist- 
ed at  a;  the  whole  is  filled  with   a 
highly  rarefied  gas.     On  the  passage 
of   the    current,   a   sufficiently  bright 
light  is  produced  at  a,  to   illuminate 
the  nostrils,  the  throat,  or  any  other 
cavity  of  the  body  into  which  the  tube 
may  be  introduced,  and  allow  of  its 
thorough  examination. 

M.  Gassiot  has  devised  a  simple 
modification  of  Geissler's  tubes  for  the 
purpose  of  illumination,  Fig.  239.  It 
consists  of  a  carbonic  acid  vacuum 
tube,  of  about  one-sixteenth  of  an 
inch  internal  diameter,  wound  in  the 
form  of  a  flattened  spiral.  The  wider  ends  of  the  tube?,  in 
which  the  platinum  wires  are  sealed,  are  almost  two  inches  in 
length,  and  half  an  inch  in  diameter,  and  are  shown  by  the 
dotted  lines.  They  are  enclosed  in  a  case  of  wood,  indicated 
by  the  outside  line,  leaving  the  spiral  only  exposed.  When 
the  discharge  from  Ruhmkorff's  coil  is  transmitted  through 
the  platinum  wires,  the  spiral  becomes  intensely  luminous,  ex- 
hibiting a  brilliant  white  light.  The  discharge  may  be  trans- 
mitted through  fourteen  miles  of  copper  wire,  from  a  coil  giving 

What  ia  this  thought  to  prove  in  regard  to  the  Aurora  Borealis  1— 462.   What  applica- 
tion has  been  made  of  Geissler's  tubes  to  Medicine?  to  illumination? 


RuhmkorffsCoil  applied  to 
Medicine. 


GEISSLER  S    TUBES. 


473 


Fig.  239. 


a  spark  one  inch  in  length,  without  diminishing  the  luminosity 
of  the  spiral.  The  application  of  this  light 
to  mining  purposes  has  been  suggested  by 
Dumas  and  Benoit.  They  have  succeeded 
in  constructing  a  battery  in  a  convenient  and 
portable  form,  of  sufficient  power  to  keep  up 
a  regu'ar  light  for  twelve  hours.  The  ad- 
vantage of  this  mode  of  illumination,  is,  that 
no  heat  is  emitted  by  the  light,  and  the  tube 
remains  cold:  the  gas  of  the  mine  has  no 
access  to  it,  so  that  there  is  no  danger  of  ex- 
plosion :  there  is  no  evolution  of  noxious 
gases  and  it  can  be  lighted  and  extinguished 
at  will. 

463.  Application  of  Ruhmkorff  "s  Coil  to 
spectrum  analysis.  One  of  the  most  inter- 
esting applications  of  Ruhmkorff 's  coil,  is 
to  the  determination  of  the  characteristic  lines 
exhibited  by  the  spectra  of  the  various  chem- 
ical elements,  §28o.  Most  of  the  metals 
require  a  higher  temperature  than  that  of 
common  flame,  in  order  that  their  vapors 
may  become  luminous,  but  they  may  be  heated 
up  to  the  requisite  degree  by  means  of  the 
e'.ectric  spark,  which  in  passing  between  two 
pieces  of  the  metal  in  question,  attached  to  the  poles  of  the  coll, 
volatilizes  a  small  portion,  and  heats  it  so  intensely  as  to  ena- 
ble it  to  give  off  its  peculiar  light.  The  permanent  gases  also 
give  characteristic  spectra,  as  above  described,  if  strongly 
heated  by  the  passage  of  the  electric  spark.  The  arrangement 
of  Ruhrnkorff's  coll  for  exhibiting  the  spectra  of  the  metals,  is 
shown  in  Fig.  240:  +  and  — ,  represent  the  positive  and  neg- 
ative wires  connected  with  the  two  poles  of  the  secondary  coll: 
C,  is  a  condenser,  consisting  of  two  sheets  of  tin-foil  separated 
by  a  gla-s  plate;  between  these  plates  and  each  polar  wire  a 
metallic  communication  is  formed,  as  shown  in  the  Fig.:  t,  is  a 
support,  the  shaft  of  which  consists  of  a  glass  rod :  o,  o,  are 
balls  made  of  the  metal  in  question,  and  constitute  the  true 
po'es  of  the  secondary  coil,  between  which  the  spark  passes :  s, 
is  the  spectroscope,  constructed  upon  the  same  plan  as  the  one 
previously  described,  Figs.  108,  110:  s,  is  a  screen  for  the  pro- 
tection of  the  eye  of  the  observer.  At  each  passage  of  the 

463.  How  is  Ruhmkorff 's  Coil  employed  for  spectrum  analysis  ?    Describe  Fig.  240. 


Rnhmknrff's  Coil  ap- 
plied to  Illumination. 


474  THE    COIL    APPLIED  TO    SPECTEUri    ANALYSIS. 

Fiff.    240. 


The  Spectrum  Examination  of  the  Metals  by  Ruhmkorff^s  Coil. 


spark,  portions  of  the  metal  of  the  balls  are  torn  off,  and  at  the 
same  moment  intensely  heated,  and  made  to  emit  its  peculiar 
light,  which  is  then  viewed  by  ihe  telescope  through  the  pi  ism. 
For  the  determination  of  the  spectra  of  the  gases,  it  is  only 
necessary  to  direct  the  spectroscope  to  the  light  emitted  when 
the  electric  current  of  the  coil  is  transmitted  through  the  ex- 
hausted tubes  already  described.  For  a  full  description  of  the 
spectra  of  the  metals,  see  §285,  28G,  287. 

464.  Chemical  Effects.  The  chemical  effects  of  Ruhm- 
korff 'a  coil  are  quite  singular  and  very  different  from  those  of 
the  battery.  This  is  owing  to  the  fact,  that  the  secondary  cur- 
rent possesses  the  double  qualities  of  electricity  of  quantity, 
like  that  of  the  battery,  and  electricity  of  intensity,  like  that  of 
the  machine.  Now  it  is  well  known  that  the  chemical  act'on 
of  electricity  is  very  different  when  it  is  electricity  of  intensity, 
and  acts  interruptedly  by  means  of  sparks,  or  electricity  oi' 
quantity  acting  in  a  continuous  current.  In  the  first  care,  the 
decomposing  action  of  electricity  of  intensity,  like  that  famished 
by  the  electrical  machine,  is  to  discharge  a  mixture  of  both 

How  are  the  spectra  of  the  Gases  determined  ? — 464.   State  the  chemical  effects  o< 
Ruliiu korff  's  coil. 


THE    CHEMICAL 


475 


oxygen  and  hydrogen  at  loth  poles,  while  in  the  last  case,  the 
decomposing  action  of  electricity  of  quantity,  is  to  completely 
separate  the  two  gases  and  set  free  one  at  each  pole:  conse- 
quently, as  the  secondary  current  produced  by  Rnhmkorff's 
coil,  partakes  of-  the  qualities  of  electricity  both  of  quanti'y 
and  intensity,  it  might  be  expected  that  its  chemical  effects 
would  be  very  various.  Thus,  according  to  the  form  of  the 
pi  itinuin  poles  introduced  into  acidulated  water,  their  distance 
f  oin  each  other,  and  the  degree  of  acidulatioh  in  ihe  water, 
luminois  discha  ges  may  be  obtained  between  the  pole-,  with- 
out de  -ompo  ition  of  the  water,  or  decomposition  of  the  water 
with  the  separation  of  the  gases  from  each  o'her,  and  their  dis- 
cha'ge,  one  at  each  pole,  similar  to  the  decomposing  effects  of 
the  galvanic  current,  or  decomposition  of  water  with  the  gases 
mixed  and  discharged  at  the  same  pole,  theie  being  no  action 
at  the  other ;  or,  finally,  decomposition  of  the  water  and  the 
ga^es  set  free  mixed  at  both  poles. 

Ga  es  may  al  o  be  combined,  and  the  compound  gases  and 
vapors  deco  npo  ed  by  the  action  of  the  spark  of  the  secondary- 
current.  Tims,  if  a  tube  filled  with  air  be  hermetically  sealed, 
as  in  Fig.  241,  the  oxygen  and 
nitrogen  of  the  air  combine 
uu.ler  the  influence  of  the  cur- 
rent, and  at  the  end  of-  fen 
minutes  to  an  hour-it  is  filled 
with  orange  colored  vapors  of 
nitrous  acid.  This  experiment 
illustrates  the  formation  of  ni- 
tro  is  acid  in  the  atmosphere 
under  the  influence  of  elec- 
tricity. If  oxygen  be  enclosed 
in  a  tube  with  a  rotation  of 
starch  and  iodide  of  po'assiurn, 
as  in  Fig.  242,  and  a  suc- 
cession of  sparks  be  parsed 
through  it,  one  by  one,  the 
m'xture  will  soon  exhibit  the  characteristic  blue 
color  of  that  peculiar  modification  of  oxygen 
called  o 'one :  the  sparks  must  succeed  each  orirfn  convert, 
other  slowly  and  gently.  This  experiment  is  also  **  irtff>  (>--">»', 

.    .  .  i         •  i  i  i  •   i     •         &'/  KuJankorff  :4 

interesting  as   showing   that    the  ozone  which  is      coil. 


Fig.  241. 


Fig.  242. 


Conversion  of  Air  ints 
Nitrous  Arid,  by 
RukmkorJf'aUoil. 


How  do  electricity  of  intensity  and  quantity  differ  in  decomposing  power?    What  i* 
the  effect  of  the  coU  on  Air  ?  on  Oxygen  ? 


47$  EFFECTS    OF 

found  to  exist  in  the  air,  may  also  be  due  ta  the  action  of 
electricity  on  the  atmosphere.  The  passage  of  the  .spa:k 
through  compound  gases  and  vapurs,  is  attended  by  a  par- 
tial separation  of  their  component  elements:  in  the  case  of 
steam,  oxygen  appears  at  the  positive  pole,  and  hydrogen  at  the 
negative ;  and  long  sparks  are  found  to  be  more  effectual  in 
producing  decomposition,  than  short  ones.  Thus,  in  Fig.  "243, 

Fte.  243. 


Decomposition  of  Steam  by  Rukmkorff's  Coil. 

A,  is  a  half-pint  flask,  with  a  cork  in  which  three  holes  are 
bored;  in  one  of  these  is  inserted  the  glass  tube  B,  which  dips 
beneath  the  lower  end  of  H,  in  the  tough  of  water  c;  in  the 
others,  the  gla^s  tubes  D  and  E,  are  inserted,  enclosing  platinum 
wires  projecting  about  one  inch  into  the  flask,  and  appi cach- 
ing within  1-1 6th  of  an  inch  of  each  other,  FO  that  the  spark 
may  readily  pass  between  them:  D  and  E,  are  connected  by 
wires  with  the  poles  of  Ruhmkorff's  coil  R.  The  water  in  the 
flask  is  boiled  about  fif  een  minutes,  until  all  the  air  which  it 
contains  has  been  displaced  by  steam  ;  when  this  is  the  cafe, 
the  bubbles  of  steam  will  condense  in  c,  and  no  bubbles  of  air 
rise  into  the  inverted  tube  H,  filled  with  water :  if  at  this  mo- 
ment, the  water  still  boiling,  the  commutator  of  the  co'l  be 
turned  so  as  to  establish  a  connection  with  the  battery,  spaiks 
will  flash  through  the  steam  in  A,  decomposing  it,  and  filling 
the  tube  H  with  a  mixture  of  oxygen  and  hydrogen,  which  may 
be  tested'  by  clo-ing  the  tube  with  the  thumb  and  applying  a 
lighted  mntch ;  a  sharp  detonation  will  take  place.  The  power 
<  ?  the  secondary  induced  current  in  effecting  the  combination 
or  decomposition  of  gases  and  vapors,  is  much  greater  than  that 

What  is  the  effect  on  the  vapor  of  Water  ?    Describe  Fig.  243. 


THE    COIL.  477 

r 

of  the  ordinary  cylinder  or  plate  electrical  machine.  As  the 
condenser  simply  increases  the  intensity  of  the  electricity  of  the 
secondary  wire,  and  not  its  quantity,  no  gain  in  the  amount  of 
the  substance  decomposed  is  effected  by  its  use. 

465.  The  conversion  of  Carbon  into  the  Diamond  by  the 
long-continued  action  of  the  Coil.  M.  Despretz,  who  for  a 
long  time  has  been  engaged  in  experiments  upon  the  effect  of 
heat  on  carbon,  is  said  to  have  succeeded  in  converting  carbon 
into  diamonds  by  the  action  of  the  induced  current  of  Ruhm- 
korff's  coil.  He  fastened  a  small  piece  of  sugar,  which,  as  is 
well  kno  ,vn,  contains  a  large  amount  of  carbon  in  a  state  of  ab- 
solute purity,  to  the  lower  positive  ball  in  the  electric  egg,  and 
to  the  upper  ball  a  tuft  of  very  fine  platinum  wire  for  the  pur- 
pose of  catching  the  sublimed  carbon.  A  vacuum  was  then 
produced  and  the  electric  current  allowed  to  traverse  the  appa- 
ratus for  several  months.  At  the  end  of  this  time  the  plati- 
num wires  were  found  to  be  covered  with  fine  black  powder,  in. 
which  were  discovered  traces  of  crystallization.  Among  these 
crystals,  ,<=ome  were  found  of  a  black  color,  others  were  perfectly 
translucid,  and  were  found*  to  be  regular  octoedra  of  a  pyramidal 
form.  When  examined  by  a  lapidary,  they  were  found  to  be 
possessed  of  all  the  properties  of  the  diamond.  Rubies  were 
very  quickly  polished  with  their  powder,  and  the  crystals 
burned  in  air  without  leaving  any  residue. 


465.  Magneto-Electric  Machines.  —  The  principles  on 
which  they  depend.  These  are  machines  for  generating  cur- 
rents of  electricity  by  the  revolution  of  coils,  in  front  of  the 
poles  of  powerful  permanent  or  electro-magnets.  In  Page's 
and  Ruhmkorff 's  colls,  the  secondary  current  is  produced  partly 
by  the  inductive  influence  of  the  primary  current,  and  partly  by 
that  of  the  electro-magnet.  In  the  magneto-electric  machine, 
the  electric  current  is  produced  by  the  inductive  influence  of 
powerful  permanent  magnets.  By  bringing  a  magnet  near  a 
coil  composed  of  fine  covered  wire  and  forming  a  closed  cir- 
cuit, it  has  been  shown,  §442,  Fig.  219,  that  a  momenta1""1 
current  of  electricity  is  induced ;  and  again,  that  when  such 
magnet  is  removed  from  the  coil,  another  momentary  current, 
in  the  opposite  direction,  is  induced.  It  has  also  been  stated, 
that  the  two  poles  of  the  magnet  induce  currents  in  opposite  di- 

465.  What  is  the  effect  of  the  coil  on  Carbon?    Describe  Despretz'  experiments.— 466. 
What  are  Magneto-Electric  Machines  ?    How  is  the  Electric  current  produced? 


478  MAGNETO-ELECTRIC 

rections,  i.  e.,  if  the  north  pole  of  the  magnet  be  introduced  into 
the  coil,  Fig.  219,  and  a  current  observed  to  flow  from  left  to 
right,  as  shown  by  the  galvanometer,  and  then  the  north  pole  be 
withdrawn  and  the  south  pole  be  introduced,  a  current  of  elec- 
tricity will  be  induced  in  the  opposite  direction,  or  from  right  to 
left : — moreover,  that  these  effects  are  reversed  if  the  direction 
of  the  winding  is  changed  ;  i.  e.,  if  the  north  pole  of  the  magnet 
be  introduced  into  a  right  hand  coil,  the  current  will  be  in  the 
inverse  direction  to  that  which  is  induced  when  the  same  pole 
is  introduced  into  a  left  hand  coil:  if  the  south  pole  of  the 
magnet  be  employed  instead  of  the  north  pole,  the  same  results 
follow  ;  so  that  if  two  coils  are  wound  in  the  same  direction,  and 
placed  side  by  side,  and  a  north  pole  of  a  magnet  be  introduced 
into  one  coil,  and  a  south  pole  into  the  other  simultaneously,  a 
current  will  be  induced  in  each  coil,  in  opposite  directions :  but 
if  the  coils  are  wound  in  opposite  directions,  and  a  north  pole  bo 
introduced  into  one,  and  a  south  pole  in'o  the  other  at  the  same 
moment,  a  current  will  be  induced  in  each  in  the  same  direction. 
This  is  equally  true,  if  instead  of  introducing  permanent  mag- 
nets into  the  coll-,  these  are  wound  upon  soft  iron  cores,  and  then 
the  cores  are  magnetized  and  de-magnetized  by  the  inductive  ac- 
tion of  powerful  permanent  magnets  suddenly  brought  near  and 
removed  from  their  extremities.  Consequently,  if  a  coil  of  fine 
insulated  wiie  be  wound  u|*>n  a  core  of  soft  iron,  and  a  powerful 
permanent  magnet  be  presented  to  one  extremity  of  the  iron 
core,  first  by  one  pole,  and  then  by  the  other,  the  soft  iron  will 
become  magnetized  and  de-magnetized,  upon  every  approach  and 
removal  of  the  magnet ;  and  a  current 
Fig.  244.  of  electricity  made  to  circulate  through 

the  coil,  first  in  one  direction  and  then 
in  the  other.  If  there  are  two  such 
pieces  of  soft  iron,  with  coils  wound  in 
opposite  directions,  and  having  the  ends 
of  the  wires  soldered  together  so  as  to 
form,  in  effect,  but  one  closed  circuit, 
and  the  north  and  south  pole  of  a 
horse-shoe  magnet  be  presented  at  the 
same  moment  to  both,  they  will  become 
oppositely  magnetized,  and  a  momentary 
current  of  electricity  in  the  same  direc- 
tion  be  induced  in  each  coil  at  every  ap- 

Why  imist  the  coils  be  wound  in  opposite  directions  ?    Describe  the  successive  effects 
which  take  place  when  the  wound  armature,  c,  Fig.  244,  is  made  to' revolve. 


MACHINES.  479 

proach  and  removal  of  the  magnet.  If,  then,  in  Fig.  244,  N  and 
s  be  the  poles  of  a  powerful  magnet  firmly  fixed,  and  C,  a  horse- 
shoe armature,  wound  with  two  coils  of  fine  wire  in  opposite 
directions,  having 'their  ends  connected  so  as  to  form  a  closed 
circuit,  and  arranged  to  revolve  about  a  vertical  axis,  so 
that  A,  after  half  a  revolution,  will  be  above  s,  and  B  above  N, 
it  is  evident  that  so  long  as  the  armature  is  at  rest,  it  is  magnet- 
ized by  the  inductive  influence  of  the  permanent  magnet,  the 
po!es  being  reversed ;  but  the  instant  the  armature  beg'ns  to 
revolve,  it  is  de-magnetized,  and  a  momentary  current  of  elec- 
tricity is  induced  in  the  coils,  which  entirely  ceases  by  the  time 
it  has  made  a  quarter-revolution.  Were  the  coils  wound  in  the 
same  direction,  the  momentary  currents  circulating  in  each, 
would  move  in  opposite  directions ;  but  as  they  are  wound  in 
opposite  directions,  momentary  currents  in  the  same  direction 
arc  induced  in  both.  As  the  armature  moves  beyond  the  quar- 
ter-revolution, and  its  extremities  approach  the  poles  of  the 
permanent  magnet,  they  again  become  magnetized  by  induction, 
and  it  inii>-lit  be  supposed  that  an  electrical  current  would  be 
induced  in  each  coil,  in  a  contrary  direction  to  what  it  was  in  the 
first  quarter-revolution,  because,  as  we  have  seen,  the  currents 
induced  by  removing  the  magnet  from  a  coil  and  restoring  it,  are 
always  in  the  opposite  direction ;  but  as  the  extremities  of  the 
armature  are  now  approaching  reverse  poles,  this  effect  is  neu- 
tralized, and  the  new  currents  of  electricity  induced  in  the  coils 
in  the  second  quarter-revolution,  are  in  the  same  direction  with 
those  in  the  first  quarter,  so  that  in  making  half  a  revolution 
each  coil  experiences  the  induction  of  two  currents  of  electricity 
in  tho  same  direction,  in  consequence  of  receding  from  and 
approaching  opposite  poles,  alternately  in  the  two  quarter- 
ro  volutions,  at  the  same  moment.  In  the  second  half -revo- 
lution, two  currents  of  electricity  are  induced  in  the  same 
direction  in  each  coil,  but  directly  opposite  to  those  induced 
in  the  same  coils  in  the  first  half,  because  the  coils  are  now 
receding  from  and  approaching  the  reverse  po!es,  N  and  s  hav- 
ing interchanged  places  in  reference  to  A  and  B.  Consequently, 
if  c.  were  made  to  revolve  continuously  around  N  and  s,  a  suc- 
cession of  currents,  in  opposite  directions,  in  each  half -revolution 
alternately,  would  be  made  to  circulate  through  both  coils.  In 
order  that  this  effect  may  be  produced,  it  is  necessary,  as  has 
been  stated,  that  the  ends  of  the  coils  should  be  connected  at 

How  many  currents  are  induced  in  every  half-revolution  ?     Why  may  these  be  re- 
garded as  only  one  current  ?     What  is  the  final  result  ? 


480  SAXTON'S 

both  their  extremities,  so  as  to  form  a  closed  circuit ;  and  on 
introducing  a  galvanometer  into  this  circuit,  these  effects  may 
be  traced  by  the  oscillations  which  are  imparted  to  the  needle. 
The  currents  thus  induced  are  primary  currents,  and  are  not 
sufficiently  intense  to  produce  powerful  shocks.  For  this  pur- 
pose it  is  necessary  that  the  circuit  be  broken  at  the  exact  mo- 
ment in  each  half-revolution  when  the  induction  of  the  pri- 
mary current  takes  place.  This  break  in  the  primary  current 
produces  in  the  coils  a  direct  extra-current,  §  438,  of  extreme 
intensity,  moving  in  the  same  direction  as  the  primary,  and 
greatly  increasing  its  power.  When  this  extra  current  thus 
induced,  is  transmitted  through  the  body,  the  shocks  become 
almost  insupportable,  and  if  directed  through  carbon  points,  the 
sparks  acquire  great  brilliancy.  For  the  production  of  chemi- 
cal decomposition,  however,  the  primary  current  is  sufficiently 
powerful,  and  no  break  in  the  circuit  is  required.  These  effects 
are  manifested  both  at  the  removal  and  approach  of  the  coils, 
but  more  vividly  at  the  removal  than  at  the  approach,  and  their 
vividness  is  proportioned  to  the  suddenness  of  the  break  in  the 
circuit,  and  the  rapidity  of  the  revolution  of  the  coils. 

467.  Saxton's  Magneto-Electric  Machine.  The  first  mag- 
neto-electric machine  for  the  production  of  continuous  currents 
of  electricity,  was  made  by  M.  Pixii  at  Paris,  in  1832 :  it  con- 
sisted of  two  coils  of  insulated  wire  wound  upon  iron  cores,  in 
front  of  which,  the  poles  of  a  powerful  magnet  were  made  to 
revolve  with  great  rapidity.  In  1833,  Mr.  Saxton,  of  Phila- 
delphia, invented  a  machine  of  much  greater  power  than  that 
of  Pixii,  in  which  a  curved  armature  with  its  coils,  like  that 
represented  in  Fig.  244,  was  rapidly  revolved  before  the  po'es 
of  very  powerful  permanent  magnets.  It  is  represented  in  Fig. 
245,  and  a  section  of  the  armature  and  its  coils  in  Fig.  246. 
It  consists  of  a  powerful  horse-shoe  magnet,  M,  placed  horizon- 
tally upon  one  of  its  sides :  in  front  of  its  poles,  and  as  clo-e  to 
them  as  possible,  without  actual  contact,  an  armature  of  soft 
iron  is  made  to  revolve  upon  a  horizontal  axis,  which  admits 
of  being  turned  with  great  rapidity  by  means  of  a  cord  passing 
over  a  multiplying  wheel,  w.  This  armature  consists  of  a  curved 
piece  of  iron  of  such  a  shape  that  its  two  extremities,  a  and  b, 
are  at  the  same  distance  apart,  as  the  two  poles  of  the  magnet, 
and  each  carries  a  coil  of  very  fine  wire,  c  and  «?,  careiully 
insulated.  The  two  extremities  of  the  wires  which  form  the 

Why  must  the  continuity  of  the  circuit  be  interrupted  in  order  to  display  the  cur- 
tents  1    Is  the  effect  more  powerful  on  the  approach  or  removal  of  the  coila  ? 


MAGNETO-ELECTRIC 
I  Fig.  245. 


481 


Saxton's  Magneto-Electric  Machine, 


Fig.  246. 


Armature  and  Coils  of  Saxton's  Machine. 

^rminations  of  the  coils,  h  and  #,  are  united  and  soldered  to 
a  piece  of  copper  passing  through  the  axis' of  the  spindle  on 
which  the  armature  rests,  but  insulated  from  it,  and  termi- 
nating in  the  copper  cross-piece,  &,  which,  at  every  half-revolu- 
tion clips  into  the  mercury  cup,  /,  and  immediately  emerges  from 
it  again,  thus  breaking  and  completing  the  circuit  once  in  every 
half-revolution;  the  other  ends  of  the  coils,  eand/,  are  soldered 
to  the  spindle  it?elf,  and  terminate  in  the  circular  disc  of  copper, 
t,  which  revolves  in  the  mercury  cup,  m,  thus  maintaining  a 

437.  Describe  Saxton's  Machine.    How  many  currents  are  produced  at  every  revolu- 
tion of  the  coils  ? 


482  MACHINE. 

constant  connection  between  it  and  the  extremities  of  the  wires 
which  form  the  commencement  of  the  coils.  The  two  mercury 
cups,  I  and  m,  are  insulated  from  each  other,  but  may  be  con- 
nected by  a  curved  wire.  This  curved  wire  being  inserted,  it  is 
evident  that  when  either  of  the  ends  of  k  are  immersed  in  the 
mercury  cup,  /,  a  closed  circuit  is  formed,  of  which  the  coils  and 
the  two  mercury  cups  form  parts,  and  that  whenever  the  cross- 
piece  emerges  from  the  mercury  the  continuity  of  the  circuit  is 
broken,  and  the  extra-electric  current  has  an  opportunity  to  mani- 
fest itself.  The  cross-piece,  k,  is  so  arranged  that  its  ends  shall 
emerge  from  the  mercury  and  break  the  circuit  at  the  moment 
when  the  coils  have  just  left  the  poles  of  the  permanent  mag- 
net to  which  they  have  been  opposed.  Under  these  circum- 
stances, if  the  wheel,  w,  in  Fig.  245,  be  rapidly  turned,  four 
momentary  currents  of  induced  electricity,  two  negative  and 
two  positive,  which  may  be  regarded  as,  in  effect,  but  two,  one 
negative  and  the  other  positive,  will  flash  through  the  wires  in 
opposite  directions,  at  every  revolution  ;  and  these  will  be  made 
manifest  by  bright  sparks  of  light  whenever  either  arm  of  k 
emerges  from  the  mercury  cup,  /.  If  the  wire  connecting  the 
insulated  mercury  cups  be  removed,  and  wires  inserted  inio 
them,  connected  with  the  two  metallic  handles,  H,  H,  which 
may  be  grasped  by  the  hands,  then  these  handles  and  the 
bystander  become  a  part  of  the  closed  circuit,  and  at  every 
revolution  of  the  coils,  four  currents  of  electricity,  in  opposite 
directions,  the  first  two  in  one  direction,  and  the  second  two  in 
the  opposite,  will  flash  through  his  body,  producing  an  insup- 
portable torrent  of  shocks.  If  the  wires  leading  from  the 
two  mercury  cups  be  attached  to  a  galvanometer,  the  needle 
will  be  violently  deflected,  twice  in  each  revolution,  first  in 
one  direction,  and  th'-n  in  the  other,  by  the  two  opposite  cur- 
rents. If  they  be  tipped  with  platinum,  and  dipped  in!o  a 
solution  of  acidulated  water,  this  will  be  decompo-ed,  oxygen 
set  free  at  the  positive  wire,  and  hydrogen  at  the  negative, 
in  each  half-revolution ;  but  as  the  positive  and  negative  cur- 
rents in  each  half-revolution  are  in  opposite  directions,  each 
9  polar  wire  becomes  alternately  positive  and  negative,  and  the 
oxygen  in  the  second  half-revolution  appears  at  the  same  wire 
as  the  hydrogen  in  the  first,  and  the  hydrogen  in  the  second 
at  the  same  wire  with  the  oxygen  in  the  first ;  these  imme- 
diately re-combine,  and  thus  the  chemical  effect  of  the  first  half- 
Why  may  these  be  regarded  as  in  effect  hut  two?  Explain  why  the  poles  are  alter- 
nately affected  with  opposite  kinds  of  electricity.  What  are  the  physiological  effects?  the 
effects  upon  the  maguet?  the  chemical  effects? 


PAGE  S 


483 


revolution  is  neutralized  by  that  of  the  second.  In  order  to 
obviate  this  difficulty,  it  is  necessary  to  turn  up  one  of  the  arms 
of  kt  so  that  it  will  not  touch  the  mercury,  and  thus  suppress 
the  current  in  every  alternate  half  revolution.  By  this  ar- 
rangement, only  two  momentary  electrical  currents  are  produced 
in  every  revolution ;  but  as  they  are  both  in  the  same  direc- 
tion, and  of  the  same  kind,  the  poles  are  not  alternately  rev- 
ersed. The  power  of  the  machine  is  thus  reduced  one-half; 
but  thus  arranged,  this  current  of  induced  electricity  may 
be  used  to  produce  chemical  decomposition,  in  the  same  man- 
ner as  the  current  from  an  ordinary  galvanic  battery. 

468.  Pace's  Magneto-Electric  Machine.  The  mercurial 
cups  in  the  instrument  just  described  alternately  receive  a  cur- 
rent of  positive  and  negative  electricity,  but  by  the  use  of  a 
pole-changer,  their  connection  with  the  wires  which  terminate 
the  coils  may  be  changed  twice  in  every  revolution,  and  thus 
the  electricity  of  each  cup  be  made  constantly  the  same,  and  a 
continuous  flow  of  electricity  of  the  same  kind  maintained  from. 
each  cup,  that  may  be  u.sed  for  any  of  the  purposes  for  which 
the  electrical  current  of  the  battery  is  generally  employed. 
This  object  is  best  accomplished  in  Page's  magneto-electric  rna- 


Page's  Magneto-Electric  Machine. 

chine,  Fly.  247 :  M,  M,  are  two  powerful  permanent  magnets, 
arranged  one  above  the  other  in  such  a  manner  that  the  north 
pole  of  the  upper  magnet  is  above  the  south  pole  of  the  lower, 

Why  must  the  current  in  every  alternate  half -re  volution  be  suppressed?  What  effect 
has  this  upon  the  power  of  the  machine? — 468.  Describe  Page's  machine.  How  are  the 
coils  mounted  ? 


48  1 


MAGNETO-ELECTRIC 


and  the  south  pole  of  the  upper  ahove  the  north  pole  of  the 
lower  :  A,  A,  are  two  armatures,  each  wound  with  a  coil  of  fine 
wire  in  opposite  directions,  and  mounted  vertically  between  the 
magnets,  so  that  their  iron  cores  are  exposed  at  both  extrem- 
ities simultaneously  to  the  inductive  influence  of  the  opposite 
poles  of  both  magnets,  instead  of  one  extremity  only,  as  in 
Saxton's  machine,  and  become  much  more  powerfully  magnet- 
ized :  these  coils  have  their  extremities  connected  with  oppo- 
site sides  of  the  pole-changer  attached  to  the  vertical  shaft,  on 
Avhich  the  coils  are  made  to  revolve  by  the  wheel  w  ;  P,  N,  are 
binding  cups,  filled  with  mercury,  insulated  from  the  magnets 
and  each  other,  and  connected  with  the  pole-changer  by  wires 
which  press  tightly  upon  its  surface.  At  every  half-revolution 
the  direction  of  the  electrical  current  flowing  through  the  coils 
is  changed,  and  those  extremities  of  the  coils  which,  at  the  pre- 
ceding half-revolution,  discharged  a  positive  current,  now  dis- 
charge a  negative  one;  at  the  instant  that  this  change  takes 
place,  their  connection  with  the  cups  is  changed,  and  the  ends 
which  formerly  gave  off  positive  electricity,  but  now  negative, 
become  connected  with  the  cup  which  then  received  the  negative 
current,  and  the  ends  which  formerly  gave  off  negative  electri- 
city, but  now  positive,  become  connected  with  the  cup  which  rhen 
received  the  positive  current  ;  consequently,  each  cup  receives, 
and  gives  off,  the  same  kind  of  electricity  in  the  second  half- 
revolution,  as  in  the  first.  This  change  of  the  ends  of  the  coils 
is  effected  by  the  pole  changer,  represented  in  Fig.  248  :  s,  rep- 

resents a  cross  sec- 

Fig.  248.  tion  of  the  vertical 

shaft  on  which  the 
armatures  revolve; 
A  and  B,  are  two 
pieces  of  brass, 
which  encircle  the 
shaft,  but  are  sep- 
arated from  it  by 
some  non-conduct- 
ing  material;  they 
are  also  insulated 
from  each  other  by  the  bits  of  ivory,  i,  i;  the  wires  which 
begin  the  coils  are  firmly  fastened  to  A,  and  those  which 
terminate  them,  to  B  :  P  and  N  represent  wires  connected 


How  is  the  electricity  of  each  cup  kept  constantly  the  same?    Describe  the  Pole- 
changer. 


,  MACHINE.  485 

with  the  corresponding  mercury  cups,  pressed  tightly  agamst 
the  brass  pieces,  A  and  B.  As  the  shaft  revolves,  A  and  B 
revolve  with  it  and  the  coils ;  the  instant  that  the  half-revo- 
lution is  teiminated,  the  direction  of  the  current  reversed,  and 
A  begins  to  discharge  negative  electricity,  instead  of  positive, 
the  connection  of  A,  with  the  positive  wire  and  cup  p,  ceases, 
in  consequence  of  the  revolution,  and  is  established  with  the 
negative  wire  and  cup  N  ;  at  the  same  instant,  B  is  ceasing 
to  discharge  negative  electricity,  and  beginning  to  discharge 
positive,  and  its  connection  with  the  negative  wire  N  is  broken, 
and  established  with  the  positive  wire  P.  By  this  simple  ar- 
rangement, the  two  cups,  P  and  N,  are  made  to  di-charge  inter- 
mittent momentary  currents  of  the  same  kind  of  electric  ty, 
which  approach  more  nearly  a  continuous  flow,  as  the  revolu- 
tion of  the  coils  becomes  more  rapid,  and  by  combining  several  of 
these  machines  whose  armatures  are  so  arranged  that  each  shall 
in  turn  become  mngiietized  just  before  the  preceding  one  has  en- 
tirely lost  its  magnetism,  magneto-electric  machines  have  been 
constructed  by  which  a  continuous  current  in  a  uniform  direction 
can  be  steadily  maintained.  The  break  required,  p.  406,  for  giv- 
ing severe  shocks  is  made  by  a  wire  pressing  upon  a  toothed 
wheel,  Fig.  247.  This  is  removed  when  the  instrument  is  used 
for  chemical  decomposition.  See  Expts.,  160, 170,  p.  541. 

469.  Magneto-lSlcctricity  used  in  the  Arts,  in  place  of 
Voltaic  Electricity,  especially  for  the  illumination  of  Lig-ht- 
houses.  As  the  electrical  current  induced  by  magnetism 
possesses  all  the  decomposing,  heating  and  physiological  pow- 
ers of  the  electricity  of  the  battery,  and  is  much  more  man- 
ageable, because  produced  by  a  definite  amount  of  motion,  it 
is  often  substituted  for  the  electricity  of  the  battery,  in  electro- 
plating. A  single  Saxton's  machine,  if  kept  in  continuous 
revolution,  will  precipitate  from  90  to  120  ounces  of  silver 
per  week,  from  its  solutions,  and  machines  have  been  constructed 
by  which  2J  ounces  of  silver  per  hour,  have  .been  deposited 
upon  articles  properly  prepared.  They  are  employed  with 
great  advantage  by  physicians,  for  the  administration  of  elec- 
tricity to  their  patients,  on  account  of  the  facility  with  which  the 
rapidity  of  the  shocks  may  be  regulated  by  the  motion  of  the 
wheel.  They  are  also  sometimes  made  use  of  for  telegraphic 
purpo  ;es,  where  an  occasional  message  only  is  to  be  sent,  as  in 
the  case  of  the  fire-alarm  of  cities  for  transmitting  the  alarm 
fro.n  the  central  office  to  every  district  of  the  city. 

4^9.  What  apnli^ations  have  been  made  of  Magneto-Electric  machines?    What  results 
have  bee.i  attained  in  electro-plating?  in  Light-house  illumiaation? 


486  MAGNETO-ELECTRICITY   APPLIED    TO  , 

These  machines  have  also  been  employed  for  the  production 
of  a  permanent  electric  light  between  two  pieces  of  gas-coke, 
for  Light-house  illumination ;  the  light  can  be  maintained  with- 
out interruption,  so  long  as  the  magnetic  armatures  are  kept  in 
rotation,  and  the  charcoal  remains  unconsumed.  Many  attempts 
have  been  made  to  use  the  intense  light  produced  by  the  carbon 
poles  of  a  powerful  Galvanic  battery  tor  the  same  purpose. 
When  these  poles,  as  has  been  shown,  §354,  after  having  been 
brought  into  contact,  are  slightly  separated,  even  in  a  vacuum, 
a  light  of  extraordinary  brilliancy  is  produced :  Despretz  has 
calculated  that  the  light  emitted  by  ninety-two  of  Bunsen's 
elements,  arranged  in  two  series  of  forty-six  each,  is  equal  to 
that  of  1,144  candles,  and  is  to  the  light  of  the  sun  as  1  to  2£ ; 
and  the  light  emitted  by  two  hundred  and  fifty  element?,  in  a 
grand  experiment  made  by  Profs.  Cooke  ai  d  Rogers,  in  the 
cupola  of  the  State  House,  Boston,  was  calculated  to  be  equal 
to  that  of  ten  thousand  candles.  Notwithstanding  the  intensity 
of  this  light,  from  the  difficulty  of  maintaining  a  perfectly  con- 
stant action  in  the  battery,  it  is  too  irregular  to  admit  of  suc- 
cessful use  for  the  illumination  of  Light-houses,  and  although 
tried  under  every  conceivable  circumstance,  it  has  thus  far 
proved,  for  these  purposes,  a  complete  failure.  In  the  mag- 
neto-electric machine,  in  which  the  current  is  produced  by  a 
perfectly  regular  mechanical  motion,  much  greater  success 
has  been  attained.  A  machine  for  this  purpose  was  first  con- 
structed by  Nollet,  at  Brussels,  in  1850,  and  was  afterwards 
improved  by  Van  Malderen.  .This  machine  is  represented  in 
Fig.  249.  It  consists  of  a  cast  iron  frame,  5|  feet  high,  on  the 
outside  of  which  eight  series  of  five  powerful  horse-shoe  mag- 
nets, A,  A,  A,  are  arranged  on  wooden  cross-pieces.  Upon  a  hori- 
zontal iron  axis  extending  from  one  end  to  the  other  of  the 
frame  four  bronze  wheels  are  fastened,  carrying  1C  coils  each, 
wound  with  138  yards  of  insulated  copper  wire.  These  coils 
are  made  to  revolve  in  front  of  the  poles  of  the  permanent 
magnets  by  an  endless  band,  which  receives  its  motion  from  a 
steam  engine  not  seen  in  the  Fig.  To  obtain  the  greatest  de- 
gree of  light,  the  most  suitable  velocity  is  235  revolutions  per 
minute.  By  this  rapid  revolution,  magneto-electric  currents 
of  high  intensity  are  induced,  which,  by  the  two  binding  screws 
a  and  6,  are  conducted  by  means  of  long  copper  wires,  to  two 
carbon  points  attached  to  the  sockets  of  one  of  Duboscq's  elec- 

What  advantage  has  this  inodc  of  illumination  over  the  Galvanic  Battery? 


THE    ILLUMINATION    OF    LIGHT-HOUSES.  487 

•    i 
Fig.  249. 


The  Illumination  of  Light-houses. 

trie  lamps,  §356,  as  shown  in  the  Fig.,  mounted  upon  the 
top  of  the  Light-hou-e  Tower.  In  this  machine,  the  current 
in  each  wire  is  not  always  in  the  same  direction ;  each  carbon 
is  alternately  positive  and  negative,  and  they  are  consumed  with 

'     Describe  the  machine  of  Nollet  and  Van  Malderen. 


488  HOLMES*  ' 

nearly  equal  rapidity :  for  the  production  of  the  electric  light, 
it  is  not  necessary  that  the  current  should  be  uniformly  in  the 
same  direction  ;  when  used  for  electro-metallurgy,  however,  this 
is  absolutely  requisite.  A  machine  of  four  wheels  gives  a 
light  equal  to  1 50  Carcel  lamps ;  a  machine  of  six  wheels,  a 
light  equal  to  200  Carcel  Inrrm^. 

470.  Holmes'  Magneto-Electric  Machine  for  use  in  Light- 
houses. Mr.  Holmes  has  succeeded,  by  the  use  of  a  powerful 
magneto-electric  machine,  in  producing  a  light  of  great  power 
and  intensity,  for  use  in  Light-houses.  The  general  arrange- 
ment of  the  machine  is  the  same  as  in  that  which  has  just  been 
described.  It  consists  of  48  pairs  of  permanent  compound 
bar-magnets,  arranged  in  six  parallel  planes,  so  as  to  form  a 
large  compound  wheel,  between  which  the  armatures,  160  in 
number,  are  arranged  in  five  sets,  the  tota!  amount  of  wire 
with  which  they  are  wound  being  about  half  a  mile  in*  length. 
The  wires  are  insulated  by  cotton,  and  are  so  arranged  as 
to  maintain  a  continuous  current  in  the  same  direction,  vary- 
ing from  a  maximum  to  exactly  one-half  the  amount  of  the 
maximum,  in  rapid  succession.  To  facilitate  the  change  in  the 
poles,  the  soft  iron  cores  of  the  coils  are  not  solid  pieces  of  iron, 
but  are  tubes,  single,  double  or  treble,  as  it  is  found  by  experi- 
ment that  the  same  weight  of  iron,  when  divided  in  this  man- 
ner, loses  or  takes  magnetism  in  much  less  time  than  when  in 
a  solid  form.  The  steel  bars  weigh  about  one  ton,  and  the 
wheel  is  made  to  revolve  by  a  steam  engine  of  one  or  two 
horse-power,  at  the  rate  of  150  to  250  times  per  minute.  There 
is  a  limit  to  the  velocity  to  be  employed  when  the  maximum  of 
electricity  is  required.  This  light  was  for  several  months  in 
successful  operation  at  the  South  Foreland  Lrght-house,  on  the 
English  Channel,  and  afterwards  at  Dungene  s,  the  actual  ex- 
pense of  fuel  in  working  the  steam  engine,  being  about  the  same 
as  that  of  the  oil  formerly  employed,  and  the  light  equal,  pho- 
tometrically, to  14  of  Fresnel's  first-class  Light-house  lamps. 
The  same  light  is  also  used  in  the  noble  Light-houses  of  La 
Here,  near  Havre.  This  light  is  nothing  but  the  sparks  first  ob- 
tained from  the  magnet  by  Mr.  Faraday,  Fig.  220,  made  continu- 
ous by  suitable  machinery.  It  is  said  to  possess  extraordinary 
penetrative  power  for  fogs,  and  that  it  shines  so  far  at  times,  that 
even  before  it  has  arisen  above  the  horizon,  twenty -five  miles 
off,  it  can  be  seen.  This  is  jusjly  regarded  as  one  of  the  most 

Describe  Holmes'  machine.  What  is  the  Telocity  of  revolution  ?  In  what  Light- 
housed  has  it  been  employed ?  How  far  can  it  be  seen ? 


MACHINE.  489 

interesting  scientific  applications  of  modern  times,  and  with  the 
additional  improvements  which  are  steadily  making,  will  no 
doubt  in  time  be  adopted  in  all  the  most  important  Light- 
houses throughout  the  world.  On  the  whole,  however,  up  to 
this  time,  the  preponderance  of  opinion  is  against  the  general 
introduction  of  magneto-electric  machines  into  Light-hou-es,  on 
account  of  their  liability  to  get  out  of  order,  and  the  difficulty 
of  securing  the  skilled  labor  required  for  their  efficient  man  ige- 
nrjnt,  there  being,  in  the  opinion  of  the  Brethren  of  the  Trinity 
House, — the  English  Light-house  Board, — no  advantages  which 
can  compensate  for  the  want  of  certainty  in  Light-house  illu- 
mination. In  spite  of  all  the  care  which  the  importance  of 
the  subject  has  rendered  necessary,  tli3  Dungeness  electric 
Light  entirely  failed,  or  was  inefficient,  for  upwards  of  119.^- 
hours,  between  Aug.  1863,  and  (X-t.  1864;  and  referring  to  this, 
th o  Brethren  of  the  Trinity  Hou^e  say  that  it  appears  to  them 
to  be  impossible  to  obtain  entire  immunity  from  such  accidents, 
so  long  as  human  nature  is  subject  to  infirmity.  These  fallings 
off  and  cessations  have  frequently  rendered  it  necessary  that 
the  ordinary  oil  Lamp  should  be  re-lighted ;  and  notwithstand- 
ing the  power  of  the  magneto-electric  light,  instances  have 
occurred  of  vessels  being  stranded  near  Dungeness.  The  ex- 
pense of  maintaining  an  equal  light  from  Colza  oil,  under  the 
old  oil-system,  from  wax-candles,  Bunsen's  battery,  and  the 
magneto-electric  machine,  being  about  the  same,  the  question 
must  be  decided  upon  grounds  of  convenience  and  effi  iency 
alone.  The  expenditure  of  a  Light-house  of  the  first-class  is 
about  £400  per  annum,  the  light  burning  four  thousand  hours, 
at  an  expense  of  about  two  shillings  per  hour. 

471.  Wilde's  Magneto-Electric  Machine.  A  great  im- 
provement has  recently  been  made  upon  Holmes'  machine  by 
the  substitution  of  powerful  electro-magnets,  in  place  of  perma- 
nent steel  magnets.  It  consists  in  the  application  of  the  current 
from  a  common  magneto-electric  machine,  produced  by  the  revo- 
lution of  coils  before  the  poles  of  a  series  of  small  permanent 
magnets,  to  the  formation  of  a  powerful  electro -magnet.  This 
is  done  by  causing  the  current  generated  by  the  revolution  of  the 
coils  to  circulate  through  wires  wound  in  the  ordinary  manner 
around  a  piece  of  soft  iron,  so  as  to  convert  it  into  a  powerful 
horse-shoe  eJectro-mngnet.  This  electro-magnet  possesses  much 
more  power  than  the  original  permanent  magnets,  on  account 

What  are  the  objections  to  their  u.«e  ?     What  is  the  comparative  expense  of  the  differ- 
ent modes  of  Ligiit-iiouse  illumination  ? — ill.  State  the  principle  of  Wilde's  machine. 


490  WILDE'S 

-  of  the  intensity  of  the  induced  current,  produced  by  the  revo- 
lution of  the  first  pair  of  coils.  In  front  of  the  poles  of  the 
.  electro-magnet  thus  formed,  a  second  pair  of  coils  is  made  to 
revolve  with  great  rapidity,  and  a  second  induced  current  of 
still  greater  intensity  than  the  first  is  obtained.  This  second 
induced  current  is  then  carried  around  a  second  horse-shoe  of 
soft  iron  and  a  second  electro-magnet  formed,  of  still  greater 
power  than  the  first.  In  front  of  the  poles  of  this  second 
electro-magnet,  a  third  pair  of  coils  is  made  to  revolve,  and 
a  third  induced  electrical  currrent  of  still  greater  power  than 
the  preceding  is  obtained.  Each  electro-magnet  and  each  in- 
duced current  being  more  powerful  than  those  which  precede 
them,  there  is,  theoretically,  no  limit  to  the  power  which  may 
l,e  thus  induced.  A  small  and  weak  permanent  magnet  may 
thus  be  made  to  actuate  a  series  of  electro-magnets  of  con- 
tinually increasing  power.  Wilde's  machine  is  constructed  on 
this  principle,  Fig.  250.  An  armature  s  A,  wound  with  insu- 
lated wire,  is  made  to  revolve  with  great  rapidity  by  means  of 
a  band  from  a  steam-engine  B,  in  front  of  the  poles  of  six  per- 
manent magnets,  M  M,  each  weighing  one  pound :  from  this 
armature  the  current  is  transmitted  by  the  wires  p  n,  through 
the  cups  c  c,  to  an  inverted  electro-magnet  E  M,  in  front  of 
whose  poles  a  second  armature,  carrying  coils,  is  made  to  re- 
volve by  means  of  a  band  B  p,  from  the  same  steam  engine : 
from  this  second  armature  the  current  which  is  produced  by  its 
revolution  is  carried  by  the  wires  p'  ri,  to  a  second  electro-mag- 
net, not  seen  in  the  Fig.,  in  front  of  who  e  poles  a  third 
armature,  carrying  coils,  is  made  to  revolve  by  means  of  the 
same  steam-engine,  and  from  these  coils  the  induced  current  is 
carried  by  wires  to  the  carbon  points  of  a  Duboscq's  electric 
lamp,  as  in  Fig.  249.  The  armatures  employed  in  this  machine 
are  not  wound  or  mounted  in  the  ordinary  manner,  but  according 
to  the  method  of  Siemen.  A  cylindrical  piece  of  iron  whose 
opposite  sides  are  cut  away,  represented  in  a  side  view  at  G,  No. 
1,  Fig.  251,  and  in  an  end  view  at  E,  is  wound  from  end  to  end, 
on  each  side  with  covered  wire,  until  the  grooves  on  both  sides  of 
the  cylinder  are  completely  filled :  these  longitudinal  coils  are 
then  firmly  bound  with  bands  of  brass  H  H,  No.  2,  Fig.  251,  that 
they  m;iy  not  be  displaced  by  the  centrifugal  force  of  the'  revolv- 
ing cylinder:  K  is  the  wheel  for  the  application  of  the  band  from 
thii  steam-engine  :  1 1  are  axles ;  L  L  is  the  pole-changer.  The 

How  is  the  current  induced  by  the  permanent  magnet  made  to  create  an  electro-mag- 
ne*  of  much  greater  power,  and  this,  one  of  still  gi eater  power,  and  this  a  third ?  Is 
tuere  any  limit  to  this  process  theoretically  ? 


491 


Wilde* s  Magneto-Electric  Machine. 

Fig.  251. 
1 


Sifmen's  Armature. 


T)<-<rrihe  the  construction  of  iVUJe's  machine      Whose' armature  is  employed?     How 
i*it  wouad? 


492  MACHINE, 

armature  thus  arranged  is  then  inserted  into  a  cylindrical  hole 
cut  to  receive  it  lengthwise  through  the  pieces  of  iron  c,  c,  which 
are  firmly  bolted  to  the  lower  ends  of  the  inverted  magnet  E  M, 
E  M.  These  pieces  of  iron  constitute,  therefore,  the  true  poles  of 
the  electro-magnet,  and  are  separated  from  each  other  by  pieces 
of  brass.  The  cylindrical  aperture  is  about  l-20th  of  an  inch 
larger  than  the  wound  armature,  so  that  it  may  revolve  in  very 
close  proximity  to  the  interior  of  the  hollow  cylinder  without 
touching  it.  The  armature  is  supported  at  each  end  by  appro- 
priate brass  supports,  and  revolves  with  great  accuracy.  It  is 
represented  in  place  at  s  A,  Fig.  250,  and  its  opposite  extrem- 
ity, to  which  the  band  from  the  steam-engine  is  attached,  at  p. 
It  is  shown  in  transverse  section,  with  the  extremities  of  the 
covered  wires,  in  Fig.  252,  where  b  b,  are  the  pieces  of  iron 

bolted  to  the  lower  extremities 
Fig-  252.  of  the  electro-magnet,    and  c  c, 

the  brass  pieces  by  which  they 
are  separated.  It  is  evident 
that  by  the  rapid  revolution  of 
this  cylinder  the  longitudinal 
coils,  are  continually  brought 
near  and  removed  from  the  poles 
of  the  electro-magnet  E  M,  E  M. 
The  opposite  electric  currents 
thus  induced  are  carried  by  the 
Tke  Armature  in  its  Socket.  wires  to  the  pole-changer  ar- 

ranged upon  the  axis  at  L  L', 

Fig.  251,  and  at  s  A,  Fig.  250,  and  there  converted  in  the 
ordinary  manner  into  permanent  currents  in  one  direction, 
whence  they  are  transmitted  to  a  second  electro-magnet,  or  di- 
rectly to  the  electric  lamp.  The  upper  armature  s  A,  revolving 
between  the  poles  of  the  permanent  magnets  MM,  is  arranged 
upon  the  same  plan.  In  Wilde's  largest  instrument  there  is  one 
set  of  permanent  magnets,  and  two  electro-magnets :  its  primary 
magneto-electric  machine  has  a  cylindrical  armature  of  1§ 
inches  diameter,  actuated  by  six  small  permanent  magnets 
weighing  one  pound  each:  the  induced  current  from  this  arma- 
ture is  transmitted  through  the  coils  of  an  electro-magnet  hav'ng 
a  cylindrical  armature  of  5  inches  diameter ;  and  the  induced 
current  from  this  is  finally  carried  to  the  coils  of  an  electro- 
magnet having  an  armature  of  10  inches  in  diameter:  the 

How  is  the  armature  mounted?    Describe  the  arrangement  of  Wilde's  instrument 
of  the  largest  size.     How  is  tie  intensity  armature  wouud?    The  (iuaiiti.y  armature  ? 


AND    ITS  493 

weight  of  the  la^t  ten-inch  electro-magnet  is  nearly  three  tons, 
and  the  total  \veight  of  the  instrument  about  four  and  half  tons. 
The  machine  is  provided  with  two  armatures,  one  for  intensity, 
the  other  for  quantity,  p,  429,  which  may  be  used  at  pleasure 
by  taking  out  one  and  introducing  the  other.  The  intensity 
armature  is  wound  with  a  comparatively  long  and  fine  covered 
wire,  376  feet  in  length,  and  weighing  232  Ibs.  The  quantity 
armature  is  wound  with  covered  copper  ribbon  67  feet  in  length, 
the  weight  of  which  is  344  Ibs.  With  the  three  armatures 
driven  at  a  uniform  velocity  of  1,500  revolutions  per  minute  by 
a  steam  engine  of  about  seven  horse-power,  an  amount  of  mag- 
netic force  is  developed  in  the  large  electro-magnet  far  exceed- 
ing any  thing  which  has  hitherto  been  produced,  and  an  amount 
of  induced  electricity,  when  the  ten-inch  quantity  armature  is 
employed,  so  enormous  as  to  melt  pieces  of  cylindrical  iron  rod 
fifteen  inches  in  length  and  fully  one-quarter  of  an  inch  in  di- 
ameter, and  pieces  of  copper  wire  of  the  same  length  and  one- 
eighth  of  an  inch  in  diameter.  With  this  armature  in  place, 
notwithstanding  its  tremendous  heating  power,  the  physiologi- 
cal effects  of  the  current  can  be  borne  without  inconvenience: 
immediately  after  fifteen  inches  of  iron  rod  have  been  melted 
the  terminals  may  be  grasped,  one  in  each  hand,  and  the  full 
force  of  the  currrent  sustained ;  the  shocks  are  severe,  but 
yet  not  inconveniently  so.  When  an  intensity  armature  seven 
inches  in  diameter  was  employed  in  another  machine,  consisting 
of  one  permanent  and  one  electro-magnet,  and  driven  at  a 
speed  of  1,800  revolutions  a  minute,  the  current  melted  seven 
feet  of  No.  16  iron  wire,  and  heated  a  length  of  twenty-one 
feet  of  the  same  wire  red-hot.  The  illuminating  power  of  such 
a  current  is  of  the  most  splendid  description.  When  an  electric 
lamp,  furnished  with  rods  of  gas-carbon  half  an  inch  square, 
was  placed  at  the  top  of  a  lofty  building,  an  arc  of  flame  several 
inches  in  length  was  projected,  and  the  light  evolved  from  it 
was  sufficient  to  cast  the  shadows  of  the  street  lamps  a  quarter 
of  a  mile  distant  upon  the  neighboring  walls.  When  viewed 
from  that  distance,  the  rays  proceeding  from  the  reflector  have 
all  the  rich  effulgence  of  sunshine.  With  the  reflector  removed 
from  the  lamp,  the  bare  light  is  estimated  to  have  an  intensity 
equal  to  4,000  wax  candles.  A  piece  of  ordinary  sensitive 
paper,  like  that  used  for  photographic  printing,  exposed  to  the 
action  of  the  light  for  20  seconds,  at  the  distance  of  two  feet 

Describe  th«  henting  effects  of  this  machine.     When  the  quantity  armature  Is  em- 
plo.,  ed  ,  whea  the  iateusit.,  armature,    ltd  physiological  effects.    Its  illurnkuting  effects. 


494  EFFECTS. 

from  the  reflector,  was  darkened  to  the  same  degree  as  a  piece 
of  the  same  sheet  of  paper  when  exposed  for  the  period  of  one 
minute  to  the  direct  rays  of  the  sun,  at  noon,  on  a  clear  day  in 
the  month  of  March.  In  the  month  of  June,  from  a  comparison 
of  sunlight  with  the  electric  light  armed  with  the  reflector, 
by  means  of  the  shadows  thrown  by  both  from  the  same 
object,  the  electric  light  seemed  to  possess  three  or  four  times 
the  power  of  sunlight.  That  the  relative  intensity  was  some- 
what in  this  proportion,  was  evident  from  the  powerful  scorch- 
ing action  of  the  electric  light  upon  the  face,  and  the  ease  with 
which  paper  could  be  set  on  fire  with  a  burning  glass  when 
introduced  into  its  rays.  The  extraordinary  caWific  and  illu- 
minating powers  of  the  ten-inch  machine  are  the  more  remark- 
able, when  we  consider  that  they  have  their  origin  in  six  small 
permanent  magnets,  weighing  only  one  pound  each,  and  only 
capable  of  sustaining  collectively  a  weight  of  sixty  pounds. 
It  has  been  calculated  that  with  a  100-ton  magnet,  having  an 
armature  of  32  inches  in  diameter,  and  driven  by  a  1,000  horse- 
power steam-engine,  light  enough  would  be  produced,  if  the 
lamp  were  placed  upon  the  top  of  a  high  tower,  to  illuminate 
London  by  night,  more  brightly  than  the  sunlight  does  by  day. 
Twelve  machines  of  the  ordinary  size  would  illuminate  Broad- 
way, from  the  Battery  to  Fourteenth  St.,  at  much  less  expense 
than  gas. 

One  great  advantage  of  this  machine  is  its  capability  of  en- 
largement to  any  required  power.  If,  instead  of  using  the 
current  from  the  ten-inch  armature  of  the  second  electro-magnet 
for  the  production  of  light,  it  were  to  be  used  in  producing  a 
still  larger  electro-magnet,  a  vastly  greater  development  of 
power  would  be  the  result.  The  only  apparent  limit  to  this 
multiplication  of  power  is  the  excessive  heat  which  would  be 
developed  in  the  rotating  armatures:  this  might,  perhaps,  be 
pushed  so  far  as  to  burn  up  all  the  working  parts,  dissipate  the 
electric  lamp  and  conducting  wires,  destroy  the  attendants,  and 
become  in  fact  perfectly  unmanageable. 

A  practical  application  of  this  Light  has  been  made  to  Pho- 
tography :  an  establishment  has  been  fitted  up  at  Manchester,  in 
England,  with  one  of  these  machines,  by  which  more  than  two 
hundred  negatives  can  be  taken  in  one  day.  Its  constancy  ren- 
ders it  more  reliable  than  an  uncertain  sunlight.*  The  ordinary 
consumption  of  coal  required  to  work  a  7  horse-power  steam- 
How  does  the  light  compare  with  sunlight  ?  What  is  its  effect  on  photographic  pa- 
per? What  effect  would  probably  be  produced  by  an  armature  of  32  inches?  Is  there 
•any  limit  to  this  multiplication  of  power?  What  practical  application  has  been  mad* 


IMPROVEMENTS  495 

engine,  midway  between  waste,  on  the  one  hand  and  rigid 
economy  on  the  other,  is  about  11^  Ibs.  per  hour,  worth  about 
one  half-penny.  To  this  expense  must  be  added  that  of  the 
carbon  rods  for  the  lamp,  about  ten  inches  per  hour,  worth  per- 
haps an  English  penny,  then  interest  on  the  cost  of  the  machine, 
expense  of  maintenance  and  repairs,  which  will  bring  up  the 
total  expense  per  hour,  of  this  enormous  quantity  of  Liglit, 
not  less  than  4,000  wax  candles,  to  six-pence  or  eight-pence. 
The  British  Commissioners  of  Northern  Light-houses  have 
ordered  one  of  Wilde's  machines,  at  a  cost  of  £500. 

469.*  Improvements  on  Wilde's  Machine.  Various  im- 
provements have  been  made  upon  Wilde's  machine,  founded 
upon  the  fact  that  an  electric  spark  can  be  obtained  from  the 
coils  of  an  electro  magnet,  which  has  been  powerfully  excited, 
for  some  time,  (in  one  case  more  than  25  seconds,)  after  the 
exciting  battery  current,  or  magneto-electric  current,  has  heen 
discontinued.  An  electro-magnet  possesses  the  power  of  in- 
ducing a  charge  of  electricity  in  its  coils,  and  retaining  it,  in  a 
manner  analogous  to  th-it  in  which  it  is  retained,  in  insulated 
sub-marine  cables,  §416,  and  in  the  Leyden  jar,  but  arising 
from  a  different  cause,  and  it  is  this  induced  charge  of  elec- 
tricity, which  produces  the  spark  observed  at  the  point  of  dis- 
junction of  the  insulated  wires  of  an  electro-magnet,  a  consider- 
able time  after  all  connection  with  the  original  exciting  bat- 
tery current,  has  been  cut  off.  The  induction  of  this  electric 
charge  is  due  to  the  retention  of  a  considerable  degree  of  mag- 
netic power  by  the  iron  core  of  the  electro-magnet,  and  to  the 
comparatively  slow  manner  in  which  large  masses  of  iron 
lose  their  magnetism  and  return  to  their  normal  condition 
after  having  been  very  highly  excited.  It  is  this  important 
retentive  power  of  the  iron  core  of  the  electro-magnet  E  M, 
which  in  the  case  of  Wilde's  machine,  Fig.  250,  keeps  up  a 
steady  flow  of  induced  electricity  in  the  coils  of  its  armature  s  A, 
notwithstanding  the  intermittent  character  of  the  electric  cur- 
rent generated  in  the  revolving  coils  of  the  armature  of  the 
permanent  magnets  M  M,  for,  as  is  well  known,  no  current  what- 
ever proceeds  from  the  armature  of  the  magneto  electric  ma- 
chine, in  certain  positions  during  its  revolution.  Consequently 
the  electro  magnet  E  M,  in  Wilde's  machine,  retaining  its  mag- 
netic power,  having  been  once  excited,  for  some  time  after  the 
current  which  actuated  it  has  been  stopped,  is  capable  of 
exciting  a  current  in  its  revolving  armature  s  A,  without  any 
further  connection  with  the  armature  of  the  magnets  M  M. 


496  UPON  WILDE'S  MACHINE. 


Siemens'  and  Wheatstone's  Machines-  On  tills  prin- 
ciple a  modification  in  Wilde's  machine  was  made  soon  after  its 
invention  by  Siemens'  in  Germany,  and  by  Wheatstone  inde- 
pendently in  England.  In  Siemens'  machine  the  steel  magnets 
M  M,  Jfiff.  250,  are  replaced  by  an  electro  magnet,  which  is  ex- 
cited by  a  galvanic  battery,  the  armature  caused  to  rotate,  and 
then  the  battery  removed  :  or,  instead  of  employing  a  battery  the 
soft  iron  of  the  electro-magnet  is  slightly  magnetized  by  touching 
it  for  a  few  minutes  with  a  permanent  magnet.  The  residual 
magnetism,  left  in  the  soft  iron  of  the  electro  magnet,  after  being 
under  the  influence  of  the  battery,,  or  touched  by  the  permanent 
magnet,  is  abundantly  sufficient  to  induce  a  current  of  electricity, 
in  the  coils  of  its  rapidly  revolving  armature,  which  is  then  car- 
ried to  the  electro-magnet  E  M  and  used  to  actuate  it. 

In  Wheat-tone's  apparatus,  the  conducting  wires  from  the 
extremities  of  the  coils  of  the  armature  of  the  electro  magnet 
E  M,  divide  into  two  branches,  one  branch  leading  to  the  insu- 
lated wire  which  is  wound  around  a  small  primary  actuating 
electro  magnet  substituted  for  the  permanent  magnets  M  M, 
Fig.  250,  and  the  other  branch  leading  to  the  carbon  points 
of  the  electric  lamp.  In  this  manner  a  portion  of  the  electric 
current  induced  in  the  principal  electro-magnet  E  M  is  di- 
'  verted  to  the  primary  electro-magnet  thereby  greatly  increas- 
ing its  magnetic  power,  and  proportionately  augmenting  the 
electric  current  which  it  induces  in  its  coils  and  transmits 
to  the  .principal  electro-magnet,  while  the  remaining  portion  is 
4ra\vn  off  and  used  in  the  ordinar}'-  manner  for  the  production 
of  light,  effecting  decomposition,  and  the  like.  The  residual 
magnetism  of  the  primary  electro-magnet,  after  being  connected 
with  the  battery,  or  touched  by  the  permanent  magnet,  is  the 
original  cause  of  the  electric  current,  but  this  magnetism  is  imme- 
diately increased,  the  instant  the  armatures  begin  to  revolve,  by 
the  flow  of  a  portion  of  the  induced  current,  from  the  coils  of  the 
armature  of  the  secondary  electro-magnet  E  M,  through  the  insu- 
lated wires  with  which  the  primary  electro-magnet  is  wound  ; 
this  in  turn  augments  every  instant  the  force  of  the  secondary 
current,  which  at  once  reacts  again  upon  the  primary  current, 
and  so  the  induction  of  electricity  goes  on  with  continually 
augmenting  intensity,  limited  only  by  the  speed  of  the  arma- 
tures, the  strength  of  the  apparatus,  and  the  extreme  heat 
which  is  generated.  The  heat  produced  is  one  of  the  greatest 
obstacles  to  the  success  of  these  machines,  and  is  due  not  sim- 
ply to  the  heating  effect  of  powerful  currents  of  electricity,  but 


LADD'S 


497 


also  to  the  conversion  of  a  portion  of  the  motion  of  the  arma- 
tures into  heat,  according  to  the  mechanical  theory  of  heat, 
for  the  electro-magnets  exert  a  retarding  effect  upon  the  revolu- 
tions of  the  armatures,  the  more  their  power  is  augmented  the 
greater  this  retardation,  the  greater  the  resistance,  the  greater 
the  heat,  and  the  larger  the  amount  of  mechanical  power  nec- 
essary to  overcome  it.  This  is  the  reason  that  the  more 
powerful  the  electric  currents  induced,  the  greater  the  power 
which  is  required  to  produce  the  revolution  of  the  armatures. 
471.*  Ladd's  Improvement  upon  Wilde's  Machine.  Mr. 
Ladd,  a  philosophical  instrument  maker  of  London,  at  the  sug- 
gestion of  one  of  his  workmen,  by  the  name  of  Tisley,  has 
greatly  increased  these  effects,  by  discarding  altogether  the 
permanent  magnets  M  M  of  Wilde's  machine,  Fig.  250,  and  also 
the  primary  electro-magnet  actuated  by  the  battery,  of  Wheat- 
stone's  improvement,  and  by  making  use  of  the  residual  magnetism 
of  the  principal  electro-magnet  E  M,  as  explained  in  the  last 

Fig.  251.* 


r   i  > 


Ladd's  Improved  Wilde's  Machine 


498  FIRST    IMPROVEMENT. 

article,  to  start  the  electric  current  in  the  coils  of  its  revolving 
armature.  Instead  of  one  curved  electro -magnet,  two  straight 
electro-magnets  are  placed  in  a  horizontal  position  and  parallel 
to  each  other,  with  poles  reversed  and  having  one  revolving 
armature  between  each  set  of  poles.  The  electric  current  pro- 
duced by  the  coils  of  one  armature  is  used  to  increase  the  power 
of  the  electro-magnets,  while  that  from  the  coils  of  the  other  is 
carried  to  the  carbon  points  of  the  electric  lamp  and  is  used  for 
the  production  of  light.  The  apparatus  is  represented  in  Fig. 
251*.  B  B'  are  the  two  electro-magnets  corresponding  with  E  M 
in  Fig.  250,  and  placed  horizontally.  The  coils  are  connected 
on  the  right  so  as  to  form  but  one  circuit.  Two  armatures  are 
provided,  M  and  M',  one  at  each  end  of  the  electro  magnets  B  B'. 
The  wires  p  and  w,  from  one  armature  are  carried,  as  shown  in  the 
figure,  directly  to  the  electro-magnets  and  are  used  to  increase 
their  force.  The  wires  ^t/and  n'  from  the  other  armature  lead  to 
the  carbon  points  of  the  electric  light,  i,  as  in  Fig.  251,  or  may 
be  used  for  producing  any  of  the  other  effects  of  the  current, 
such  as  the  decomposition  of  water,  and  the  like.  It  is  inter- 
e.sting  to  observe  the  continuance  of  the  effects,  for  some  time 
after  the  cessation  of  the  revolutions,  as  is  shown  by  the  rise  of 
bubbles  of  gas  from  the  platinum  poles  of  the  decomposing  cell 
in  the  case  of  the  decomposition  of  water,  Fig.  162.  In  order 
to  carry  off  the  great  heat  which  is  produced,  when  the  revolu- 
tions are  exceedingly  rapid,  the  armatures  are  punctured  and 
a  stream  of  water  is  made  to  circulate  through  them  ;  by  this 
arrangement  they  are  kept  nearly  perfectly  cool. 

472.*  Ladd's  Second  Improvement.  A  subsequent  im- 
provement has  recently  been  introduced  in  «the  arrangement 
of  the  armatures.  Instead  of  being  placed,  as  before,  at  the  oppo- 
site extremities  of  two  electro-magnets,  as  in  Fig.  251,  they  are 
brought  together  end  to  end,  and  fastened  very  strongly,  so 
as  to  constitute  but  one  shaft,  revolving  in  one  cylindrical 
aperture,  mounted  between  the  poles  of  one  curved  electro- 
magnet, like  E  M  Fig.  250,  and  driven  by  one  band.  The  coils 
wound  upon  one  armature  of  the  shaft  are  used  to  actuate  the 
electro-magnet,  and  increase  its  power;  the  coils  of  the  other 
armature  are  used  to  produce  the  electric  light,  or  for  any 
other  external  work.  The  coils  upon  the  two  armatures  are  not 
placed  upon  a  line  with  each  other,  but  at  right  angles,  so  that 
one  is  exerting  its  utmost  power,  at  the  moment  when  the  other 
is  at  its  dead  point ;  or  they  maybe  adjusted  at  any  other  angle 
which  experience  proves  to  be  productive  of  the  most  powerful 


LADD'S 


499 


effects.     By  this  arrangement  the  construction  of  the  appara- 
tus is  greatly  simplified.     The  machine  is  represented  in  Fig. 
252*.    It  will  be  observed  that  the  permanent  magnets  M  M  have 
Fig.  252*. 


LadtPs  Second  Improvement. 

been  discarded  and  that  there  is  no  primary  electro-magnet  ac- 
tuated by  a  battery,  but  simply  the  principal  electro-magnet  K  M 
of  Wilde's  machine,  and  on  the  top  of  it,  a  shaft  arranged  with  a 
crank  and  wheels  for  the  purpose  of  imparting  motion  to  the 
revolving  Siemens'  armature  placed  below.  This  armature  is 
provided  with  two  entirely  distinct  sets  of  coils  insulated  from 
each  other.  The  terminal  wires  of  one  set,  p  and  n,  are  car- 
ried to  the  electro-magnet,  and  their  current  is  used  to  exalt  its 
powfr.  The  terminal  wires  of  the  other  set,  pr  and  nf,  corres- 
pond with  the  terminal  wires  of  Wilde's  machine,  Fig.  25",  and 
their  current  is  used  to  produce  the  electric  light,  or  for  any 
other  external  work.  These  two  sets  of  coils  operate  entirely 
independent  of  each  other.  The  instant  the  armature  is  made 
to  revolve  by  turning  the  crank  of  the  machine,  a  f -eble  cur- 
rent of  electricity  is  generated  in  the  coils  by  the  slight  amount 


500  SECOND  IMPROVEMENT. 

of  magnetism  retained  by  the  electro-magnet  since  its  previous 
excitation.  If  it  should  have  entirely  lost  its  magnetism  this 
may  be  restored  for  the  occasion  by  applying  a  powerful  per- 
manent steel  magnet  to  the  poles  of  the  electro-magnet,  or  by 
touching  these  poles  for  a  moment  by  a  movable  electro-mag- 
net actuated  for  the  time  by  a  small  battery.  To  this  induced 
magnetism  the  current  from  that  set  of  coils  which  is  directly 
connected  with  the  electro-magnet  of  the  machine  immediately 
adds  its  magnetic  power  and  at  the  next  revolution  of  the  arma- 
ture the  current  of  electricity  in  both  coils  is  greatly  iucreased : 
this  in  turn  adds  to  the  magnetic  force  of  the  electro-magnet, 
which  at  once  reacts  again  upon  the  coils,  and  so  the  process 
goes  on  as  the  rapidity  of  revolution  increases.  There  is  no 
limit  to  the  power  of  the  machine  but  the  rapidity  with  which 
the  armature  is  made  to  rotate,  and  this  is  entirely  dependent 
upon  the  amount  of  mechanical  force  derived  from  the  steam- 
engine.  The  great  improvement  in  this  machine  is  the  intro- 
duction of  the  second  coil  upon  the  Siemens'  ai  mature,  which, 
although  it  gives  off  currents  induced  by  tHe  electro-magnet, 
does  not  at  all  detract  from  the  intensity  of  the  original  coil ; 
and  when  the  former  is  attached  to  a  Duboscq's  lamp,  it  is  found 
to  give  a  light  equal  to  40  elements  of  Grove  and  Bunsen, 
from  the  expenditure  of  an  amount  of  steam  engine  force  equiva- 
lent to  one  horse-power.  One  of  these  machines,  at  the  Paris 
Exhibition  of  1867,  24  inches  in  length,  12  in  width,  and  7 
inches  high,  kept  50  inches  of  platinum  wire  1-1  Oth  of  an  inch 
in  diameter,  incandescent,  and  when  a  small  voltameter  was 
placed  in  the  circuit  of  the  double  armature,  gave  off  about  16 
cubic  inches  of  gas  per  minute,  and  in  connection  with  an  electric 
lamp,  emitted  a  light  equal  to  that  of  about  thirty-five  Grove's 
elements,  the  driving  force  being  less  than  one  horse-power. 

These  electro-magnetic  machines  are  all  extremely  interest- 
ing as  illustrations  of  the  theory  of  the  Convertibility  of  Forces. 

473.  Points  of  difference  between  the  electricity  of  the 
Electrical  Machine  and  that  of  the  Galvanic  Battery.  We 
have  already  noticed,  §351,  some  of  the  points  of  difference 
between  the  electricity  of  the  machine  and  that  of  the  battery, 
viz :  that  the  electricity  of  the  machine  possesses  great  inten- 
sity, but  limited  quantity  ;  that  of  the  battery,  feable  intensity, 
but  large  quantity,  that  its  influence  upon  electrometers  and 
electroscopes,  is  extremely  slight,  that  a  Leyden  jar  can  only  be 
charged  with  difficulty,  that  when  the  polar  wires  are  brought 

470.*  Describe  Siemens'  and  Wheatstone's  machines. — 471.*-472.*  Ladd's  machines. 


THE    ELECTRICITY    OF    THE    MACHINE  501 

near  each  oilier  only  a  feeble  spark  will  pass,  and  on  establish- 
ing a  communication  between  them  by  means  of  the  hands,  pre- 
viously moistened,  a  shock  is  felt,  but  only  for  a  moment:  we 
have  also  seen,  §415,  that  its  velocity  is  very  much  less,  prob- 
ably not  exceeding  18,000  miles  per  second,  while  the  velocity 
of  statical  electricity  is  288,000  miles  per  second.  On  thw 
other  hand,  galvanic  electricity  is  developed  in  much  larger 
quantity  than  statical,  and  in  a  steadily  flowing  current ;  it  pos- 
sesses also  much  greater  heating,  chemical  and  magnetic  power, 
and  exerts  a  peculiar  effect  upon  the  nervous  system  of  animals. 
Notwithstanding  these  points  of  difference,  it  was  believed  from 
the  earliest  period  in  the  history  of  galvanism,  that  it  could  bi> 
identified  with  statical  electricity,  and  many  attempts  were  made 
to  establish  the  most  conclusive  test  of  identity,  viz  :  the  projec- 
tion of  the  electric  spark  between  the  poles  before  actual  c  in- 
tact, corresponding  with  the  escape  of  vivid  sparks  from  the 
h  ghly  excited  prime  conductor  of  an  electrical  machine.  The 
electricity  which  is  excited  by  rubbing  a  glass  tube  with  a  silk 
handkerchief,  will  pass  without  difficulty  across  half  an  inch 
of  space,  and  give  a  bright  and  noisy  spark,  while  the  electri- 
cal current  of  a  battery  of  several  hundred  pairs,  will  hardly 
force  a  passage  through  a  stratum  of  air  too  thin  to  be  appre- 
ciated, or  produce  a  spark  bright  enough  to  be  perceptib'e. 
Sir  H.  Davy  asserted  that  2,000  pairs  of  Wollaston  plates,  the 
most  perfect  form  of  the  battery  in  his  day,  gave  a  spark  l-20th 
to  l-40th  of  an  inch  in  air,  and  ^  an  inch  in  vacua.  Mr.  Chil- 
dren stated  that  1,250  pairs  gave  sparks  through  l-50th  of  an 
inch.  Daniell  asserted  that  he  had  often  seen  sparks  playing 
between  the  cells  of  his  battery  when  they  were  approximated 
too  much.  Faraday  stated  that  a  spark  would  pass  before  contact 
even  with  a  single  pair.  On  the  the  other  hand,  many  experi- 
menters were  inclined  to  deny  the  passage  of  any  electrical  spark 
at  all  before  contact,  even  with  the  most  powerful  batteries. 
Jacoby  found  that  the  current  from  12  pairs  of  plates  in 
the  most  active  operation,  would  not  pass  through  l-20,000th 
of  an  inch.  Gassiot  asserted  that  a  battery  of  loO  pairs  would 
not  project  a  spark  through  1 -5,000th  of  an  inch  before  contact, 
though  it  would  give  a  minute  but  not  brilliant  spark  on  sepa- 
rating the  poles,  if  tipped  with  charcoal:  also,  that  a  water  bat- 
tery of  1,024  pairs,  would  not  project  a  spark  through  l-5,00()ih 

VThat  is  the  influence  of  galvanic  electricity  upon  electrometers  and  the  T.eydenjar? 
What  is  the  power  of  giving  shocks  an'i  sparks?  What  is  its  velocity?  How  was  the 
identity  of  the  two  attempted  to  be  proved?  Give  the  statements  of  Davy,  Children, 
Daniell,  Faraday,  Jacoby  and  Gassiot,  in  regard  to  the  projection  of  sparks  by  the  battery. 


502  AND    BATTERY    COMPARED. 

of  an  inch,  although  a  Leyden  battery  could  be  charged  by  it, 
so  as  to  project  a  stjark  through  6-5,OOOths  of  an  inch.  Walker 
proved  that  a  constant  battery  of  99  cells  would  not  project  the 
spark  through  the  thinnest  measurable  stratum  of  air.  But  it 
was  finally  determined  by  Crosse,  in  1840,  that  a  water-battery 
of  1,200  pairs,  would  give  a  constant  small  stream  of  sparks 
between  the  polar  wires  l-100th  of  an  inch  apart,  before  contact  ; 
and  Gassiot,  suspecting  that  his  previous  battery  series  had  not 
been  sufficiently  extended  or  insulated,  constructed  a  water- 
battery  of  3,000  pairs,  and  obtained  sparks  freely  from  its  pole-. 
By  these  experiments  it  came  to.be  definitely  settled  that  the 
galvanic  battery  would  project  a  spark  like  a  common  electrical 
machine,  and  an  actual  identity  was  established  .  between  gal- 
vanic and  statical  electricity. 

471.  Points  of  resemblance  between  the  Electricity  of 
the  Electrical  machine  and  the  secondary  currents  of  Electri- 
city induced  by  the  primary  current  of  the  Battery  and  by 
Mag-nets.  On  the  other  hand,  the  secondary  current  of  ele  •- 
tricity  induced  by  the  primary  current  of  the  battery,  on  mak- 
ing and  breaking  connection,  not  being  derived  from  the  bat- 
tery or  from  the  primary  current,  but  being  simply  the  natural 
electricity  of  the  secondary  wire,  disturbed  and  brought  into 
activity  by  inductive  influence,  might  be  expected  to  exhibit  a 
very  close  resemblance  to  that  of  the  electrical  machine,  which 
is  also  nothing  but  the  natural  electricity  of  the  glass  plate  of 
the  machine  thrown  into  a  state  of  disturbance  by  means  of 
friction.  Thus,  by  the  magneto-electric  machine,  the  gold 
e:ive$  of  the  electroscope  may  be  made  to  diverge  directly 
without  the  aid  of  a  condenser,  and  a  Leyden  jar  may  be 
charged  at  every  touch,  provided  one  terminal  wire  of  the  coll 
is  in  connection  with  the  outer  coating  of  the  jar,  and  the  other 
carried  to  the  knob  by  an  insulated  handle,  the  knob  being 
connected  with  the  inner  coating  by  a  wire  instead  of  a  chain  : 
the  sparks  which  are  emitted  are  of  the  most  vivid  character, 
of  great  power,  and  violence,  and  often  times  extend  through  a 
space  of  several  inches,  surpassing  all  electrical  machines  except 
those  of  the  largest  size  :  the  shocks  are  al  o  extremely  violent, 
and  frequently  danfrerous,  and  the  noise  almost  deafening. 

475.  The  quantity  of  Electricity  produced  by  the  Battery 
immense,  and  its  magnetic  effect  far  superior  to  that  of  the 
Machine.  Notwithstanding  the  extremely  feeble  intensity  'of 


Give  the  experiment  of  Crosse,  and  the  second  experiment  of  Gassiot.  What 
present  opinion  in  regard  to  their  identity  ?—  474.  State  the  points  of  resemblance  be- 
tween the  electricity  of  the  machine  aud  that  of  the  secondary  current  induced  by  the 
primary  current  and  by  magnets. 


THE    QUANTITY    OF    ELECTRICITY  503 

the  electricity  of  the  battery,  its  quantity  is  enormous.  Mr. 
Faraday  estimated  the  quantity  of  electricity  furnished  by  the 
decomposit'on  of  a  single  grain  of  water,  as  equal  to  eight  hun- 
dred thousand  discharges  of  a  battery  of  Leyden  jars  exposing 
thirty-five  hundred  square  inches  of  surface,  and  charged  by 
thirty  turns  of  a  powerful  electrical  machine.  The  experiment 
was  performed  in  the  following  manner. — Two  wires,  one  of 
zinc  and  one  of  platinum,  each  l-18th  of  an  inch  in  diameter, 
were  immersed  during  4-30ths  of  a  second,  to  the  depth  of 
5-8ths  of  an  inch,  and  5-lCths  of  an  inch  apart,  in  acidulated 
water  prepared  by  adding  a  single  drop  of  sulphuric-  acid  to 
four  ounces  of  water.  The  current  produced  by  this  exceed- 
ingly small  battery,  effected  as  great  a  de via! ion  of  the  galvan- 
ometer needle,  and  decomposed  the  same  amount  of  iodide  of 
potassium,  as  thirty  turns  of  a  powerful  plate  electrical-machine: 
twenty-eight  turns  of  the  machine  produced  an  effect,  percepti- 
bly less  than  that  produced  by  the  two  wires.  The  quantity 
of  acidulated  water  decomposed  within  the  battery  in  order  to 
furnish  this  vast  amount  of  electricity,  was  so  small  as  to  be 
incapable  of  measurement,  and  entirely  inappreciable;  but  the 
electricity  produced  by  it,  if  concentrated  so  as  to  be  discharged 
in  a  single  flash  during  a  minute  fraction  of  a  second,  from  a 
Leyden  battery  having  3,500  square  inches  of  surface,  would 
kill  a  cat  or  a  rat,  and  be  intolerable  to  a  man.  From  this  ex- 
periment Mr.  Faraday  made  the  calculation  that  the  electricity 
produced  by  the  decomposition  of  a  single  grain  of  water  in  the 
battery  by  the  action  of  the  zinc  plate,  is  equal  to  that  fur- 
nished by  eight  hundred  thousand  discharges  of  an  electrical 
machine,  each  equal  to  the  one  just  described  :  or  that  the  de- 
composition of  one  grain  of  water  evolves  a  quantity  of  elec- 
tricity sufficient  to  charge  a  surface  of  400  acres,  an  amount 
hardly  exceeded  in  the  most  violent  storms.  It  has  been 
calculated,  that  if  this  amount  of  electricity,  furnished  by  one 
grain  of  water,  were  spread  upon  a  cloud  two-thirds  of  a 
mile  distant  from  the  earth,  it  would  exert  an  attractive  force 
upon  the  earth  beneath  it,  of  1,664  tons !  and  that  if  the  atoms 
of  oxygen  in  this  grain  of  water  were  attached  to  one  thread 
l-25th  of  an  inch  long,  and  those  of  h}d:ogen  to  another,  th<j 
force  required  to  separate  the  thread-)  in  one  second,  woulfc 
be  7/2-">0  tons!  yet  this  amount  of  electricity  is  evolved,  withou' 

475.  Describe  Mr.  Faraday's  experiments  upon  the  quantity  of  electricity  producf  ' 
by  the  buttery.     Give  his  conclusion  in  regird  to  the  amount  set  free  in  the  derompo.',. 
tion  of  -i  single  grain  of  water.     Describe  the  difference  betweeu  the  electricity  of  t'-1\ 
machine  and  that  of  the  battery  in  regard  to  magnetic  effect. 


504  PRODUCED    BY    THE    BATTERY    IMMENSE. 

noise,  shock,  or  visible  appearance  of  flame,  in  every  case 
when  rather  less  than  six  cubic  inches  of  hydrogen  and  three 
cubic  inches  of  oxygen,  are  set  free  by  the  action  of  four 
grains  of  zinc  upon  one  grain  of  water.  This,  if  concentrated 
into  a  single  discharge,  would  be  equal  to  a  very  vivid  flash 
of  lightning,  whence  it  follows  that  the  electricity  set  free  in 
the  decomposition  of  one  grain  of  water  by  the  four  grains 
of  zinc  which  are  required,  yields  an  amount  of  electricity 
equal  to  that  of  a  powerful  thunder-storm.  Such  is  the  differ- 
ence between  the  electricity  of  the  battery  and  the  e^ctricity 
of  the  machine,  in  regard  to  quantity.  Their  difference  in 
regard  to  magnetic  effect  is  equally  remarkable.  A  piece  of 
copper  and  a  piece  of  zinc,  the  size  of  a  cent,  will  produce  a 
magnetic -effect  far  superior  to  that  exerted  by  the  most  pow- 
erful discharge  of  the  electricity  of  the  machine  ever  obtained. 
In  experiments  made  upon  the  Atlantic  cable,  an  electric  cur- 
rent was  sent  through  one  thousand  miles  of  it  submerged  in 
the  water  and  a  sufficient  •  magnetic  effect  exerted  upon  the 
reflecting  galvanometer,  §418,  to  communicate  a  message,  by  a 
battery  consisting  of  a  silver  wire  and  a  zinc  wire  of  the  size  of 
a  pin,  excited  by  a  drop  of  acid  supported  between  them  by 
capillary  action. 

475.  The  action  of  Electricity  and  Magnetism  on  Lig-ht. 
Electricity,  whether  produced  by  the  machine,  by  the  battery, 
or  by  magnetism,  has  not  only  the  power  of  produc'ng  light, 
but  a'so  a  very  singular  effect  on  light  after  it  is  produced.  Sir 
H.  Davy  ascertained,  §359,  that  the  light  produced  by  the 
approach  of  two  poles  of  a  powerful  battery,  is  influenced  by  the 
magnet,  and  is  acted  upon  in  the  same  way  as  any  moveable 
m3tallic  conductor  traversed  by  the  galvanic  current:  it  is  at- 
tracted and  repelled  by  the  mug- 

Fig.  253.  Fig.  2r>4.  net,  and  a  rotary  motron  imparted 

manifesting  itself  by  a  change  in 
the  form  of  the  arc.  By  holding 
the  magnet  in  a  certain  position, 
the  flame  may  be  made  to  re- 
volve, accompanied  by  a  louJ 
sound ;  and  the  form  of  the  arc 
may  even  become  broken  by  too 
great  an  attraction  or  repul  ion. 
The  arc  of  Voltaic.  Light.  Fig.  253  represents  the  ordinary 

473     State  the  effect  of  the  magnet  on  the  electric  light.     How  has  it  been  shown 
that  light  is  strongly  diamaguetic  J 


THE    EFFECT    OF    MAGNETISM! 


5C5 


Fig.  255. 


form  of  the  voltaic  arc  between  two  cylinders  of  plumbago, 
and  Fig.  254  the  curved  form  which  it  exhibits  under  the  in- 
fluence of  a  magnetic  pole.  It  has  also  been  ascertained  that 
light  is  strongly  dia-magnetic,  and  assumes  an  equatorial  position 
in  the  magnetic  field.  Bancalari  observed  that  the  name  of  a 
candle  placed  between  the  poles  of  an  electro-magnet,  was  re- 
pelled into  a  position  at  right  angles  to  a  line  joining  the  poles, 
Fig.  255,  as  if  blown  by  a  current  of  air.  M.  Quet  obtained  a 

similar  result  by  submitting 
the  voltaic  arc  to  the  influence 
of  powerful  electro-magnetic 
poles,  Fig.  256.  It  has  been 
shown  that  the  auroral  light 
produced  by  Ruhmkorff's  coil 
in  the  electric  egg,  Fig.  234,  is 
made  to  revolve  around  an 
electro-magnet  as  eoon  as  the 
connection  is  formed  with  the 
battery,  tnat  the  stratified 
bands  and  luminous  discharges 
of  Geissler's  tubes,  §461,  are 
powerfully  affected  by  the 
magnet,  and  that  the  light 

from  the  negative  pole  is  specially  affected  by  the  magnetic 
force.  Finally  Mr.  Faraday  has  as<  ertained  that  a  ray  of  light 
may  be  electrified  and  the  electric  forces 
illuminated.,  He  observed  that  if  a  ray  of 
polarized  light  were  transmitted  through  a 
piece  of  glass  placed  between  the  poles  of  a 
powerful  electro-magnet,  on  the  line  joining 
the  two  poles,  on  actuating  the  electro-mngnet 
by  connection  with  the  battery,  the  ray  of 
polarized  light  experienced  a  rotation,  to  the 
right  or  the  left,  according  to  the  direction 
of  the  current.  A  polarized  ray  of  light 
is  one  which  by  reflection,  or  by  refraction 
through  certain  substances,  has  acquired  cer- 
tain peculiar  proper! ies  different  from  those 
of  ordinary  light,  which  are  summed  up  in 
the  term  polarization.  Thus,  when  a  ray  of 
light  falls  upon  a  glass  mirror  at  an  angle 


The  effect  of  a  powerful  El'c'ro- Magnet 
on  the  flame  of  a  Candle. 


Fig.  256. 


The   (ffert  of  Magnft- 
jsm  on  the  Voltaic  Light. 


What  is  the  effect  of  the  magnet  on  the  voltaic  arc?  on  the  aureraj  light  of  Ruhrn* 
korff's  coil  and  Geissler's  tubes?  What  is  the  effect  of  Maguetisru on  polarized  Light? 
"What  is  polarized  Light  ? 


506 


ON    LIGHT. 


of  35°  25',  it  acquires  the  singular  property  of  incapability 
of  reflection  from  a  second  mirror  of  glass  at  the  same  angle, 
if  the  plane  of  incidence  of  the  second  mirror  be  perpendic- 
ular to  the  plane  of  incidence  of  the  first :  in  other  words, 
the  ray  becomes  extinguished;  it  is  partially  reflected  and 
re-appears,  for  every  other  inclination  of  the  two  planes,  and 
the  intensity  of  the  ray  reflected  from  the  second  mirror  in- 
creases as  the  angle  of  the  two  planes  of  reflection  diminishes. 
If,  at  the  moment  of  extinction,  a  thin  plate  of  quartz  crystal, 
whose  faces  are  perpendicular  to  its  axis,  be  interposed  be- 
tween the  two  mirrors,  the  extinguished  ray  re-appears  upon 
the  second  mirror,  and  in  order  to  re-extinguish  it  the  quartz 
must  be  turned  by  a  certain  angle  to  the  right  or  the  left.  The 
quartz  is  said  to  exercise  thus  a  rotary  power,  and  to  deviate 
the  plane  of  polarization  to  the  right  or  to  the  left,  according 
to  the  direction  in  which  it  must  be  turned  in  order  to  re-ex- 
tinguish the  reflected  ray.  Several  other  substances  besides 
quartz,  such  as  oil  of  turpentine,  solution  of  sugar,  &c.,  possess 
the  power  of  rotating  the  plane  of  polarization.  The  apparatus 
far  showing  that  a  similar  rotating  power  is  possessed  by  mag- 
netism, is  represented  in  Fig.  257.  It  consists  of  two  very 

Fig,  257. 


The  effect  of  Magnetism  on  Polarized  Light, 


What  is  the  effect  of  quartz  and  some  oth^r  substances  upon  the  extinguished  ray? 
Describe  the  apparatus,  Fig.  2o7.  by  which  it  is  shown  that  magnetism  possesses  a  simi- 
lar power  of  deviating  a  polarized  ray  of  light. 


THE    PROGRESS    OF    DISCOVERY  507 

powerful  electro-magnets,  M  and  N,  mounted  horizontally  on 
two  iron  supports,  o,  o',  which  can  be  moved  on  a  support  K, 
The  current  from  10  or  11  Bunsen's  cells,  is  transmitted  by  the 
wire  A,  to  the  commutator  H,  by  which  it  may  be  sent  in  either 
direction  through  the  coil  M,  thence  by  the  wire  g  to  the  coil  N, 
and  then  back  again  by  the  wire  «,  to  the  commutator  H,  fina-Iy 
emerging  at  B.  The  two  cylinders  of  soft  iron  on  which  the  coils 
M  and  N  are  wound,  are  perforated  through  their  entire  length 
by  a  cylindrical  hole  so  as  to  allow  a  ray  of  light  to  pass  com- 
pletely through  them  both.  At  b  and  a,  there  are  two  of  Nicol's 
prisms,  each  consisting  of  sections  of  rhombohedral  crystals  of 
Iceland  spar,  which  have  been  cut  diagonally,  and  then  re-united 
by  Canada  balsam.  These  prisms  serve  instead  of  the  two  mir- 
rors spoken  of  a'  ove,  and  exert  a  similar  polarizing  effect  upon 
a  ray  of  light.  When  the  lamp  is  placed  opposite  b,  and  the  eye 
at  a,  the  ray  of  light  is  completely  extinguished.  If  at  this 
moment  there  be  placed  at  c,  a  plate  of  ordinary  or  flint  glass 
with  parallel  faces,  the  ray  of  light  is  still  extinguished  to  the  eye 
at  «,  so  !ongas  the  electro-magnets  remain  unexcited,  but  the  in- 
stant the  current  begins  to  flow  and  the  electro-magnets  become 
excited,  the  ray  of  light  will  reappear  and  cease  to  be  extin- 
guished by  the  prism  a,  and  to  extinguish  it  again  it  will  be 
necessary  to  turn  the  index  attached  to  a,  to  the  right  or  le  t 
through  a  certain  angle.  If  the  current  be  broken  the  light  re- 
appears ;  if  the  current  be  reversed,  and  the  poles  of  the  electro- 
magnets changed,  the  direction  in  which  the  index  must  be 
turned  in  order  to  extinguish  the  ray,  must  also  be  reversed. 
Ileive  it  appears  that  the  electric  current,  or  the  magnetic  power 
which  it  generates,  possesses  the  power  of  rotating  the  ray  of 
polarized  light  which  pas  es  through  the  core  of  the  magnets, 
or  else  imparts  this  power  to  the  piece  of  glass  placed  at  c,  and 
that  this  rotating  power  is  to  the  right  or  to  the  left,  according 
to  the  direction  of  the  electric  current,  and  is  acquired  and  lo  t 
instantaneously,  following  the  connection  with  the  battery.  "  Iu 
this  experiment,"  says  Mr.  Faraday,  "we  may  justly  say,  that 
a  ray  of  light  is  electrified  and  the  electric  forces  illuminated," 
The  general  conclusion  is,  that  the  connection  between  Elec- 
tricity, MagnetUm,  and  Light,  whether  the  light  emanates  from 
an  electrical  source,  or  from  ordinary  sources,  is  extremely 
intimate,  and  closely  connected  with  the  doctrine  of  the  con- 
vertibility of  Forces, 

What  is  rhe  general  conclusion  in  regard  to  the  connection  between  Electricity,  Mag- 
netism and  Light? 


508  IN   REGARD    TO    VOLTA-ELE-CTRIC 

477.  Progress  of  discovery  in  the  induction  of  Electricity 
by  the  Galvanic  current,  and  the  construction  of  Induction 
Coils  and  Mag-neto-Electric  Machines.  The  successive  dis- 
coveries which  led  to  the  construction  of  the  powerful  Induc- 
tion Coils  and  Magneto-Electric  machines  now  in  use,  are  as 
follows. — The  primary  fact  of  induction,  viz :  the  induction  of 
a  secondary  current  in  the  primary  wire  connecting  the  poles 
of  a  battery,  and  the  increased  effect  obtained  by  using  a  long 
wire,  and  especially  one  coiled  into  a  helix,  was  discovered 
by  Prof.  Henry  in  1831.  In  the  same  year  Mr.  Faraday  made 
the  discovery  of  the  induction  of  electricity  by  the  battery  cur- 
rent in  a  neighboring  wire,  distinct  from  it,  and  forming  a 
closed  circuit,  whenever  the  battery  circuit  is  completed  or 
broken ;  also,  whenever  the  battery  circuit  is  brought  near 
or  removed  from  the  closed  secondary  current.  He  also  di  > 
covered  at  the  same  time,  the  induction  of  electricity  by  a  mag- 
net, whenever  brought  near  or  removed  from  a  closed  circuit 
consisting  of  a  great  length  of  wire  coiled  into  a  helix ;  al  o, 
the  induction  of  electricity  in  a  similar  coil  by  the  magnetiza- 
tion and  de-magnetization  of  an  electro-magnet  by  a  battery 
current,  and  by  the  magnetization  and  de-magnetization  of  a 
piece  of  soft  iron  by  the  inductive  influence  of  a  permanent 
magnet  brought  near  and  removed  from  it.  In  1833,  Dal 
Negro,  an  Italian  philosopher,  discovered  that  the  inductive 
influence  of  the  current  of  the  primary  wire  connecting  the 
poles  of  a  battery,  was  more  intense  if  the  wire  were  wound 
into  a  coil  surrounding  a  piece  of  soft  iron.  In  1834,  Mr.  Far- 
aday made  the  announcement  of  the  same  fact,  communicated 
to  him  by  a  young  man  named  William  Jenkin,  of  London,  viz : 
"  that  if  an  ordinary  wire  of  short  length  be  used  as  a  medium 
of  communication  between  the  poles  of  a  battery  of  a  single 
pair  of  metals,  no  management  will  enable  the  experimenter  to 
obtain  an  electric  shock  from  this  wire ;  but  if  the  wire  which 
surrounds  an  electro-magnet  be  used,  a  shock  is  felt  each  time 
the  contact  with  the  electromotor  is  broken,  provided  the  ends 
of  the  wire  be  grasped,  one  in  each  hand."  This  fact  Faraday 
confirmed  by  his  own  experiments.  In  1836,  Dr.  Page  discov- 
ered the  principle  that  the  intensity  of  the  induced  current  in  the 
secondary  wire  might  be  greatly  increased  by  lengthening  the 
secondary  coil  and  making  it  many  times  longer  than  the  pri- 

477.  Who  discovered  the  fact  of  induction  in  the  primary  wire  coiled  into  a  helix? 
Who  discovered  the  inductive  action  of  the  primary  wire  upon  a  neighboring  wire  ?  Who 
discovered  the  increase  of  effect  produced  by  winding  the  primary  coil  arouad  a  piece, 
of  soft  iron  ?  What  was  the  discovery  made  by  Jeukiu '! 


AND    MAGNETO-ELECTRIC   INDUCTIOi..  509 

"v 

nary  coil ;  constructed  his  compound-coil  and  spark-arresting 
circuit-breaker,  and,  in  1838,  discovered  the  advantage  of  mak- 
ing use  of  a  number  of  soft  iron  wires  in  place  of  a  bar  of  solid 
iron  in  the  axis  of  the  inner  coil.  In  1853,  Fizeau  discovered 
the  peculiar  effect  of  the  condenser,  or  Leyden  jar,  in  absorbing 
the  extra-current  and  increasing  the  intensity  of  the  induced 
current  in  the  secondary  coil.  In  1857,  Ritchie  invented  his 
improved  mode  of  winding  and  insulating  the  secondary  coil 
and  breaking  the  circuit,  by  which  the  length  of  the  spark  was 
increased  to  fifteen  inches.  And  finally,  in  1860,  by  adopting 
this  improved  mode  of  winding,  and  by  greatly  lengthening 
the  secondary  coil,  Ruhmkorff  succeeded  in  bringing  his  induc- 
tion coil  to  its  present  state  of  perfection. 

In  the  development  of  Magneto-Electric  machines,  the  origi- 
nal discovery  of  the  induction  of  electricity  by  the  magnet,  and 
the  production  of  a  current  in  a  wire  wound  upon  soft  iron, 
by  the  approach  and  removal  of  a  strong  permanent  magnet, 
was  made  by  Mr.  Faraday  in  1831.  In  1832,  Pixii  constructed 
his  machine,  in  which  a  magnet  was  made  to  revolve  in  front 
of  fixed  coils.  In  1833,  Saxton  constructed  his  improved  ma- 
chine, in  which  the  magnets  were  fixed,  and  the  coils  made  to 
revolve ;  and  in  1 833,  Page  made  still  further  improvements 
by  increasing  the  number  of  the  magnets  and  inducing  magnet- 
ism at  both  extremities  of  the  iron  cores  within  the  coils,  and 
invented  his  pole-changer,  by  which  each  pole  always  received 
the  same  kind  of  electricity,  and  one-half  the  electric  current 
previously  lost,  was  saved.  In  1861,  Holmes  invented  thfj 
combination  of  magneto-electric  machines,  which  resulted  in 
the  production  of  the  permanent  magneto  electric  light,  and  its 
introduction  for  Light-house  illumination.  This  was  followed 
by  Wilde's  machine  in  1866,  and  by  Ladd's  in  1867,  by  which 
the  Magneto-Electric  machine  has  been  advanced  to  its  most 
perfect  state,  and  brought  to  supersede  the  light  of  the  sun  for 
photographic  pictures.  All  these  wonderful  inventions  and 
their  applications,  directly  connected  with  fome  of  the  greatest 
improvements  in  modern  civilization,  derive  their  origin  from 
the  discovery  by  Mr.  Faraday,  in  1831,  of  the  induction  of  elec- 
tricity by  magnetism,  and  the  production  of  the  electric  spark 
by  a  fixed  magnet ;  and  therefore,  with  justice  might  he  say,  in 
the  latter  part  of  his  life,  in  speaking  of  the  attempts  by  Mr. 

Who  discovered  the  advantage  of  lengthening  the  secondary  coil?  Who  first  made 
use  of  the  Condenser?  What  was  Ritchie's  improvement?  Ruhmkorff  ;s?  Trace  the 
order  of  progression  in  the  construction  of  Magneto-Electric  Machines.  Jo  whose  dis- 
covery is  the  Magneto-electric  light  of  Light-houses  strictly  due? 


510 


THERMO-ELECTRICITY. 


Holmes  at  introducing  the  magneto-electric  light  into  the  Light- 
house at  the  South  Foreland,  a  subject  in  which  he  was  much 
interested, — "  I  will  not  tell  you  that  the  problem  of  employing 
the  magneto-electric  spark  for  Light-house  illumination,  is  quite 
solved  yet,  although  I  desire  it  should  be  established  most 
earne  ?tly,  for  I  regard  this  magnetic  spark  as  one  of  my  own 
offspring." 


§  V2.    Thermo-Blectricity. 

478.  Heat  producss  Electricity.  We  have  seen  that  Elec- 
tricity pro  luces  Heat :  it  is  found  that  the  reverse  is  also  true, 
arid  that  Heat  under  certain  circum  tances  produces  Electricity. 
If  metallic  bars  of  unequal  conducting  power  for  heat  be 
soldered  together  at  one  extremity,  and  heat  applied  at  the 
point  of  junction,  the  other  extremity  of  the  bars  being  con- 
ne^tel  wiih  the  galvanometer,  an  electric  current  will  be  at 
once  produced,  flowing  irom  the  hotter  to  the  colder  metal. 
Tiius,  in  Fig.  25,8,  let  m  n,  be  a  bar  of  copper,  whose  ends 

are  bent  down 

Fig-  258.  and    soldered 

to  a  plate  of 
bismuth,  p  o, 
and  let  a  mag- 
netic needle 
be  mounted 
upon  a  pivot 
in  the  space 
between  the 
plates,  and  the 
apparatus  be 
pLicerl  in  the 
magnetic  me- 
ridian;  on 
applying-  the 

heat  of  a  lamp  at  o,  the  needle  will  be  at  once  detieL-ted  in 
such  a  mann  T  as  to  show  the  passage  of  a  current  of  elec- 
tricity from  n  to  m,  in  the  direction  indicated  by  the  arrow. 
If  instead  of  applying  heat  at  0,  a  piece  of  ica  be  placed  at 
that  point,  or  cotton-wool  moistened  with  ether,  while  the  juuc- 


Electricity  produced  by  Heat. 


478    Prove  that  Heat  produces  Electricity.     Describe  F/6-.  258- 


THE    THERMO-ELECTRIC  511 

tion  at  m  retains  its  natural  temperature,  there  will  be  a  cur- 
rent in  the  opposite  direction,  from  m  towards  n,  and  the 
energy  of  the  current  will  be  proportioned  to  the  difference 
of  temperature  between  the  two  junctions.  The  current  is 
always  from  the  hotter  to  the  colder  metal :  it  has  been  found 
that  the  currents  are  produced  equally  well  in  vacua  and  in 
hydrogen,  and  therefore  are  not  due  to  chemical  action.  The 
true  cause  is  the  unequal  propagation  of  heat  from  the  heated 
junction.  Any  obstruction  to  the  equal  distribution  of  heat 
in  a  metallic  conductor,  generates  a  current  of  electricity,  i.i 
t'.ie  same  way  that  any  obstruction  to  the  flow  of  the  electric 
current  in  a  metallic  wire  produces  a  rise  of  temperature. 
T>vo  metals  are  not  necessary  to  the  evolution  of  the  cur- 
rent: any  disturbance  of  the  molecular  arrangement  so  a>  to 
interfere  with  the  equal  propagation  of  the  heat  from  the 
hot  to  the  cold  portions  of  a  bar  composed  of  a  single 
metal,  is  sufficient  to  produce  an  electrical  current.  Thus  a 
straight  platinu:n  wire  stretched  between  the  binding  screws 
of  a  g  ilvanometer,  may  be  heated  at  any  point  without  de- 
veloping the  slightest  current  in  the  instrument :  but  if  the 
platinum  wire  be  twisted  into  a  loop  so  that  its  molecular  ar- 
rangement is  slightly  altered  at  this  point,  and  heat  be  applied 
close  to  the  loop  and  to  the  right  of  it,  a  current  will  circulate 
through  the  galvanometer  from  right  to  left,  owing  to  the  un- 
equal conduction  of  the  heat.  These  facts  were  ascertained  by 
Seebeck  at  Berlin,  in  1821,  and  are  of  great  interest  as  show- 
ing the  intimate  connection  between  Heat  and  Electricity.  It 
may  be  stated  in  general  that  when  two  metals,  of  unequal  con- 
ducting power  for  heat,  are  connected  in  any  way  so  as  to  form 
a  closed  circuit,  an  electrical  current  is  established  flowing  from 
the  hotter  to  the  colder,  whenever  a  different  temperature  is 
produced  between  them,  and  the  current  is  maintained  as  long 
as  any  difference  of  temperature  continues.  The  metal  from 
which  the  current  proceeds  is  exactly  analogous  in  situation  to 
the  zinc  plate  in  the  battery ;  the  metal  to  which  the  current 
proceeds  is  analogous  to  the  platinum  plate.  The  different  metals 
do  not  all  possess  this  power  when  associated ;  and  the  direc- 
tion of  the  current  depends  upon  the  rnetals  which  compose  the 
circu't.  When  bars  of  a  itimo  ly  and  bismuth  are  soldered  to- 
gether and  heated  at  th;i  junction,  the  current  flows  from  the 

Does  the  cat  rent  flow  from  the  hot  to  the  cold  metal  or  the  reverse?  What  is  the 
effect  if  there  be  any  obstruction  to  th<>  equal  proposition  of  hent  in  a  metall'o  con- 
d'lot/n-?  VFhat  always  takes  place  when  two  metal*  of  unequal  conducting  power  are 
connected  so  as  to  form  a  closed  circuit  and  heated  ? 


512 


BATTERY. 


cold  end  of  the  bismuth  to  the  cold  end  of  the  antimony,  as 
represented  in  Fig.  258.  The  following  series  represents  the 
thermo-electric  order  of  the  metals,  each  metal  being  positive 
in  reference  to  the  metals  which  come  after  it, — Bismuth,  Mer- 
cury, Lead,  Tin,  Platinum,  Copper,  Silver,  Zinc,  Iron,  Antimony. 
When  heated  together,  the  current  proceeds  from  the  cold 
extremities  of  those  which  are  first  on  the  list  to  the  cold  ex- 
tremities of  those  which  are  last.  The  thermo-electric  order  is 
very  different  from  the  voltaic  order.  Other  substances  besides 
the  metals  will  also  produce  electrical  currents  when  soldered 
together  and  heated.  Gas-carbon  may  be  used  in  connection 
with  German-silver,  with  silver,  and  with  iron,  and  it  has  even 
been  found  that  the  point  of  a  heated  cone  of  porcelain,  if  brought 
into  contact  with  a  cold  cylinder  of  the  same  material,  will  gen- 
erate a  thermo-electric  current  passing  from  the  hot  cone  to  the 
cold  cylinder,  each  being  connected  with  the  galvanometer  by 
cotton  soaked  in  some  conducting  liquid. 

When  the  process  is  reversed,  and  a  weak  galvanic  current 
is  transmitted  through  a  thermo-electric  series,  heat  i*  produced 
if  the  current  be  sent  in  the  same  direction  as  the  thermo-elec- 
tric current,  and  cold  if  in  the  reverse  direction. 

479.    The  Thermo-electric  Battery.     By  connecting   the 
col< I  bismuth  end  of  a  thermo-electric  pair- 
Fig.  259.  composed  of  antimony  and  bismuth,  with  the 
cold    antimony  end  of   a   second   pair,    as 
shown  in  Fig.  259,  the  bismuth  being  repre- 
Tiiermo-dectric  Pile,     sented  by  the  white  bar,  and  the  antimony 
by  the  black,  and  so  through  a  long  series, 
a    battery  may   be    constructed,     the 
power  of  which  increases  with  every 
additional  pair.     While    the   ends  of 
the  pairs  on  one  side  must  be  heated, 
those    on  the  other  side  must  be  kept 
cool,  in  order  to  obtain  the  most  pow- 
erful effects.     When  arranged   as   in 
Fig.  260,   the  extremities    of  the  se- 
ries being  connected    with  a  galvan- 
ometer by  means  of  wires,  upon  the 
application  of  heat  at  the  upper  ends,  the 
needle    is    powerfully    deflected,    and 
iodide   of    potassium    and    acidulated 
water  may  be  decomposed.     The  legs 


of  a  fro"1  may 

conyulsions 


even   be  thrown  into 

the    current    proceed, 


NOBILl's    THERMO-ELECTRIC    BATTERY.  513 

ing  from  a  single  pair.  If  the  lower  ends  of  the  pairs  be 
heated  while  the  upper  are  kept  cool,  the  direction  of  the 
current  will  be  reversed.  The  intensity  of  the  current  is 
feeble,  but  in  quantity  it  closely  resembles  a  weak  galvanic 
circuit:  its  chief  effect  is  therefore  magnetic,  and  a  battery 
composed  of  sixty  pairs  of  bismuth  and  antimony  bars,  three 
inches  long,  three -fourths  of  an  inch  wide,  and  one-fourth  of 
an  inch  thick,  whose  extremities  on  one  sida  are  heated  by  a 
hot  plate  of  iron,  and  on  the  other  cooled  by  immersion  in  snow 
mixed  with  half  its  weight  of  salt,  will  produce  an  electro- 
magnetic current  sufficient  to  raise  a  weight  of  fifty  pounds. 

430.  The  Thermo-electric  Battery  of  Nobili.  The  first 
thermo-electric  battery  was  constructed  by  Oersted  and  Fourier, 
but  Nobili  was  the  inventor  of  the  arrangement  now  generally 
used  ;  he  united  bars  of  bismuth  and  antimony  in  such  a  way  as 
to  form  a  series  of  five  pairs,  the  bar  of  bismuth  b,  being  con- 
nected with  the  lower  an- 

Fig.  262.  Fig.  261.  timony  bar  of  a  second 

similar  series  placed  ver- 
a  +       tically  by  the  side  of  the 
g™-^—^      first?  Ffgm  261,  then  the 

&" ."  ;''  ^'^-g      last  bismuth  of  this  series 

£;';•/   r'  '•  "'ZjJ£      with  the  first  antimony  of 
£~~ ZZZI~§>      a  third,  and  so  on  for  four 
If'"-       vertical  series  containing 
20  couples,  the  whole  se- 
ries commencing  with  a 

NobiWs  Thermo-electric  Battery.  bar  of  bismuth  and   end- 

ing with  one  of  antimony. 

The  pairs  were  insulated  by  means  of  bands  of  paper  covered 
with  varnish,  and  then  enclosed  in  a  brass  case,  in  such  a 
manner  that  the  junctions  of  the  bars  appeared  at  the  opposite 
ends  of  the  case,  Fig.  262.  Two  binding  screws,  x  and  y,  insu- 
lated by  ivory  and  communicating,  the  one  with  the  first  anti- 
mony, and  the  other  with  the  last  bismuth  bnr,  constitute  the 
poles  of  the  battery,  and  admit  of  the  attachment  of  wires 
connecting  with  a  galvanometer,  as  represented  in  Pi?.  263. 
When  thus  connected,  the  slightest  difference  of  temperature 
between  the  two  ends  of  the  battery  is  sufficient  to  excite  a 

What  is  the  thermo-electric  order  of  the  metals?  Will  any  but  metillic  substances 
answer  ?  What  is  the  effect  of  transmitting  an  electric  current  through  a  thermo-elec- 
tric series? — 479.  Describe  the  thermo  el  ctric  battery.  What  are  its  effects?  Wliat  is 
its  magnetic  power? — 480.  Describe  the  therino  electric  battery  of  Nobili. 


514 


MEL L ONI* S    TIIEllMO— MULTIPLIER. 


current  of  electric- 
ity, and  produce  a 
very  sensible  de- 
flection of  the  nee- 
dle of  the  galvan- 
ometer. 

481.  TheTher- 
mo-IVXurtiplicr  of 
melloni.  Nobili's 
battery  thus  ar- 
ranged and  con- 
nected with  a 
galvanometer,  is 
the  instrument 
with  which  Mello- 
ni made  his  cele- 
brated researches 
in  regard  to  the 
transmission  of 

heat  through  screens,  §  88,  and  proved  the  existence  of  a  calorific. 

tint  for  heat  in  thin  plates  similar  to  the  colorifc  tint  for  light. 

It  was  named  by  him  the  Thermo-Multiplier,  Fig.  2G3.     The 

Fig.  264. 


Tke  Tiitrnw-eUctric  Multiplier  for  measuring  heat. 


MeUoni's  apparatus  for  measuring  thf  transmission  of  radiant  heat  by  the  Thermo- 
Multiplier. 

arrangement  of  his  apparatus  was  as  follows,  Fig.  2G4.     Upon  a 


FARMER'S  THERMO-ELECTRIC  515 

tablet  of  wood,  a  brass  rule  was  mounted,  about  a  yard  in  length, 
and  carefully  graduated.  This  rule  supported  at  varying  d  s- 
tances  the  different  pieces  of  which  the  apparatus  was  composed ; 
on  a  stand  a,  was  mounted  the  locatelli  lamp,  or  other  source  of 
heat ;  then  the  screens  F  and  E  ;  then  a  second  support  c,  on 
which  were  placed  the  substances  whose  diathermic  power  was 
to  be  determined;  and  finally  the  thermo-electric  pile  m,  who^e 
poles  A  and  B,  were  connected  with  the  galvanometer  D,  by  short 
and  thick  wires.  The  diathermic  power  of  the  substances  in  ques- 
tion was  determined  by  the  degree  of  deflection  in  the  galvan- 
ometer. A  thermo-electric  pile,  with  galvanometer  attached, 
wa?  also  the  instrument  used  by  Tyndall  in  his  experiments 
upon  the  absorption  and  transmission  of  radiant  heat  by  gases, 
described  in  his  work  entitled,  ''Heat  a  Mode  of  Motion'' and  it 

constitutes  the  most  delicate  known 
Fig.  265.  instrument   for    measuring   slight 

degrees  of  heat.  The  heat  of  the 
hand  at  the  distance  of  several 
feet,  warm  air  breathed  from  the 
mouth,  or  even  the  heat  produced 
by  the  impinging  of  compressed 
air  upon  one  end  of  the  battery, 
the  temperature  of  insects,  Fig. 
265,  and,  on  the  other  hand, 

The  temperate  ejects  measured        eV™ll7  slight  depressions  of   tem- 
by  the  Tker mo-Multiplier,  perature    at     the    OppO-lte    CJld    of 

the  battery,  all  produce  a  re- 
markable deflection  of  the  needle,  and  are  capable  of  being 
measured  by  it. 

482.  Farmer's  Thermo-Electric  Battery.  A  thermo-elec- 
tric battery  has  recently  been  constructed  by  Mr.  Farmer,  the 
inventor  of  the  Electric  fire-alarm,  §430,  which  may  be  substituted 
with  great  advantage  for  the.  galvanic  batteries  and  magneto- 
electric  machines  in  common  use.  A  series  of  pairs  of  German- 
silver  and  bismuth,  are  arranged  with  their  soldered  extremities 
pointing  towards  a  common  centre,  in  such  a  manner  as  to 
make  a  perfect  circle,  1,  Fig.  26t>;  the  electric  current  circu- 
lates from  pair  to  pair,  and  finally  appears  at  the  polar  binding 
screws ;  by  means  of  these  screws  the  current  may  be 
transmitted  to  the  binding  screws  of  a  second  series,  2,  entirely 

4Q1.  Describe  Melloni's  Thermo-multiplier.  Describe  the  arrangement  Of  Melloni'g 
apparatus  for  measuring  t'.ie  transmission  of  radiant  heat.  What  sligat  degrees  o/ tem- 
perature can  be  uie.i3ureJ.  by  tais  iuitruaieut? 


516 


BATTERY. 


Farmer' 's   Thermo- Electric  Battery. 


insulated  from 
the  first,  and  pro- 
ducing a  similar 
current,  and 
thence  to  a  third, 
finally  emerging 
at  the  poles. p  and 
n.  In  order  to 
actuate  this  bat- 
tery, it  is  only 
necessary  to  ap- 
ply heat  within 
the  internal  cylin- 
der to  which  the 
pairs  point.  This 
may  be  done  by 
means  of  charcoal, 
gas,  or  an  alcohol 


lamp.  In  Fig.  266,  G  is  a  tube  connecting  with  a  ga— burner, 
B  is  the  ga^-burner  of  the  battery,  c  is  a  deflector  to  keep  the 
h«jat  down  in  the  centre.  All  that  is  required  to  put  the  battery 
in  operation,  is  to  turn  on  the  gas  and  light  the  burner  B  ;  it  ac- 
quires its  maximum  of  activity  in  a  few  moments,  and  works 
con'inuously  and  constantly  as  long  as  it  receives  heat,  pro- 
ducing a  steady  and  perfectly  uniform  current  of  electricity 
for  an  indefinite  period,  without  any  perceptible  variation  in 
strength.  It  may  be  employed  for  any  of  the  purposes  for 
which  a  common  galvanic  battery  is  used, — for  working  the 
telegraph,  precipitating  metals  from  their  solutions,  exciting 
electro-magnets,  operating  fire-alarms,  producing  the  electric 
light,  or  actuating  Page's  or  Ruhmkorff's  coils  for  medical 
use,  and  is  particularly  adapted  to  electrotyping,  plating  and 
gilding,  because  no  acids,  mercury,  or  liquids  of  any  kind  are 
required.  There  is  no  waste  of  the  metallic  pairs,  as  they  re- 
main as  good  at  the  end  of  the  year  as  when  first  used.  It 
requires  no  attention  after  being  first  lighted,  and  will  run 
day  and  night  without  any  change,  as  long  as  heat  is  applied. 
It  is  also  very  economical,  as  five  or  six  pounds  of  coal 
will  evolve  as  much  electricity  as  one  and  a  half  pounds  of 
zinc,  five  or  six  pounds  of  sulphuric  acid,  and  one  ounce  of 
mercury.  Ten  pairs  are  estimated  to  be  equal  to  one  Smee's 
cell ;  twenty -four  pairs  to  one  Daniell's  cell,  and  forty-four  to 

482.    Describe  Farmer's  Thermo-electric  battery.     What  is  required  to  put  this  bat- 
te'-v  into  operation  ?    For  wliat  purposes  may  it  be  employed  ?     Wiiat  are  its  ad  vantages  ? 


ANIMAL  517 

P 

one  Grove's  cell.  The  cost  of  working  such  a  ba'tery  possessing 
half  the  power  of  a  G/ove  cell,  and  five  times  that  of  a  Daniell, 
is  one-third  of  a  cent  per  hour  with  gas,  and  two  cents  per  hour 
with  an  alcohol  lamp.. 

It  has  been  estimated  that  a  light  equal  to  that  of  5,000 
can:lles,  can  be  produced, 

By  a  Grove's  battery,  at  a  cost  of,  per  candle,  per  hour,  of  5^  mills.     / 

By  Illuminating  Gas, 1       u 

By  S:nee's  battery, 1  , 

By  the  Magneto-electric  machine,          .         .         .  0.10  " 

Also,  that  from  one  pound  of  coal  used  in  the  steam-engine  to 
drive  the  magneto-electric  machine,  or  in  the  thermo-electric 
battery,  a  light  equal  to  that  of  about  144  candies  can  be  ob- 
tained :  also  that  the  total  electrical  energy  contained  in  one 
pound  of  pure  carbon,  completely  burned  into  carbonic  acid, 
and  its  heat  used  to  produce  electricity,  and  through  electricity 
converted  into  Light,  will  furnish  an  amount  equal  to  that  of 
a  candle  burning  1  year  and  5  months  ;  and  that  if  all  the  energy 
in  a  pound  of  carbon  could  be  converted  into  Light  by  means  of 
the  electricity  which  it  is  capable  of  generating,  it  would  be 
equivalent  to  the  burning  of  acindle  for  12,410  hours. 

This  will  give  soma  idea  of  th'3  tremendous  amount  of 
energy  capable  of  being  furnished  by  the  electricity  derived 
from  Heat. 


§  VIZ.    Animal  Electricity. 

483.  Animal  Life  produces  Electricity.  The  vital  prin- 
ciple of  the  Animal  economy  in  all  animals  produces  Elec- 
tricity, and  in  soni3  animals  is  capable  of  generating  very 
powerful  electrical  currents.  The  torpedo,  a  flat  fish,  found 
in  the  Mediterranean,  is  provided  with  two  electrical  organs, 
situated  one  on  eac;h  side  of  the  spine,  near  the  head,  and 
a  powerful  shock  is  received  on  simultaneously  touching  the 
back  and  the  belly  of  the  fish  at  any  part;  but  the  strongest 
shock  is  obtained  immediately  over  the  two  organs.  The 
gymnotus,  a  fresh  water  fish,  abundant  in  the  waters  of  the 
Orinoco,  has  four  electrical  organs,  running  from  the  head 
to  the  tail  of  the  animal.  So  great  is  the  electrical  energy 

State  the  comparative  expeise  of  producing  a  light  equal  to  that  of  5030  candles  from 
Grove's  battery,  Smco's,  Illuminating  Gas,  and  the  Magneto-electric  machine.  State  the 
total  electrical  energy  contained  in  one  pound  of  coal.  State  the  jllumiuatiug  power 
of  one  pouud  of  Carbon,  if  converted  into  light. 


518  ELECTRICITY. 

of  the  animal  that  a  fish  40  inches  in  length,  has  given  a 
shoek  which,  it  has  been  calculated,  is  equal  to  that  emitted 
from  a  Leyden  battery  of  15  jars,  exposing  3500  square  inches 
of  coated  surface.  The  shocks  from  the  gymnotus  are  sufficient 
to  stun,  and  even  kill,  large  fish ;  and  give  rise  to  electric  cur- 
rents of  enough  power  to  deflect  the  galvanometer,  mag- 
netize a  needle,  decompose  iodide  of  potassium,  and  even  pro- 
duce sparks.  It  has  been  shown,  also,  that  in  all  living  ani- 
mals an  electrical  current  is  perpetually  circulating  between  the 
interior  of  the  muscles  and  their  external  surface,  probably 
due  to  the  vital  changes  which  are  continually  going  on  in  the 
organic  tissue.  In  warm-blooded  animals,  this  current  ceases  in 
a  very  few  minutes  after  death ;  but  in  cold-blooded  animals,  it 
continues  for  a  much  longer  period.  If  five  or  six  frogs  be 
killed  by  dividing  the  spinal  column  just  below  the  head,  the 
lower  limbs  removed,  and  the  skin  stripped  from  them,  the 
thighs  separated  from  the  lower  legs  at  the  knee  joint,  and  then 
cut  across  transversely,  a  battery  can  be  constructed  from  the 
pieces.  Thus,  let  the  lower  half  of  the  thighs  be  placed  upon 
a  varnished  board,  and  arranged  so  that  the  knee  joint  of  one 
limb  shall  be  in  contact  with  the  transverse  section  of  the  next, 
and  a  muscular  pile  can  be  formed,  consisting  of  ten  or  twelve 
pairs ;  the  terminal  pieces  should  be  made  to  dip  i:i*to  small 
cavities,  in  which  distilled  water  is  placed.  If  the  wires  of  a 
galvanometer  be  introduced  into  these  cavities,  by  means  of  two 
thin  platinum- plates,  a  deviation  in  the  needle  will  be  observed 
ia  such  a  direction  as  to  show  the  existence  of  a  current  passing 
from  the  centre,  or  cut  transverse  end  of  the  muscle,  towards 
its  exterior.  This  muscular  pile  acts  equally  well  in  highly 
rarefied  air,  in  carbonic  acid  gas,  and  in  hydrogen ;  in  the  last 
gas  the  needle  of  the  galvanometer,  after  being  moved,  remains 
stationary  for  several  hours.  This  nullity  of  the  action  of  the 
several  gases  is  thought  to  prove  that  the  oxygen  of  the  air  is 
not  necessary,  and  that  the  origin  of  the  current  is  in  the  muscle 
itself,  and  depends  rather  on  the  organization  of  the  muscular 
fibre  and  the  chemical  actions  going  on  within  its  structure.  If 
a  prepared  frog  be  placed  with  its  lumbar  nerves  plunged  into 
one  capsule  filled  with  water,  and  its  legs  placed  in  another,  th3 
circuit  being  completed  through  the  galvanometer,  the  ins:ru- 
ment  gives  indications  of  an  electrical  current  passing  from  the 
foet  towards  the  head  of  the  animal.  The  effect  is  very  much 

4S3.  Can  the  vital  principle  of  animals  produce  electricity  ?  Describe  the  torpedo. 
What  effaot?  are  produce  i  b 7  it  ?  Is  t  icre  an  electrical  current  circulating  in  all  a:ii- 
mab  ?  D3^.?ib3  1 13  fro^  battery.  Ho,r  is  it  sho,rn  that  thz  current  ia  not  produced  by 
the  action  of  the  air  ? 


THE   PHYSIOLOGICAL 


519 


Fig.  252. 


increased  when  several  frogs  are  arranged  on  an  insulated  sur- 
face in  the  manner  shown  in  Fiy.  252,  the  spinal  cord  of  each  frog 
touching  the  legs  of  the  following;  every  time  the  circuit  is 
completed,  the  needle  of  the  galvanometer  moves,  and  the 
limbs  of  the  frogs  contract.  It  is  probable  that  further  inves- 
tigation will  develop  a  still  closer  relation 
between  electricity  and  the  vital  force  of 
the  Animal  economy. 

484.  The  Physiological  ejects  of  the 
Galvanic  Current.  On  the  other  hand  the 
physiological  effects  of  the  galvanic  cur- 
rent upon  the  animal  economy  are  equally 
remarkable.  The  convulsive  movements  i.i 
the  leg  of  the  frog,  noticed  by  Galvani,  led 
to  the  invention  of  the  voltaic  pile,  and  the 
formation  of  a  new  scien>  e.  When  the 
wire  from  one  pole  of  the  battery  is  put 
in  communication  with  the  nerve  of  any 
1  \\f\fllJ  limb  of  an  animal  recently  killed,  Fig.  2.">3, 

I  »\   I  IM  and  the  wire  from  the  other  pole  with  the 

outside  of  the  muscles,  the  limb  will  1  e 
contracted  with  great  violence,  the  musdes 
of  the  face  will  be  made  to  di  play  the  va- 
rious emotions  and  passions  of  the  mind,  and 
many  of  the  vital  processes  of  secretion  and 
digestion  will  be  recommenced,  so  that  there 
is  good  reason  for  supposing  a  close  connec- 
tion between  the  galvanic  current  and  the 
nervous  energy  by  which  all  the  vital  func- 
tions are  maintained. 

By  means  of  a  powerful  galvanic  current, 
small  animals,  such  as  rabbits  and  hares, 
which  have  been  suffocated  half  an  hour,  have 
been  brought  to  life.  The  face  of  a  prisoner,  who  had  been  exe- 
cuted by  hanging,  exhibited  such  dreadful  muscular  contortions 
when  exf'ited  by  the  galvanic  current,  as  to  horrify  the  spectators  : 
the  trunk  partially  raised  itself,  the  Innds  were  agitated  and  the 
arm-<  swung  wildly,  the  chest  rose  and  fell  as  though  respira- 
ti-m  had  recommenced,  and  nearly  all  the  vital  processes  were 
set  in  motion  ;  but  the  whole  effect  ceased  as  soon  as  the  current 


Battery  c 

tiie  legs  of  Frogs. 


Describe  the  arrangement  of  the  frog  battery.—  484      State  the   physiological 
of  k'ie  curroi*-.     What  is  the  effect  upon  small  animals  that  have  been  suffocated?    Pe- 
ecribe  the  effect  upon  an  executed  prisoner. 


520  EFFECTS  OF  THE 

•> 

was  withdrawn.  If  the  fingers  be  moistened  and  applied  to  the 
poles  of  the  battery,  a  smart  shock  \rill  be  obtained,  the  strength 
of  which  will  depend  upon  the  number  of  plates  or  cells  em- 
ployed ;  if  two  metallic  handles  be  connected  with  the  two  poles, 
and  grasped  by  the  moistened  hands,  the  strength  of  the  con- 
tinued succession  of  shocks  will  be  greatly  increased.  The 

Fig.  253. 


Tht  effect  of  the  Galvanic  current  on  the  Animal  economy. 

most  severe  shocks  are  given,  however,  not  by  the  direct  cur- 
rent of  the  battery,  but  by  the  induced  currents  of  Page's  and 
Ruhmkorff  s  coils,  and  the  various  Magneto-electric  machines. 
Shocks  of  great  violence  can  thus  be  given,  and  so  firm  a  mus- 
cular contraction  of  the  hands  produced,  that  it  Avill  be  impos- 
sible to  relax  the  grasp.  It  has  also  been  found  that  these  in- 
duced currents  exert  a  different  effect  upon  the  system,  from  tlio 
direct  current  of  the  battery,  and  do  not  produce  the  same  chem- 
ical disturbance  of  the  functions  of  the  body.  Various  instru- 
ments have  been  invented  for  the  application  of  these  currents 
to  medical  purposes.  Of  these  the  most  efficient  is  Page's  sep- 

How  can  shocks  be  taken  from  the  battery  ?    What  is  the  effect  of  using  metallic 
bandies  ?    By  what  instruments  can  the  most  severe  shocks  be  obtained  ? 


GALVANIC    CURRENT.  521 

arable  helices  §  451,  with  the  coils  arranged  horizontaHy,  on  ac- 
count of  the  facility  with  which  the  shocks  may  be  regulated. 
With  this  apparatus,  there  are  some  peculiarities  in  the  shock 
depending  upon  the  motion  of  the  battery  wire  over  the  rasp : 
if  it  is  moved  slowly,  distinct  and  powerful  shocks  are  expe- 
rienced ;  if  the  motion  be  more  rapid,  the  arras  are  much  con- 
vulsed :  and  if  it  be  drawn  very  rapidly,  the  succession  or'  shocks 
becomes  intensely  painful.  The  violence  of  the  shocks  can  be 
easily  regulated  by  the  number  of  iron  wires  employed,  and  by 
varying  the  distance  to  which  they  are  inserted.  The  power 
of  the  shock  depends  very  much  upon  the  extent  of  the  contact 
surface  between  the  hands  and  the  metallic  conductors ;  if  two 
wires  only  are  used,  and  held  lightly  in  the  fingers,  the  effect  is 
much  less  than  when  metallic  handles  are  employed  especially  if 
the  hands  are  moistened  with  salt  water.  Shocks  of  a  peculiar 
character  may  be  given  by  placing  the  polar  wires  in  two  ba- 
sins of  water,  and  then  dipping  a  hand  into  each  basin ;  in  this 
ca>e  the  strongest  sensation  is  experienced  when  the  ends  of  the 
fingers  only  are  immersed;  if  a  large  surface  be  exposed  the 
shock  will  be  felt  strongly  through  the  arm?.  The-e  shocks 
will  pass  without  much  diminution  of  intensity  through  a  circle 
formed  of  several  persons,  although  different  individuals  are 
very  differently  affected,  the  shock  which  is  felt  by  some  only 
in  the  fingers  or  hands,  in  the  case  of  others  extending  to  the 
arms  and  breast.  There  is  a  difference  in  tho  strength  of  the 
shocks  in  the  two  arms ;  if  the  positive  handle  be  held  in  the 
right  hand  and  the  negative  in  the  left,  the  left  hand  and  arm 
will  experience  the  strongest  sensations,  and  be  the  most  con- 
vulsed. This  remarkable  difference  of  inten-ity  is  believed  to 
be  a  purely  physiological  peculiarity,  a  greater  effect  being  pro- 
duced by  the  current,  in  the  arm  in  which  it  flows  in  the  same 
direction  as  the  ramification  of  the  nerves,  than  in  the  one  in 
which  it  flows  in  an  opposite  direction.  If  both  wires  are  put 
into  the  same  trough  at  some  distance  apart,  and  a  finger  of 
each  hand  be  placed  in  the  water  in  a  line  between  the  two 
wires,  a  shock  will  be  felt,  because  the  current  finds  a  passage 
through  the  body  more  readily  than  through  the  water,  which 
intervenes  between  the  fingers ;  but  if  the  fingers  be  put  in  at 
right  angles  to  the  line  between  the  wires  no  shock  will  be  felt : 
if  the  conducting  power  of  the  water  be  made  better  than  that 

How  can  the  violence  of  the  shocks  he  regulated  1  What  is  the  effect  of  taking:  the 
shocks  through  water?  Is  there  any  difference  in  the  effect  upon  the  two  arms  ?  How 
may  the  effect  of  the  shock  from  water  be  increased  ? 


522  THE    VARIOUS     SOURCES    OF    ELECTRICITY. 

of  the  body,  by  dissolving  in  it  a  little  common  salt,  little  or  no 
shock  can  be  perceived.  It -has  also  been  ascertained  that  in- 
duced currents  of  different  orders  produce  different  effects  upon 
the  body.  An  induced  current  of  the  first  order,  produces 
strong  muscular  contractions,  but  has  little  effect  upon  the  sen- 
sibility of  the  skin,  while  an  induced  current  of  the  second  or- 
der increases  the  cutaneous  sensibility  to  such  a  degree,  that  it 
often  cannot  be  applied  to  persons  of  great  nervous  susceptibility. 
485.  The  various  sources  of  Electricity,  and  its  Relations 
to  the  other  two  Chemical  Agents,  Heat  and  Lig-ht.  The 
study  of  Static  and  Galvanic  Electricity  has  shown,  that 
this  wonderful  agent  can  be  produced  by  a  great  variety  of 
sources: — by  Friction;  by  Chemical  action;  by  Magnetism; 
by  Heat ;  and  by  Vital  action.  It  has  also  shown  that  it  is 
capable  of  producing,  or  of  being  converted  into,  all  the  Forces, 
which  act  on  matter,  except  Gravity,  viz, — Motion ;  Heat ; 
Light ;  Chemical  action  ;  and  Magnetism  ;  and  that  it  can  imitate 
the  effects,  if  riot  actually  produce  several  of  the  properties 
of  the  Vital  Force. 

It  is  distinguished  from  the  other  Forces  by  producing  more 
intense  and  powerful  effects.  The  heat  which  it  generates  is 
the  most  intense  heat  known  ;  the  light,  which  it  evolves  is  su- 
perior to  the  light  of  the  Sun ;  the  motion  which  it  causes  is 
infinitely  more  rapid  and  prompt  than  any  which  can  be  brought 
about  by  the  more  tardy  operation  of  either  Heat  or  Light : 
the  physiological  sensations  which  it  exerts  are  more  decided, 
and  evident  than  those  of  the  other  forces.  It  is  especially  re- 
markable for  the  extraordinary  influence  which  it  exerts  over 
chemical  affinity.  It  is  able  to  break  up  and  destroy  some  of 
the  mo-t  powerful  combinations  existing  in  Nature,  and  has  dis- 
closed the  existence  of  a  very  large  number  of  the  chemical 
elements  known  to  the  chemist.  It  stands  out,  therefore,  as  in 
some  respects  superior  to  the  forces  of  Heat  and  Light.  Con- 
sequently it  is  a  more  prominent  and  valuable  agent  for  the  mod- 
ification and  control  of  Chemical  affinity  than  either  Heat  or 
Light,  and  is  emphatically  the  chief  instrument  which  the 
chemist  has  at  command  in  his  investigations  into  the  constitu- 
tion of  matter  for  the  purpose  of  determining  its  composition 
and  the  nature  of  the  elements  which  enter  into  it. 

What  different  effects  do  induced  currents  of  different  orders  produce? — 4S5.  Wh"t 
are  the  various  sources  of  electricity?  How  is  it  distinguished  from  other  forces? 
"Why  more  valuable  to  the  Chemist  ? 

22 


THE    RELATIONS    SUBSISTING  523 


§  VIII.    Conclusion  of  the  Chemical  Forces. 

486.  The  Relations  subsisting-  among-  the  three  Chemical 
Forces,  Heat,  Lijht  and  Elasticity.  They  are  convertible, 
ail  probably  di3  to  ths  notion  of  the  molecules  of  bodies. 

It  is  evident  fro.n  what  has  been  already  said,  that  the  three 
Chemical  forces,  Heat,  Light  and  Electricity,  are  not  mde- 
pendent  of  each  other,  but  very  closely  related,  and  mutually 
convertible.  Tans  Heat,  when  accumulated  to  a  sufficient  de- 
gree in  bodies,  is  capable  of  producing  both  Light  and  P^lectric- 
ity  without  the  intervention  of  any  other  force.  Lig'.it  is  capa- 
ble of  producing  both  Heat  and  Electricity  not  directly,  but  by 
the  intervention  of  the  force  of  Chemical  affinity.  Electricity 
is  capable  %of  producing  Heat  and  Light  directly,  and  by  the 
rapid  magnetization  and  de-magnetization  of  an  iron  bar,  §  398, 
can  also  produce  both  Molecular  motion  and  Heat.  These  Forces 
are  all  capable  of  being  produced  by  the  force  of  Mechanical  mo- 
tion ;  and  it  is  thought  by  so.ne  can  always  be  traced  ba  -k  to 
their  origin,  in  Motion.  If  this  be  so,  they  are  all  due  to  one 
cause,  viz — Motion  of  the  molecules  of  bodies.  Thus  Heat,  it 
is  well  known,  can  be  produced  by  Motion,  and  every  kind  of 
Heat,  as  we  have  seen,  §  238,  p.  230,  even  the  Heat  of  combus- 
tion, is  susceptible  of  explanation  on  this  principle.  Light  can 
also  be  produced  directly  by  Motion,  as  is  proved  by  the  flash 
which  accompanies  the  collision  between  projectiles  and  the 
target,  §  243,  p.  216.  Electricity  can  also  be  produced  directly 
by  Motion,  as  is  proved  by  the  operation  of  the  ordinary  elec- 
trical machine  and  the  revolution  of  colls  in  front  of  the  poles 
of  a  magnet.  The  derivation  of  the  three  Chemical  Forces 
from  Motion,  and  their  mutual  convertibility  are  elegantly 
shown  by  the  magneto-electric  machines  of  Saxton  and  Page,  Figs. 
245,  247.  In  these  machines  coils  of  wound  wire  are  made  to 
revolve  by  means  of  mechanical  motion  in  front  of  the  poles  of 
powerful  magnets ;  by  this  revolution,  the  magnets  are  made  to 
generate  momentary  currents  of  Electricity ;  by  this  electricity, 
when  transmitted  through  carbon  points,  intense  Heat  and  Light 
are  produced,  and  chemical  decomposition  effected,  as  is  shown 
by  the  use  of  the  light  for  the  illumination  of  Light-houses, 
and  by  the  precipitation  of  the  metals  from  their  solution^  in 
the  various  processes  of  electrotyping  and  plating.  Thus  Mo- 

4Si.  How  can  it  he  shown  that  tho  chemical  Forces  are  convertible?  H"»w  can  they 
be  traced  back  to  Mechanic  «1  Motion?  Bv  whit  machines  c.iu  the  derivation  of  the 
chemical  forces  aud  their  convertibility  be  shown? 


524  AMONG   THE    CHEMICAL    FORCES. 

tion  may  be  converted  successively  into  all  the  Forces  and  be 
made  to  appear  as  Heat,  Light,  or  Electricity.  The  do  eness 
of  this  relation  is  conclusively  shown  by  the  following  elegant 
experiment  of  Mr.  Grove.  A  prepared  daguerreotype  plate 
of  silver  coated  with  Iodine  is  enclosed  in  a  box  filled  with  wa- 
ter, having  a  glass  front  with  a  shutter  over  it.  Between  this 
glass  and  the  plate  is  a  gridiron  of  silver  wire.  The  silver 
plate  is  connected  with  one  extremity  of  the  coil  of  a  dedicate 
galvanometer.  The  gridiron  of  silver  wire  is  connected  w!th 
one  end  of  the  helix  of  Breguet's  metallic  thermometer,  Fig. 
50.  The  other  extremities  of  the  galvanometer  and  the  ther- 
mometer, are  connected  by  a  wire,  and  the  galvanometer  needles 
are  brought  to  zero.  Thus  a  complete  galvanic  circuit  is  con- 
structed: the  prepared  daguerreotype  plate  is  the  battery  gene- 
rating plate  ;  the  silver  gridiron,  the  conducting  plate  ;  the  wa- 
ter in  the  box,  the  exciting  liquid,  and  the  wire  which  runs  to 
the  galvanometer,  thence  to  the  thermometer,  and  then  back  to 
the  silver  gridiron,  is  the  conducting  wire.  As  soon  as  the  shut- 
ter which  covers  the  glass  front  of  the  box  is  raided  and  a  beam 
of  day-light,  or  of  the  electric  light  or  of  the  oxy-hydrogen  blow- 
p:pe,  is  permitted  to  fall  upon  the  silver  plate,  the  needle  of 
the  galvanometer  begins  to  move,  and  the  index  of  the  metal- 
lic thermometer  to  turn,  showing  the  circulation  of  electric- 
ity, with  the  production  of  magnetism,  and  the  evolution  of 
heat.  Thus  Light  being  the  initiating  force,  we  get  chemi- 
cal action  on  the  plate,  electricity  circulating  through  the  wires, 
magnetism  in  the  galvanometer,  heat  in  the  thermometer,  and 
motion  in  the  needles. 

This  proce-s  sometimes  goes  on  upon  a  great  scale  in  the  ope- 
rations of  nature.  Thus  by  the  action  of  the  Light  of  the  Sim 
upon  the  leaves  of  plants,  the  carbonic  acid  which  they  inspire 
from  the  air  is  decomposed,  and  the  Carbon,  which  constitutes  a 
large  part  of  the  substance  of  plants,  set  free.  It  is  by  this 
process  that  the  Carbon  which  now  constitutes  the  vast  depots 
of  coal  buried  beneath  the  soil  has  been  withdrawn  from  the 
ancient  atmosphere  of  the  earth.  By  this  action  of  Light,  in 
virtue  of  which  this  Carbon  is  withdrawn  from  chemical  com- 
bination, an  equivalent  amount  of  chemical  force  is  created, 
and  the  liberated  carbon,  recornbining  with  the  oxygon  of  the 
air,  will  produce  an  equivalent  amount  of  Heat.  The  Heat  thus 
set  free  produces  by  its  effect  on  water,  an  equivalent  amount  of 

Describe  Mr.  Grove1*  experiment.  W!i-\f.  is  the  initiating  Force  in  this  experiment  ? 
In  what  operation  of  nature  is  this  process  carried  on  upon  a  large  scale  ?  jDescribe  this 
process. 


THE    EQUIVALENCY  .  525 

molecular  motion  resulting  in  the  formation  of  steam,  an-1  this 
in  turn  produces  a  definite  amount  of  mechanical  motion 
in  tli3  Steam-Engine,  which  if  applied  to  the  revolution  of  the 
coils  of  a  Magneto-electric  machine,  would  evolve  a  sufficient 
amount  of  electricity  to  set  free,  by  means  of  carbon  points,  an 
amount  of  Heat  and  Light,  provided  nothing  were  lost  in  these 
repeated  transfers,  exactly  equivalent  to  the  Heat  and  Light  of 
the  original  sunbeams  whose  active  agency  enabled  the  leave? 
to  decompose  the  carbonic  acid  of  the  atmosphere.  It  wa*, 
therefore,  not  without  reason  that  Mr.  Geo.  Stephenson,  th;3 
inventor  of  the  Locomotive,  ascribed  the  power  that  drove  it  to 
the  light  of  the  sun.  "  Can  you  tell  me,"  he  said  to  Dr.  Buck- 
land,  "  what  is  the  power  that  is  driving  that  train ? "  "I  sup- 
pose it  is  one  of  your  big  engines."  "  What  do  you  say  to  the 
light  of  the  sun  ?  "  "  How  can  that  be  ?  "  "  It  is  nothing  else  ; 
it  is  light  bottled  up  in  the  earth  for  tens  of  thousands  of  years, — • 
light  absorbed  by  plants  and  vegetables  being  necessary  for  the 
condensation  of  carbon  during  the  process  of  their  growth — 
and  now  after  being  buried  in  the  earth  for  long  ages  in  fields 
of  coal,  that  latent  light  is  again  brought  forth  and  liberated, 
nwle  to  work  as  in  that  locomotive  for  great  human  purposes.'* 

From  the  mutual  convertibility  of  these  three  Forces,  it  is 
evident  that,  when  any  one  of  them  disappears,  and  seems  to  be 
destroyed,  it  may  in  fact  only  be  undergoing  a  process  of  con- 
version into  one  of  the  other  two,  and  presently  re-appear  in  an- 
other form.  The  motion  of  a  rapidly  moving  ball  seems  to  be 
annihilated  by  strikfng  against  the  target,  but  in  reality  it  is  only 
converted  into  another  force,  viz.,  that  of  heat,  as  is  proved  by 
the  rise  of  temperature  both  in  the  ball  and  target.  Force,  there- 
fora,  disappears  in  one  form  to  re-appear  in  another.  And  not 
only  is  this  true,  but,  the  new  Fore0-  thus  produced  by  de-volu- 
tion out  of  another,  is  exactly  equivalent  in  amount  to  that  of 
the  Force  which  has  disappeared. 

487.  In  every  case  of  the  convertibility  of  the  Chemical 
Forces,  there  is  an  expenditure  of  the  original  Force,  and  a  re- 
duction of  its  strength  exactly  equivalent  to  that  of  the  new 
Farce  produced,  into  which  it  has  been  changed.  In  all  cases 
where  a  given  amount  of  force  is  in  action,  if  the  result  be  the 
production  of  a  second  force,  the  original  force  is  reduced  in 

State  Mr.  Stephenson "s  opinion  of  the  origin  of  the  power  driving  the  Locomotive. 
What  becomes  of  the  original  Force  in  all  cases  of  apparent  disappearance? — 487.  Is 
there  any  proportion  between  the  original  Force  and  the  new  one  into  which  it  is  con- 
verted ? 


526 


OF    THE    CHEMICAL 


strength  to  a  degree  exactly  proportioned  to  that  of  the  new 
force  called  into  being.  Thus  when  the  movement  of  a  defi- 
nite amount  of  galvanic  electricity  produces  a  development  of 
heat  in  a  conducting  wire,  the  amount  of  electricity  in  circula- 
tion is  diminished  to  a  degree  exactly  equal  to  the  amount  of 
heat  brought  into  action.  When  the  rapid  motion  of  a  wheel 
results  in  producing  great  heat  in  the  axle,  there  is  a  retarda- 
tion in  the  motion  of  the  wheel,  exactly  equivalent  to  the  de- 
gree of  heat  excited  in  the  axle. 

This  is  very  beautifully  and  conclusively  proved  by  the  ex- 
periment of  M.  Favre,  referred  to  in  §  360.  A  voltaic  bat- 
tery, and  an  electro-magnet  actuated  by  it,  were  placed  in 
two  adjacent  calorimeters  somewhat  similar  to  that  of  Lavoisier 
and  Laplace,  §  232,  and  the  heat  produced  in  a  given  time 
within  the  battery,  when  the  connection  with  the  electro-mag- 
net was  established,  ascertained :  the  electro-magnet  was  then 
made  to  raise  a  weight,  or  in  other  words  a  portion  of  the  pow- 
er of  the  battery  was  converted  into  motion,  and  the  amount  of 
heat  in  circulation  during  a  space  of  time  exactly  equal  to  the 
former  again  noted.  It  was  found  that  the  heat  within  the  batte- 
ry was  diminished  in  exact  proportion  to  the  amount  of  mechan- 
ical effect  exerted,  and  the  amount  of  heat  which  disappeared 

was  found  by  calcu- 

Fig.  269.  lation  to  be  exactly 

equal  to  the  amount 
of  heat  which  this 
mechanical  power 
thus  produced,  was 
capable  of  evolving, 
according  to  Joule's 
Law,  §25 4,  i.e,  a  de- 
finite amount  of  Heat 
had  been  resolved  in- 
to a  definite  amount 
of  mechanical  mo- 
tion, exactly  equal  to 
the  mechanical  mo- 
tion required  for  the 
production  of  an 
equal  amount  of  heat,  the  process  being  reversed. 


Motion  Converted  into  Heat. 


Describe  M.  Favre's  experiment  by  which  the  equivalence  of  the  new  Force  to  the 
original  Force  is  proved.    What  was  the  result  ? 


\ 

FORCES.  527 

The  same  fact  is  shown  with  equal  conclusiveness  by  an  ex- 
periment of  M.  Foucault ;  if  a  thin  circular  disc  of  copper  c,  Fig. 
269,  be  mounted  on  a  shaft  between  the  poles  of  a  powerful  elec- 
tro-magnet in  the  equatorial  axis,  it  can  be  made  to  revolve 
with  great  rapidity  by  means  of  the  multiplying  wheel  M,  so  long 
as  there  is  no  connection  between  the  electro-magnet  and  the 
battery,  and  this  movement  will  continue  for  some  time  after 
the  propelling  force  is  withdrawn,  from  the  momentum  it  has 
acquired.  If,  at  this  moment,  the  connection  with  the  battery 
be  established  so  that  the  electro-magnet  becomes  powerfully 
magnetized,  the  motion  of  the  disc  is  checked  by  the  dia-mag- 
netic  action,  §  39 2,  exerted  upon  it,  and  by  the  secondary  electrical 
currents  §  447,  induced  within  it  by  the  action  of  the  electro- 
magnet, and  it  becomes  exceedingly  difficult  to  turn  it ;  at  the 
same  time  the  temperature  of  the  disc  instantly  rises ;  in  other 
words,  the  force  applied  to  the  wheel  remaining  the  same  as 
before,  and  not  being  able  to  expend  itself  in  the  production  of 
motion,  is  converted  in  part  into  heat,  and  the  disc  at  once  becomes 
very  hot ;  in  one  experiment  the  temperature  ro.-e  from  almost 
55°  F.  to  165°.  It  has  been  stated,  §  470*  p.  497,  that  when 
an  armature  carrying  a  coil  is  made  to  revolve  between  the 
poles  of  an  electro-magnet  it  beco:nes  much  more  difficult  to 
turn  it,  and  its  speed  is  greatly  reduced  the  instant  the  battery 
current  is  made  to  circulate  through  the  electro-magnet :  by  en- 
closing such  an  armature  in  a  glass  tube  filled  with  water,  and 
causing  the  whole  to  revolve  between  the  poles  of  the  electro- 
magnet, Mr.  Joule  has  endeavored  to  estimate  the  amount  of 
heat  into  which  a  portion  of  the  mechanical  force  has  been  con- 
verted, by  the  rise  of  a  thermometer  placed  in  the  water. 

In  like  manner,  if  the  poles  of  a  galvanic  battery  be  joined 
by  a  thin  platinum  wire,  the  wire  will  be  ignited  and  a  certain 
amount  of  chemical  action  will  take  place  in  the  battery,  a  defi- 
nite quantity  of  zinc  being  dissolved,  and  of  Hydrogen  set  free 
in  a  given  time,  resulting  in  the  production  of  a  definite  amount 
of  electricity  circulating  through  the  wire,  of  which  a  portion 
is  converted  into  heat.  If  now,  the  platinum  wire  be  placed  in 
water,  its  conducting  power  will  be  increased  in  consequence  of 
the  diminution  of  resistance  by  the  reduction  of  temperature, 
a  larger  amount  of  the  electrical  force  will  be  converted  into 
heat  than  before,  and  the  chemical  action  on  the  generating 
plates  within  the  battery  will  be  found,  on  examination,  to  have 
been  correspondingly  augmented.  If  the  experiment  be  re- 
Describe  M  Foucault's  experiment.  If  a  portion  of  the  power  of  the  battery  be  ex- 
pended in  the  production  of  Hf"»t  what  effect  is  produced  upon  its  chemical  power? 


528  THE    INDESTRUCTIBILITY  wV 

versed  and  the  wire  be  placed  in  the  flame  of  a  spirit  lamp,  by 
•which  its  conducting  power  for  heat  is  diminished,  §  333,  the 
chemical  action  is  correspondingly  reduced. 

These  instances  might  be  multiplied  indefinitely,  and  it  is 
now  a  generally  received  truth  that  when  one  Force  is  convert- 
ed into  another,  the  strength  of  the  original  Force  is  propor- 
tionably  reduced,  and  that  the  strength  of  the  new  Force  is  ex- 
actly equivalent  to  the  diminution  in  the  strength  of  the  Force 
from  which  it  has  been  derived. 

488.  The  Convertibility  and  Equivalency  of  Force,  true  of 
all  the  Forces  which  act  on  Matter.     Not  only  is  the  converti- 
bility and  equivalency  of  Force  true  of   the    Forces,   Heat, 
Light  and  Electricity,  but  also,  it  is  thought,  of  the  other  Forces 
which  act  on  Matter,  viz :  the  attraction  of  Gravitation  and  the 
attraction  of  Chemical  Affinity.     This  seems  to  be  pretty  con- 
clusively proved  in  the  case  of  Chemical  Affinity  fi  om  the  in- 
stances cited  above,  in  which  the  amount  of  Chemical  Force 
in  action  in  the  battery  is  increased  or  diminished  in  proportion 
to  the  increase  and  diminution  of  the  strength  of  the  Forces  to 
which  it  gives  rise.     But  the  convertibility  of  Gravity  into  new 
Forces,  and  of  other  Forces  into  Gravity,  has  not  as  yet  been 
so  conclusively  shown.     This  is  a  step  wrhich  yet  remains  to  be 
taken.     At  present  we  may  be  justified,  perhaps,  in  regarding 
Gravity  and  Chemical  attraction,  i.  e.,the  Force  of  attraction 
which  masses  of  inert  matter  exert  reciprocally  upon  each  other, 
by  which  they  are  drawn  together;  and  the  Force  of  attraction 
which  the  atoms  of  different  elements  and  the  more  simple 
chemical  compounds  exert  upon  each  other,  by  which  they  are 
bound  together,  and  united  into  the  various  compound  substances 
which  we  see  around  us, — as  Primary  Forces  impressed  upon  all 
kinds  of  matter,  no  portion  being  exempt,  and  the  latter  made 
capable  of  modification  ?nd  control,  from  the  action  of  the  Sec- 
ond  ry  Forces, — Heat,   Light  and  Electricity,  which  have  just 
been  described. 

489.  The  Indestructibility  and  Conservation  of  Force; 
the  Correlation  of  the  Forces.     It    results  as    a   consequence, 
from  this  principle,  that,  when  a  new  force  seems  to  be  devel- 
oped by  the  action  of  one  formerly  existing,  there  is  no  crea- 
tion of  Force  on  the  one  hand,  and  no  destruction  of  Force  on 
the  other,  but  merely  a  conversion  of  one  Force  into  another. 

488.  Is  the  convertibility  and  equivalency  of  Force  true  of  all  the  Forces  ?  What  is 
sal!  in  regard  to  th«  attraction  of  gravitation,  and  of  chemical  affinity  ? — 489.  What 
consequence  results  from  this  principle  ? 


AND    CONSERVATION    OF    FORCE  529 

Force  is  therefore  believed  to  be  as  indestructible  as  Matter. 
By  this  expression  it  is  not  meant  that  either  Force  or  Matter 
are  absolutely  incapable  of  destruction,  but  simply  that  in  fact, 
neither  of  them  are  destroyed  in  the  various  transmutalioris 
which  they  undergo,  but  are  merely  changed  from  on^  foi'm  to 
another.  The  sum  total  of  Force  in  the  U.iiver=e,  as  well  as 
the  sum  total  of  Matter  always  remains  the  same,  but  both 
may  be  transmuted  from  one  form  into  many  others.  There 
is  never  any  fresh  creation  of  either. 

This  is  what  is  signified  by  the  Term,  now  very  generally  in- 
troduced into  Science,  the  Conservation  of  Force,  i.  e.,  no  Force 
is  ever  destroyed  ;  and  the  convertibility  of  the  various  kinds  of 
Force  into  each  other,  in  virtue  of  which  this  Conservation  of 
Force  is  maintained,  is  of;en  designated  by  the  term,  Co-relation, 
or  Correlation  of  the  Forces.  These  terms  were  first  intro- 
duced, and  the  truths  wlnVh  they  were  designed  to  express, 
were  first  advoca!ed  in  England  by  Mr.  Grove,  the  distin- 
guished inventor  of  the  Nitric  acid  Ba:tery,  in  1842.  The 
same  general  doL-trine  of  the  mutual  relations  of  the  Forces, 
was  put  forth  about  the  same  time  by  Mr.  Joule,  in  England, 
no:ed  for  his  determination  of  the  mechanical  equivalent  of 
Heat;  by  Mayer,  in  Germany,  and  Colding,  in  Denmark. 
The  idea  that  Heat  and  Motion  are  two  different  forms  of 
tha  same  Force,  and  mutually  convertible,  wa*  first  advanced 
by  the  celebrated  Montgolh'er  about  1800.  The  same  idea 
was  set  forth  independently  by  M.  Carnot,  in  1824,  and 
worked  out  more  elaborately  in  his  bouk  upon  "  Tne  Motive 
Power  of  Heat."  Mr.  Grove  conceived  the  same  idea  at  a  some- 
what later  period,  independent  of  both  the  former,  and  was 
the  first  to  treat  the  subject  in  a  systematic  manner,  and  give 
it  a  scientific  form.  It  is  one  of  ihe  most  important  advances 
made  in  Physical  Philo;ophy  in  the  present  century,  and  is  the 
line  upon  which  research  is  now  rapidly  progressing.  Tne  mo-t 
important  works  upon  the  subject  are,  Grove,  on  the  "Correla- 
tion of  the  Physical  Forces"  and  Tyndall,  on  "Heat  Considered 
as  a  Mode  of  Motion" 

£90.  Heat  and  Electricity  the  chief  Ag-ents  used  by  the 
Cheraist,  in  his  investigations.  Tha  Isamp  and  the  Galvanic 
Uaitevy  his  chief  Instruments.  Or'  the  three  Chemir-al  Forces, 
Heat  and  Electricity  are  the  most  important  to  the  chem- 
ist in  canying  on  his  researches  into  the  composition  of 

What  is  meant  by  the  terms  Indestructibility  and  Conservation  of  Force?     How  te 
this  Conservation  maintained  ?     What  is  meant  by  the  term  Correlation  of  th 
Who  introduced  these  terms  ?    Give  the  history  of  the  progress  of  these  ideas. 


530  ^CONCLUSION. 

Matter,  and  in  making  the  modifications  which  he  desires,  in 
the  attraction  of  Cliemical  Affinity.  While  Light  is  extensively 
employed  by  Nature  in  carrying  on  some  of  her  most  remark- 
able chemical  transmutations  especially  in  the  de-oxida'ion  of 
Carbonic  acid  by  the  leaves  of  Plants,  and  generally  in  the 
chemistry  of  the  vegetable  kingdom,  by  the  Chemist  Light  is 
hardly  used  in  any  process  except  that  of  taking  Photographic 
pictures,  and  occasionally  for  effecting  a  few  remarkable  com- 
binations, such  as  that  of  Chlorine  and  Hydrogen  for  the  pro- 
duction of  Chloro-Hydric  acid. 

The  chief  instruments  which  the  chemist  employs  for  the  de- 
velopment and  application  of  his  two  Principal  Forces,  are,  for 
Heat,  the  Lamp,  the  Wind  Furnace,  the  Gas-jet,  the  Oxy-IIy- 
drogen  Blow-pipe,  the  common  Blow  pipe, — all  depending  upon 
the  process  of  Combustion, — and  the  carbon  points  of  the  Bat- 
tery:— for  Electricity,  the  Galvanic  Battery,  the.  Magneto-elec- 
tric machine,  the  Thermo-electric  Battery,  and  Ruhinkorffs  coil. 
He  also  employs  the  carbon  points  of  the  battery,  and  the 
terminals  of  Iluhmkorff's  coil,  for  the  production  of  the  most 
intense  heat  known  to  man,  in  his  researches  into  the  composi- 
tion of  matter  by  Spectrum  analysis.  The  Lamp  and  the  Fur- 
nace were  known  to  the  Alchemists ;  all  the  others,  from  the 
Galvanic  battery  down,  have  been  the  fruit  of  the  scientific  and 
inventive  genius  of  the  present  century. 

491.  The  Conclusion  of  the  Chemical  Forces.  Thus  we 
have  briefly  con-idered  the  nature  and  principal  properties  of  the 
three  active  Agents  or  Forces,  by  which  the  attraction  of 
Chemical  Affinity  is  controlled  and  modified,  and  described  the 
most  important  instruments  employed  in  their  application.  We 
are  now  prepared  to  make  this  application  and  to  enter  upon 
the  examination  of  the  chemical  character  of  the  elements  of 
which  the  various  kinds  of  matter  are  composed,  and  the  nature 
and  laws  of  the  Force  of  Affinity  by  which  they  are  bound 
together.  This  constitives  the  subject  matter  of  Chemistry 
proper,  and  will  be  reserved  for  a  subsequent  volume  devoted 
to  the  consideration  qf  the  chemical  properties  and  relations 
of  the  various  k:nds  of  Matter,  Inorganic  and  Organic,  of  which 
the  Universe  con-i  ts. 


49*.  What  are  the  chief  Agents  used  by  the  Ch«*W*t?  What  use  does  he  make  of 
Light?  What  use  is  made  of  Light  in  Natuve?  What  are  the  chief  instruments  em- 
plo.ed  by  the  Chemist  for  heat  ?  for  elecrricitv  ?  Which  of  them  were  ki.own  to  the 
Alchemists?— 401,  Wbea  were  toe  others  introduced  ?  State  the  conclusion  of  the 


EXPERIMENTS    ON    GALVANISM.  531 


Experiments:    Galvanic  Electricity,  Electro-Magnetism,  and 
.Magneto-Electricity. 

1.  The  Battery.    A  battery  of  12  elements  of  Grove  or  6  of  Bunsen,  will  be  large 
enough  to  exhibit  nearly  all  the  effects  of  Galvanic  Electricity,     The  zinc  plates  should 
be  well  amalgamated  by  dipping  them  first  in  dilute  chloro-hydric  acid,  until  they  are 
thoroughly  cleansed,  and  then  into  a  cup  of  mercury, 

2.  The  charge  for  this  battery  is  1  measure  of  sulphuric  acid  to  6  or  8  of  water,  mixed, 
and  allowed  to  cool.     In  case  any  of  the  zincs  effervesce  in  the  acid,  they  must  be  taken 
out  and  dipped  anew  in  the  mercury.     The  porous  clay  cups  should  be  filled  with  the 
strongest  Nitric  acid  which  can  be  procured. 

3.  Bi-Chromate   of  Potash  in  solution,   is  often  used   in  place  of  Nitric  acid  in 
Grove's  and  Bunsen's  batteries,  for  the  purpose  of  escaping  the  nitrous  acid  fumes, 
•which  are  evolved  in  large  quantity  when  Nitric  acid  is  decomposed,     1'our  parts  of  Bj- 
Chromate  of  Potash  are  dissolved  in  eighteen  parts  of  water,  and  mixed  with  four  p  irta 
of  Sulphuric  acid.     The  Hydrogen  which  penetrates  into  the  porous  cup,  unites  with  a 
part  of  the  Oxygen  of  the  Chromic  acid,  and  reduces  it  to  the  state  of  Oxide  of  Chro- 
mium, which  remains  dissolved  in  the  Nitric  acid  ;  the  strength  of  the  battery  however 
is  much  less  than  when  Nitric  acid  is  employed,  owing  to  the  increased  resistance. 

4.  The  Connections.     The  poles  may  be  connected  by  means  of  copper  wires,  well  an- 
nealed, so  as  to  be  readily  twisted  and  bent,     The  ends  pf  these  wires  should  be  bright- 
ened  with  a  file,  or  amalgamated  by  acid  and  mercury.     The  tips  of  the  screws  connect- 
ing them  with  the  battery,  should  also  be  brightened  with  a  file.    This  is  a  precaution 
of  greit  importance,  as  the  full  power  of  a  battery  can  not  be  brought  out  if  the  connec- 
tions be  oxidated-     The  battery  should,  if  possible,  be  so  constructed  as  to  admit  of  the 
zinc  plates  being  all  connected  together  by  binding  cups,  so  as  to  form  pne  zinc  plate, 
and  the  platinum  plates  so  as  to  form  one  platinum  plate,  as  in  Fig.  158 ;  or,  of  being 
arranged  alternately,  as  in  Fig.  157.     The  former  arrangement  should  be  adopted  for  ex- 
periineuts  upon  the  heating  and  magnetic  effects  of  the  battery,  and  the  latter  for  expert- 
meats  upon  its  chemical  effect. 

5.  Position.     The  battery  must  be   placed  in  a  draught  of  air,  so  that  the  noxious 
nitrous  acid  fumes  may  not  be  permitted  to  escape  into  the  room. 

6.  The  Slip  hate  of  Copper  Battery.     The  charge  for  this  battery  is  a  solu- 
tion of  the  Sulphate  of  Copper  in  water  ;  a  saturated  solution  of  this  salt  must  first  be 
made,  and  to  this  added  an  equal  quantity  of  water.     A  pint  of  water  at  the  ordinary 
teinperature  is  capable  of  dissolving  one-fourth  of  a  pound  of  the  salt,  so  that  the  half- 
satur  ited  solution  will  contain  about  two  ounces  of  the  salt  to  the  pint.    The  coating 
of  oxide  of  copper  which  is  formed  upon  the  zinc  plate,  should  always  be  removed  imme- 
diately after  using,  by  means  of  the  card  brush  and  plenty  of  water  ;  if  this  is  neglected 
tlie  zino  becomes  covered  with  a  hard  coating  which  can  only  be  removed  by  scraping 
or  fi'ing.     The  deposit  of  copper  must  also  be  removed  from  time  to  time.     The  zinc 
plate  must  always  be  taken  out  of  the  solution  when  the  battery  is  not  in  action,  but 
the  solution  itself  may  remain  in  the  copper  cylinder,  as  it  has  no  chemical  action  upon 
it,  but  tends  to  keep  its  surface  in  good  condition.     When  the  solution  in  exhausted,  it 
is  best  not  to  attempt  to  renew  its  power  by  adding  a  fresh  quantity  of  the  salt ;  it 
should  be  thrown  away,  and  a  new  solution  prepared. 

7.  Diaiell's  Battery.     The  charge  for  this  battery  is  a  saturated  solution  of  Sul- 
phate of  Copper  acidulated  with  an  eighth  of  its  bulk  of  Sulphuric  Acid,  and  placed  in 
the  outer  cup:  the  solution  is  kept  saturated  by  crystals  of  the  same  salt  placed  in  the 
colander  c,  Fig.  151,    The  inner  porous  cup  is  charged  with  a  mixture  of  one  measure 
of  Sulphuric  Acid,  and  seven  measures  of  water. 

8.  Smsa's  Battery.     The  charge  for  this  battery  is  one  measure  of  Sulphnria 
Acid  to  six  measures  of  water :  the  strength  of  the  charge  may  be  increased  by  the  addi- 
tion of  bulphunc  Acid,  until  the  proportion  is  reached  of  one  of  Acid  to  four  of  Water. 

9.  Tiia  Qis  Battery.     The  usual  charge  for  Grove's  gas  battery,  Pis*.  144,  is 
Oxygen  and  Hydrogen  m  the  two  tubes,  dipping  into  a  vessel  of  water  acidulated  with 
SulpHime  acid.     Jther  gases  however  may  be  employed.     Chlorine  may  he  placed  in  one 
tube,  fi'id  Hydrogen  in  the  other,  and  connected  bv  acidulated  water :  the  Chlorine  nth-arts 
the  H/drogen  of  the  water,  forming  Chloro-hvdric  acid  in  the  Chlorine  tube,  find  the 
Ox/gea  which  is  set  fn>e  unite*  with  the  Hvdrogen  to  form  water  in  the  Hvdro-ren  tube. 
Oxygen  may  be  placed  in  one  tube,  and  Nitrogen  containing  a  piece  of  Phosphorus  in 
th«  other:  the  Phosphorus  attracts  the  Oxygen  of  the  water  and  forms  Phosphoric 
^cid  in  one  tube,  while  the  Hvdrogen  which  is  s=<>t  free  wnites  with  the  Oxvgen  of  the 
other  tube  to  form  water.     With  50  pairs  a  decidedlv  painfnl  shock  ran  be  given  to  a 
Bjngle  person :  the  wedle  of  a  galvanometer  will  be  powerfully  affected ;  a  brilliant 


532  HEATING  AND    ILLUMINATING   EFFECTS.' 

spark  projected  between  carbon  points  :  Iodide  of  Potassium  and  acidulated  water  may 
be  decomposed,  and  gas  enough  set  free  i»  the  last  case  to  be  collected  and  detonated. 
Twenty-six  pairs  were  found  to  be  the  smallest  number  that  would  decompose  wa- 
ter, but  four  pairs  will  decompose  Iodide  of  Potassium.  A  gold  leaf  electroscope  will  be 
sensibly  affected. 

1 0.  That  chemical  action  is  the  source  of  the  electrical  current,  may  be  shown  by  dip- 
p'ng  an  unamalgamated  zinc  plate  into  a  mixture  of  sulphuric  aci<l  and  water ;  bubbles 
of  hydrogen  will  be  formed  on  its  surface,  and  rise  through  the  water ;  the  zinc  will  at 
the  same  time  be  oxidated.     Introduce  a  copper  plate,  and  establish  a  metallic  connec- 
tion between  it  and  the  zinc ;  the  bubbles  will  then  cease  to  be  discharged  upon  the 
zinc,  and  will  form  upon  the  copper.    If  the  plates  be  large,  the  wires  com  ected  with 
them  will,  when  brought  near  each  other,  emit  a  spark,  grow  perceptibly  warm  to  the 
touch,  and  deflect  the  magnetic  needle.    The  source  of  the  electrical  current  is  evidently 
the  decomposition  of  the  water  by  the  zinc.    If  several  pairs  of  such  plates  be  united, 
the  copper  of  one  being  attached  to  the  zinc  of  the  next,  a  powerful  battery  n*ay  easily 
be  constructed. 

1 1.  If  the  zinc  be  well  amalgamated  no  effect  will  be  produced  when  it  is  dipped  into 
the  acidulated  water,  and  no  bubbles  of  hydrogen  will  be  formed  upon  its  surface ;  but 
the  instant  a  connection  with  the  conducting  plate  is  formed,  by  means  of  a  wire,  bubr 
bles  of  hydrogen  will  be  abundantly  discharged  upon  the  copper,  as  before. 

12.  Heating  Effects.     Wind  a  fine  copper    connecting  wire  several  times  around 
the  bulb  of  an  air  thermometer,  Fig.  45,  and  the  liquid  will  rise  rapidly  in  the  stem. 
Touch  the  wire,  and  it  will  be  found  to  be  very  hot. 

1 3.  Dip  the  two  poles  into  water,  or  cause  the  current  to  circulate  through  a  coil  of  fine 
copper  wire,  placed  in  a  vessel  of  water  or  mercury,  and  the  temperature  of  the  liquid 
will  be  found  to  rise  rapidly. 

14.  Stretch  a  fine  platinum  wire,  three  or  four  yards  in  length,  between  two  fixed 
points,  and  transmit  the  voltaic  current,  it  will  become  first  red,  and  then  whi:e  hot ;  if 
the  wire  be  shortened,  the  effect  will  increase,  until  finally  it  will  melt  and  drop  in  glob- 
ules. 

15.  Try  the  same  experiment  with  fine  steel,  iron  and  copper  wire. 

16.  Construct  a  chain  of  alternate  links  of  silver  and  platinum  wire,  and  transmit  tb.6 
current ;  the  platinum  links  will  glow  brightly,  while  the  silver  will  remain  entirely  ob- 
scure. 

17.  Ignite  a  portion  of  a  platinum   wire,   which  has   been  made  red  hot  by  the 
passage  of  the  current,  in  the  flame  of  a  spirit  lamp,  and  the  brightness  of  the  wire  will 
sensibly  decline,  showing  the  diminution  of  the  current  produced  by  the  ignition  of  the 
metal  at  one  point,  and  the  consequent  increased  resistance. 

18.  If  a  loop  of  the  same  wire  be  cooled  by  immersion  in  water,  the  opposite  effect 
is  produced,  in  consequence  of  the  diminution  of  resistance  by  the  reduction  of  tempe- 
rature, thus  enabling  a  larger  quantity  of  electricity  to  traverse  the  wire,  and  the  me- 
tal will  thus  be  raised  to  a  white  heat,  almost  approaching  the  point  of  fusion. 

19.  The  burning  of  the  different  metallic  foils  may  be  effected  by  attaching  a  polished 
metallic  plate,  about  3£  inches  broad,  by  12  inches  long,  to  the  positive  wire,  and  inclin- 
ing the  plate  upon  any  convenient  support,  at  an  angle  of  45°  ;  then  attach  the  metallic 
foil  to  be  burned  to  the  negative  wire,  and  bring  it  into  contact  with  the  plate,  taking 
care  to  change  its  position  continually,  so  as  to  make  it  touch  fresh  surfaces ;  defla- 
gration will  immediately   take  place ;  gold  leaf  will  burn  with  a  bluish   white  light, 
crumbling  into  a  dark  brown  oxide ;  silver,  with  greenish  light ;  copper,  a  bluish  white ; 
lead,  purple  ;  zinc,  a  brilliant  white,  inclining  to  blue,  and  fringed  with  red. 

20.  Pour  mercury  into  a  small  glass  or  iron  cup.  and  connect  with  the  negative  pole 
of  the  battery,  then  fill  the  cup  with  copper,  silver,  or  gold  leaf,  and  touch  the  foil  with 
a  platinum  wire  attached  to  the  positive  pole ;  the  foil  will  burn  rapidly. 

21.  Attach  a  steel  watch  spring  to  the  positive  wire,  and  apply  it  to  the  surface  of 
tnercurv  connected  with  the  negative  pole,  as  in  the  last  case ;  the  watch  spring  will  give 
forth  a  shower  of  sparks:  try  the  point  of  a  file,  an  iron  nail,  fine  iron  wire,  zinc,  tin, 
lefid   copper,  in  like  numnGr.  . 

22.  Attach  a  broad  piece  of  charcoal  to  the  negative  wire,  and  bring  down  upon  it 
wires  of  different  metals,  attached  to  the  positive  pole ;  they  will  all  burn  in  like  man- 

n<*3.  Attnch  silver  leaf  to  the  negative  pole  under  alcohol,  and  apply  the  positive  pole ; 
inflammation  of  the  silver  will  take  place. 

24.  Try  the  effect  of  the  two  poles  upon  ether,  alcohol,  spirits  of  turpentine,  naptha, 

25.  Illuminating  Effects.     Attach  a  piece  of  gas-carbon,  filed  down  carefully 
to  a  fine  point,  to  each  wire  of  the  battery,  by  means  of  fine  copper  wire  tightly  bound 
7f  the  gas-carbon  can  not  be  procured,  take  pieces  of  box-wood,  or  hgnum-vitae.  cover 
.them  with  sand,  in  a  crucible,  and  expose  them  to  an  intense  furnace  heat  for  a  "hour, 
then  cool  suddenly  by  turning  out  upon  an  iron  plate,  or  by  plunging  them,  while  red- 


EXPERIMENTS    ON    GALVANISM.  533 

Jiot,  into  mercury,  or  into  water ;  bring  the  points  near  each  other,  and  an  intensely 
brilliant  flash  will  be  produced ;  draw  them  slowly  1  10th  of  an  inch  apart,  and  a  splen- 
did arc  of  name  will  be  formed.  The  effect  will  be  increased  if  the  positive  po.e  be  up- 
permost, as  in  Fig.  159. 

23.  Perform  the  same  experiment  underwater;  the  light  will  still  be  produced,  but 
with  diminished  splendor,  and  at  the  same  time  the  water  will  be  rapidly  decomposed. 

2  7.  Perform  the  same  experiment  in  an  exhausted  receiver.  Fig.  161 :  an  equally 
brilliant  effect  will  follow,  and  the  points  may  be  separated  to  a  greater  distance. 

23.  Apply  a  powerful  magnet  to  the  flame,  and  it  will  be  repelled,  assuming  an  equa- 
torial position :  by  holding  the  magnet  in  a  certain  position  the  flame  ma>  be  made  to 
revolve  accompanied  at  the  same  time  by  a  loud  sound,  Figs.  253,  254.  255,  256. 

23.  Observe  that  the  positive  pole  wears  away,  while  the  negative  increases  in  length. 

30.  With  Duboscq's  electric  lamp,  Fig.  161),  the  image  of  tiie  points  may  be  thrown 
upon  a  screen,  and  the  process  of  transport  very  plainly  seen. 

31.  If  the  carbon  poles  be  arranged  vertically,  as  in  Fig.  159,  and  the  negative  point 
be  replaced  by  a  carbon  cup,  on  which  small  bits  of  the  different  metals  are  placed,  they 
will  burn  with  great  brilliancy,  and  the  emission  of  their  characteristic  colors. 

32.  If  the  negative  carbon  cup  be  filled  with  mercury,  and  a  piece  of  moistened  pot- 
ash be  placed  upon  it,  the  potash  will  be  decomposed,  and  the  metal  potassium  set  free, 
forming  an  amalgam  with  the  mercury,  from  which  it  may  be  obtained  by  distillation. 

33.  If  mercury  be  placed  in  a  small  iron  cup  connected  with  the  positive  po  e  of  the 
battery,  and  be  allowed  to  trickle  in  a  very  fine  stream,  through  a  minute  aperture  into 
a  lower  iron  vessel  connected  with  the  negative  pole,  at  the  moment  of  contact  between 
the  globules  of  mercury  falling  from  the  upper  cistern  and  the  lower  cup,  the  mercury  is 
heated  to  a  white  heat,  and  produces  a  dazzling  white   light.     This  is  a  splendid  experi- 
ment. 

34.  Chemusal  Effects.    Decomposition  of  Water.     The  poles,  in  this  case,  should 
be  made  of  platinum,  and  inserted  from  belo-.v  into  inverted  glass  tubes,  closed  at  the  up- 
per end  Fig.  162.     The  water  should  be  acidulated  with  sulphuric  acid,— 1  part  of  acid  to 
15  parM  of  water, — in  order  to  increase  its  conducting  po  .vcr.     The  hvdrogen  will  collect  in 
the  negative  tube,  the  oxygen  in  the  positive  tube ;  the  former  in  double  the  quantity  of 
the   Latter.      This   experiment   may    be  performed    with    the  U  tube,   Fig.    164,  which 
must  be  filled  with  acidulated  water;  the  poles  mast  be  thrust  far  down  into  the  tubes, 
so  as  nearly  to  touch,  passing  through  corks  at  tieir  mouths :  a  bent  glass  tube  may  be 
used  to  convey  the  gas  from  the  oxygen  end;  and  the  hydrogen  may  be  burned    as  it  is 
formed,  from  the  extremity  of  another  glass  tube,  drawn  down  to  a  very  fine  bore      This 
makes  a  very  beautiful  experiment. 

35.  Pass  the  galvanic  current,  in  an  apparatus  similar  to  the  last,  through  ch'oro-hy- 
dric  acid.     Hydrogen  will  be  discharged  in  the  negitive  tube,  and  may  be  burned  from 
a  fine  orifice;  chlorine  will  be  discharged  in  fie  positive  tube,  and  may  be  recognized  bv 
its  olor,  and  its  bleaching  effect  upon  solution  of  sulphate  of  indigo,  whe.i  poured  into 
the  tube ;  also,  by  its  green  color. 

35.  Repeat  the  same  experiment,  substituting  tincture  of  litmus,  of  violets,  or  purple 
cabbage,  for  the  indigo;  tne/  will  at  first  be  turnel  red  by  the  acid,  and  then  will  be 
quickly  bleached  as  the  chlorine  is  disengaged,  lor  the  preparation  of  tincture  of  pur- 
ple cabbage,  see  Expt  16.  p.  77. 

37.  Pass  the  current  through  a  stron*  solution  of  common  salt — chloride  of  sodium, 
colored  blue  in  both  tubes  by  tiuf  ture  of  cabbage ;  chlorine  will  be  discharged  in  the 
positive  tube,  and  almost  immediately  destroy  the  blue  co  or.  and  sodium  will  be  set  free 
in  the  negative  tube;  this  will  be  at  once  converted  into  soda  by  decomposing  the  water, 
and  change  the  blue  color  to  a  brig'it  green. 

33.  Pass  the  current  throug'i  aqua  :>mmonia,  in  a  similar  apparatus.  Hydrogen  will 
be  discharged  in  the  negative  tube,  and  may  te  ,'et  on  fire,  as  in  Expt.  £4,  and  nitiopcn 
•will  be  set  free  in  the  positive  tub»,  as  may  be  shown  by  its  extirguifbJng  a  lighted  t;;j>er. 

39.  Pass  the  current  through  ni  ric  acid,  in  a  similar  tube.     Oxygen  will  be  discharged 
in  the  positive  tube,  as  may  be  shown  by  its  effect  on  a  lighted  taper,  and  ret',  nitrous 
acid  fumes  in  the  negative  tube      If  a  candle,  having  its  wirk  glowing  red-hot,  but  not 
ligited,  be  introduced  into  the  oxygen  tube,  it  will  I  e  re-lighted  :  a'uo  paper. 

40.  Pass  the  current  through  a  strong  solution  of  iodide  of  potassium  :  into  the  posi- 
tive tube  introduce  a  few  drops  of  solution  of  starch,  and  into  the  negative  some  tireture 
of  cabbage ;  iodine  will  be  set  free  at  the  positive  pole,  and  its  presence  shown  by  tinging 
the  starch  a  deep  blue,  and  potassium  set  free  at  the  negative  pole,  which  will  at  once 
be  converted  into  potash  by  abstracting  ox_ygen  from  the  water,  and  its  presence  indica- 
ted by  turning  the  vegetable  blue  to  green. 

41.  Pass  the  current  through  a  solution  of  sulphate  of  soda,  in  the  U  tube,  tinged  by 
tincture  of  cabbage  ;  the  salt  wil    be  decomposed  into  sulph'uric  acid  and  soda  ;  the  acid 
appearing  at  the  positive  pole,  and  turning  the  blue  to  red,  and  the  soda  at  the  negative 
pole,  changing  the  blue  to  green  ;  if  the  platinum  wires  be  removed,  and  the  contents 
of  the  two  branches  of  the  tube  shaken  together,  the  acid  and  the  soda  will  again  unite, 
the  red  will  neutralize  the  green,  and  the  blue  color  will  be  restored. 


534  CHEMICAL    EFFECTS.  s 

42.  Pass  the  current  through  a  solution  of  nitrate  of  potash,  colored  blue  by  the  tine* 
ture  of  cabbage ;  ni'ric  acid  will  be  set  free  at  the  positive  pole,  shown  by  the  red  color, 
and  potash  at  the  negative  pole,  shown  by  the  change  of  blue  to  green. 

43.  Pass  the  current  through  a  solution  of  chloio  hydrate  of  ammonia  (sal  ammo- 
niac )  in  the  U  tube,  colored  blue  by  tincture  of  cabbr.ge ;  chlorine  will  be  set  free  at 
the  positive  po'e,  discharging  the  blue  color  altogether,  and  ammonia  at  the  negative  pole, 
changing  the  blue  to  green. 

4*.  Pass  the  current  through  a  solution  of  carbonate  of  potash,  colored  blue  by  tinc- 
ture of  cabbage ;  carbonic  acid  will  be  discharged  at  the  positive  pole,  with  effervescence, 
slightly  reddening  the  blue  tincture,  and  potash  at  the  negative  pole,  turning  (he  blue  to 
a  deep  green. 

*D.  Try  the  same  experiment  with  a  solution  of  carbonate  of  soda:  carbonic  acid 
•will  be  set  free  at  the  positive  pole,  and  soda  ut  the  negative. 

46.  Try  the  same  experiment  with  solution  of  nitrate  of  lime;  nitric  acid  will  appear 
at  the  positive  pole,  and  lime  at  the  negative. 

47.  Kepeat  the  same  experiment  with  the  solution  of  acetate  of  lead ;  acetic  acid  will 
be  set  free  at  the  positive  pole,  reddening  a  vegetable  blue,  and  pure  lead  at  the  negative 
pole. 

48.  Repeat  the  same  experiment  with  the  solution  of  nitrate  of  silver;  nitric  acid  will 
be  set  tree  at  the  positive  pole,  and  metallic  silver  at  the  negative. 

49.  Repeat  the  same  experiment  with  the  solution  of  chloro -hydrate  of  tin ;  the  acid 
will  be  set  free  at  the  positive  pole,  and  tin  deposited  at  the  negative  pole. 

60.  Repeat  the  same  experiment  with  the  solution  of  nitrate  ol  mercury ;  the  acid 
•will  be  set  free  at  the  positive  pole,  and  the  mercury  at  the  negative. 

61.  Pass  the  current  through  a  solution  of  chloride  of  calcium,  colored  blue  by  tinc- 
ture of  cabbage ;  chlorine  will  be  set  free  at  the  positive  pole,  and  discharge  the  bh  e 
color,  while  calcium  will  be  set  free  at  the  negative,  which  will  be  at  once  converted  into 
oxide  of  calcium  or  lime,  and  change  the  vegetable  blue  to  gre*>n. 

52.  Repeat  the  same  exper  ment  with  chloride  of  calcium,  colored  by  the  blue  solu- 
tion of  litmus  ;  the  color  will  be  removed  in  the  positive  tube,  but  no  change  produced 
upon  it  in  the  negative. 

53.  Repeat  the  same  experiment  with  chloride  of  calcium,  colored  blue  by  sulphate 
of  indigo:  the  color  will  be  discharged  in  the  positive- tube,  but  remain  unchanged  in 
the  negative. 

54.  Repeat  the  same  experiment  with  chloride  of  calcium,  colored  by  black  ink  ;  the 
black  will  be  discharged  in  the  positive  tube,  but  remain  unchanged  in  the  negative. 

55.  Pass  the  current  through  a  strong  solution  of  corrosive  sublimate  (chloride  of 
mercury  )  having  a  little  blue  tincture  of  cabbage  in  the  positive  tube ;  chlorine  will  be 
set  free  at  the  positive  pole,  discharging  the  blue  color,  and  mercury  at  the  negative 
pole,  which  should  be  made  of  gold  foil ;  this  will  be  at  once  whitened  by  the  deposit  of 
the  mercury  ;  a  small  gold  coin  will  answer  very  well  for  the  negative  pole. 

56.  Pass  the  current  through  a  solution  of  sulphate  of  topper;  sulphuric  acid  will 
fee  set  free  at  the  positive  pole,  and  copper  deposited  at  the  negative  pole;  eon.etimes 
the  oxide  of  copper  is  deposited  instead  of  the  pure  metal ;  but  if  the  solution  be  of 
moderate  strength,  the  hjdrcgen  which  is  set  free  at  the  same  pole  will  decompose  the 
oxide,  and  set  free  metallic   copper.      This  is  a  case  of  secondary  decomposition  (see 
§  371  )  and  illustrates  the  art  of  electrotyping. 

57.  To  decompose  potash,  pour  a  strong  solution  of  caustic  potash,  which  has  been 
carefully  protected  from  the  «ir.  upon  the  surface  of  mercury  in  a  small  iron  cup  ;  con- 
nect this  cup  with  the  negative  pole  of  the  battery,  then  apply  to  the  surface  of  the  solu- 
tion a  platinum  wire  connected  with  the  positive  pole ;  oxygen  gas  will  be  set  free  at  the 
positive  pole,  and  metallic  potassium  at  the  negative  pole,  which  will  immediately  form  an 
amalgam  with  the  mercury,  giving  it  a  puffy  appearance.     The  potassium  may  be  ex- 
tracted from  the  mercury,  and  obtained  in  a  pure  state,  by  distillation  in  an  atmosphere 
of  nitrogen. 

BB.  Place  a  piece  of  solid  caustic  potash,  slightly  moistened,  upon  a  flat  piece  of  gas- 
carbon,  hollowed  into  a  cup,  and  attached  to  the  negative  pole  of  the  battery  in  the  in- 
strument represented  in  Fig.  159,  or  in  Duboscq's  electric  lamp,  Fig.  160,  and  then 
bring  down  upon  it  a  piece  of  platinum  wire,  or  gas  carbon,  attached  to  the  positive  pole  : 
oxygen  will  be  set  free  upon  the  wire,  and  the  metal  potassium  in  the  carbon  cup, 
burning,  as  it  forme,  with  a  beautiful  red  flame. 

59  Another  mode  of  performing  the  same  experiment,  is  to  excavate  a  small  cavity 
in  a  piece  of  caustic  potash,  introduce  into  it  a  globule  of  mercury,  and  place  the 
potash  upon  a  plate  of  platinum ;  the  positive  pole  is  then  to  be  connected  with  the 
platinum  plate,  and  the  negative  with  the  mercury  ;  the  potarh  is  slowly  decomposed, 
oxvgen  ?et  free  at  the  positive  pole,  and  potassium  at  the  negative,  which,  as  frst  as 
formed  amalgamates  with  the  mercury  ;  it  may  be  obtained  in  a  pure  state  by  distilla- 
tion in  nitrogen,  as  described  in  experiment  57. 

60.  The  decomposition  of  soda,  and  the  formation  of  metallic  sodium,  may  be  accom- 


EXPERIMENTS    ON    GALVANISM.  535 

plished  by  subjecting  a  piece  of  caustte  soda,  slightly  moistened,  to  the  same  treatment ; 
oxygen  will  be  set  free  at  the  positive  pole,  and  metallic  sodium  at  the  negative  pole, 
which  may  be  obtained,  by  distillation,  from  the  mercury.  If  the  experiment  be  per- 
formed with  charcoal  poles,  the  sodium,  as  it  burns,  will  emit  a  yellowish  light,  and  may 
thus  be  distinguished  from  potassium. 

61.  If  some  of  the  potassium  or  sodium  amalgam,  obtained  in  these  experiments,  be 
thrown  into  water,  the  potassium  and  sodium  will  quit  the  mercury,  and  decompose  the 
•water,  on  account  of  their  strong  affinity  for  oxygen,  uniting  with  it  to  form  potash  and 
eoda,  and  setting  free  the  hydrogen,  which  will  at  once  take  lire  and  burn,  with  red  flame 
for  the  potassium,  and  yellow  for  the  sodium. 

62.  Kepeat  experiment  57,  substituting  for  the  solution  of  potash,  a  strong  solution 
of  chloro-hydrate  of  ammonia    (sal  ammoniac) ;   the  mercury  will  greatly  increase  in 
bulk,  and  an  amalgam  be  formed  with  the  so-called  metal  ammonium  at  the  negative  pole, 
while  oxygen  will  be  set  free  at  th«  positive  pole.     This  metal  ammonium  is  supposed  to 
be  a  compound  of  hydrogen  and  ammonia,  and  to   have  for   its  symbol,  N  H*.     This 
experiment  may  be  varied  by  placing  a  piece  of  solid  sal-ammoniac   upon  a  platinum 
plate,  and  a  globule  of  mercury  in  a  small  excavation  made  in  its  upper  surface,  witii 
which  the  negative  pole  should  be  connected ;  the  positive  pole  should  be  connected  with 
the  platinum  plate ;  the  ammonium  amalgam  will  be  formed  as  before. 

63.  Pass  the  current  through  4  cups  of  acidulated  water,  connected  by  platinum 
wires,  and  arranged  'as  in  Fig.  168,  and  observe  that  two  poles  are  formed  in  each  cup, 
one  of  which  discharges  oxygen,  and  the  other  hydrogen,  and  always  in  the  same  order; 
on  inverting  a  tube,  closed  at  one  end,  and  filled  with  water,  over  each  pole,  an  equal 
quantity  of  hydrogen  will  be  collected  in  all  the  hydrogen  tubes,  and  an  equal  quantity 
of  oxygen  in  all  the  oxygen  tubes. 

64.  Arrange  the  apparatus  as  in  the  preceding  experiment;  at  the  same  time  intro- 
duce a  voltameter  into  the  circuit,  (see  Fig.  170,)  having  two  tubes,  closed  at  the  top, 
inverted  in  it,  and  filled  with  water ;  the  same  amount  of  hydrogen  and  oxygen  will  be 
collected  in  these  tubes  as  in  those  placed  in  any  of  the  4  cups.     This  shows  the  equality 
of  the  circulating  force  in  every  part  of  the  circuit. 

65.  Arrange  the  4  cups  as  before,  except  that  instead  of  water,  in  the  1st  cup  let  a 
solution  of  iodide  of  potassium  be  placed,  mixed  with  starch  ;  in  the  2d,  a  strong  solution 
of  chloride  of  sodium — common  salt,  colored  blue  by  sulphate  of  indigo ;  in  the  3d,  a 
solution  of  nitrate  of  ammonia,  colored  blue  by  purple  cabbage  ;  in  the  4th,  a  solution 
of  sulphate  of  copper ;  let  the  poles  in  each  cup  be  separated  by  pieces  of  thick  paper ; 
connect  with  the  battery,  and  observe  the  formation  of  two  poles  in  each  cup,  as  before, 
and  that  the  iodine,  chlorine,  nitric  acid,  and  sulphuric  acid,  on  the  one  hand,  and  on 
the  other,  the  potassium,  sodium,  ammonia,  and  copper,  are  set  free  at  corresponding 
poles. 

66.  This  experiment  may  be  better  performed  with  U  tubes.    Take  5  U  tubes,  fix 
them  in  supports,  so  that  they  may  be  placed  in  a  line,  and  connect  them  by  slips  of  pla- 
tinum.    Into  the  1st,  pour  a  solution  of  iodide  of  potassium,  having  starch  mixed  wit  i 
it  in  the  left  hand  leg,  and  purple  cabbage  in  the  right ;  in  the  2d,  a  solution  of  chloride 
of  sodium,  colored  blue  in  both  legs  by  purple  cabbage  ;  in  the  3d,  a  solution  of  nitrate 
of  ammonia,  also  colored  blue  in  both  legs,  by  purple  cabbage  ;  in  the  4th,  a  solution  of 
sulphate  of  copper,  colored  blue  in  the  left  hand  leg  only,  with  purple  cabbage  ;  and  in 
the  5th,  acidulated  water.     Then  connect  the  starch  end  of  U  tube  1  with  the  positive  pole 
of  the  battery,  and  U  tube  5  with  the  negative ;  observe  that  the  iodine,  chlorine,  nitric 
acid,  sulphuric  acid,  and  oxygen,  on  the  one  hand,  and  the  potassium,  sodium,  ammonia, 
copper,  and  hydrogen,  on  the  other,  are  discharged  at  corresponding  poles,  showing  the 
similarity  of  their  electrical  relations;  the  iodine  may  be  known  by  the  blue  it  imparts 
to  starch;  the  chlorine  by  its  bleaching  ;  nitric  acid,  and  sulphuric  acid,  by  reddenirg 
purple  cabbage ;  the  oxygen  by  its  effect  on  a  taper ;  the  potassium,  sodium,  and  amn  o- 
nia,  by  turning  the  purple  cabbage  green;  the  copper  by  its  metallic  lustre;  the  hydro- 
gen by  its  quantity  and  inflammability. 

67.  Arrange  three   cups  in  the  manner  described  in  §  372,  filling  the  three  cups  with 
solution  of  sulphate  of  soda,  tinged  blue  by  tincture  of  cabbage,  and  connecting  them  bv 
shreds  of  asbestus,  or  syphons  of  glass  tube  filled  with  the  same  solution  ;  on  passing  the 
current,  the  soda  will  collect  in  the  negative  cup,  turning  it  green,  and  the  acid  in  the 
positive  cup  turning  it  red,  without  producing  the  slightest  change  in  the  color  of  the 
intermediate  cup,  though  both  have  passed  through  it. 

68.  Repeat  this  experiment,  filling  the   cup  A,  on  the  left,  with  sulphate  of  soda, 
tinged  blue  ;  the  cup  c,  on  the  right,  with  pure  water,  also  tinged  blue ;  and  the  middle 
cup  B,  with  strong  potash  ;  on  passing  the  current,  the  acid  will  collect  in  the  right  hand 
cup,  turning  the  blue  to  red.  and  in  so  doing,  pass  directly  through  the  potash  in  the  cup, 
B,  without  any  hindrance,  though  the  affinity  between  them  is  intense ;  the  soda  will  collect 
in  the  cup  A,  and  turn  it  green,  as  before.     If  the  sulphate  of  soda  be  placed  in  the  right 
hand  cup,  the  middle  cup  be  filled  with  strong  sulphuric  ac'd,  and  the  left  hand  cup 
with  pure  water,  tinged  blue,  the  soda  will  pass  straight  through  the  acid  without  affect- 


61 6  ELECTHOTYPINGr  AND    ELECTRO-MAGNETISM. 

Ing  it,  notwithstanding  the  strong  affinity  between  them,  into  the  cup  A,  audits  pres- 
ence there  may  be  detected  by  its  turning  the  vegetable  blue  to  green. 

69.  Arrange  the  three  cups  as  before,  and  into  the  middle  eup  introduce  a  strong  so- 
lution of  caustic  baryta,  or  strontia ;  in  the  left  hand  cup,  sulphate  of  soda  tinged  blue ; 
in  the  right  hand  cup,  pure  water  colored  blue ;  on  passing  the  current,  the  sulphate  of 
soda  will  be  decomposed,  the  soda  will  collect  in  the  left  hand  cup,  turning  it  green,  but 
the  acid,  in  passing  through  the  middle  cup,  will  be  caught  by  the  baryta,  and  precipi- 
tated to  the  bottom,  in  the  form  of  sulphate  of  baryta,  while  no  effect  at  all  will  be  pro- 
duced upon  the  right  hand  cup.    In  like  manner,  if  a  solution  of  nitrate  of  baryta  be 
placed  in  the  right  hand  cup,  strong  sulphuric  acid  in  the  middle,  and  pure  water  col- 
ored blue,  in  the  left  hand  cup,  the  nitrate  of  baryta  will  be  decomposed,  the  nitric  acid 
will  remain  in  the  right  hand  cup,  but  the  baryta,  on  its  way  to  the  left  hand  cup,  will 
be  caught  by  the  sulphuric  acid,  and  precipitated  to  the  bottom,  in  the  form  of  sulphate 
of  baryta :  the  left  hand  cup  will  remain  unchanged.    1'or  an  explanation  of  this,  see 
§  374. 

70.  Electrotyping,  Plating,  and  Gilding'.    Place  a  small  silver  coin,  having 
a  platinum  wire  attached  to  it,  in  a  solution  of  sulphate  of  copper,  and  into  the  ttn  e 
solution  introduce  a  small  piece  of  zinc ;  no  change  will  be  produced  in  either  metal  so 
long  as  both  are  kept  apart,  but  as  soon  as  a  connection  is  formed  between  them  by  means 
of  the  wire,  copper  will  be  deposited  upon  the  silver ;  this  shows  the  tendency  of  the  me- 
tals to  be  deposited  upon  the  conducting  plate  of  the  battery,  which  is  always  negative 
within  the  liquid,  and  positive  without,  Fig.  139,  140,  166. 

71.  Let  two  slips  of  platinum  be  connected  with  the  poles  of  the  battery,  and  intro- 
duced into  a  solution  of  sulphate  of  copper,  the  negative  pole  will  at  once  be  coated  with 
copper,  while  oxygen  will  be  discharged  upon  the  positive.    Repeat  the  same  experiment 
•with  nitrate  of  silver ;  metallic  silver  will  be  deposited  upon  the  negative  pole.    If  acetate 
of  lead  be  employed,  a  deposit  of  metallic  lead  will  be  obtained ;  and  so  with  other  metal- 
lic solutions. 

72.  To  copy  a  coin,  take  an  impression  from  it  in  beeswax  ;  then  blow  over  its  surface 
some  fine  plumbago,  in  order  to  give  it  a  conducting  surface ;  then  attach  it  by  a  wire  to 
the  negative  pole  of  the  battery,  taking  care  that  the  wire  actually  touches  the  plumbago, 
and  introduce  it  into  a  sulphate  of  copper  solution  ;  then  bring  the  positive  pole  of  the 
battery,  which  may  be  a  slip  of  clean  copper,  into  the  same  solution,  and  the  wax  mould 
will  at  once  receive  a  deposit  of  copper,  which  will  steadily  increase  in  thickness ;  it  may 
easily  be  separated  from  the  wax  and  an  exact  reproduction  of  the  coin  obtained.     The 
solution  for  depositing  copper  is  best  prepared  by  making  a  saturated  solution  of  sulphate 
of  copper,  and  then  diluting  it  to  one-half,  or  one-third,  of  its  bulk,  with  a  mixture  of 
one  measure  of  sulphuric  acid  with  eight  of  water. 

73.  If  the  article  to  be  copied  be  made  of  plaster,  it  should  be  dipped  in  melted  stea- 
rine,  and  then  coated  witb  plumbago,  as  above  described,  before  being  placed  in  the  bath  ; 
or,  if  it  be  a  medallion,  it  may  be  wetted  by  holding  it  in  water,  with  the  face  upward, 
until  the  liquid  has  thoroughly  penetrated  it ;  then  tie  a  slip  of  paper  around  the  rim, 
and  pour  melted  white  wax  into  the  cup  thus  formed  ;  the  wax  impression  is  then  to  be 
coated  with  plumbago,  as  above  described ;  gutta-percha  may  also  be  used  to  take  im- 
pressions. 

74.  In  order  to  plate  with  silver,  the  articles  must  be  well  cleaned,  and  attached  to 
the  negative  pole,  in  a  solution  consisting  of  two  parts  of  cyanide  of  potassium,  dissolved 
in  250  parts  of  water ;  to  the  positive  pole,  a  silver  plate  must  be  attached,  in  order  to 
keep  up  the  strer.gth  of  the  solution. 

75.  For  gilding,  articles  must  be  very  carefully  cleansed  and  attached  to  the  negative 
pole,  in  a  bath  consisting  of  one  grain  of  chloride  of  gold,  and  ten  grains  of  cyanide  of  po- 
tassium, dissolved  in  200  grains  of  water ;  a  piece  of  gold  must  be  suspended  from  the  pos- 
itive pole,  in  order  to  keep  up  the  strength  of  the  solution.     In  performing  these  experi- 
ments upon  the  deposition  of  metals,  many  points  of  detail  connected  with  the  strength 
of  the  solution,  the  power  of  the  battery,  and  the  degree  of  temperature  can  only  be 
learned  by  practice.     See  Davis'  Manual  of  Magnetism. 

76.  Magnetism,   and   Electro-Magnetism.     The  attractive  power  of  the 
magnet  may  be  shown  by   applying  either  extremity  of  a  magnet  to  a  mass  of  iron 
filings,  or  to  any  collection  of  small  bits  of  iron  ;  the  filings  and  iron  pieces  will  attach 
themselves  strongly  to  each  end  of  the  bar. 

77.  That  a.  magnet  possesses  two  poles  of  opposite  properties,  may  be  shown  by  sus- 
pending a  delicate  magnetic  needle  by  a  thread,  ns  in  Fig.  174,  and  observing  that  its 
north  pole  is  repelled  and  its  south  pole  attracted  by  the  north  pole  of  a  second  mag- 
netic needle  held  near  each  pole  successively. 

78.  The  repulsive  power  of  the  same  poles,  and  the  attractive  power  of  the  opposite 
poles  of  two  different  magnetic  needles  may  be  shown,  by  trying  the  effect  of  each  mag- 
netic pole  of  a  bar  magnet  successively  upon  the  poles  of  a  delicate  magnetic  needle,  sus- 
pended by  a  fine  thread.  Fig.  174. 

79.  The  directive  action  of  the  earth  upon  a  magnet  may  be  shown  by  mounting  a 


EXPERIMENTS    ON    GALVANISM. 


537 


.  magnetic  needle  upon  a  pivot,  as  in  Fig.  175,  and  observing  that  it  immediately  takes  a 
north  and  sonth  position,  and  that  the  magnetic  poles  very  nearly  coincide  with  t~e  ex- 
tremities  of  its  axis. 

80.  The  effect  of  neutralizing  the  directive  action  of  the  earth  upon  a  magnetic  nee- 
dle may  be  shown  by  fastening  a  second  needle,  with  poles  reversed,  directly  beneath  the 
first,  as  in  the  astatic  needle,  Fig.  176,  and  observing  that  the  earth  no  longer  compels 
the  needle  to  assume  a  north  and  south  position. 

81.  The  non-directive  tendency  of  the  astatic  needle  may  be  shown  by  observing  that, 
•when  moved  from  the  magnetic  meridian,  it  does  not  tend  to  return  to  it  again.     That  it 
has  not  lost  its  magnetic  power,  may  be  proved  by  the  action  of  a  bar  magnet,  when 
brought  near  it. 

84.  The  induction  of  magnetism  in  a  piece  of  soft  iron  may  be  shown  by  taking  up 
a  common  nail  by  the  end  of  a  bar  magnet,  and  observing  that  the  extremity  of  the  nail 
is  itself  possessed  of  attractive  power,  has  become  magnetic,  and  will  attract  a  second 
small  piece  of  iron,  when  applied  to  it.  and  this  another,  and  so  on  in  succession  so  long 
as  the  connection  with  the  original  magnet  is  maintained,  Fig.  177. 

8  *.  To  show  the  dia-magnetic  effect  of  the  magnet  upon  certain  substances,  suspend 
a  delicate  needle  of  bismuth  or  antimony  by  a  thread  between  the  poles  of  a  powerful 
horse  shoe  magnet,  and  it  will  at  once  assume  an  equatorial  position,  Fig.  1(9.  Try 
the  same  experiment  with  a  stick  of  Phosphorus. 

84,  The  same  dia  magnetic  power  may  also  be  shown  by  suspending  a  small  cube  of 
copper  between  the  poies  of  a  powerful  electro-magnet  by  a  thread  of  twisted  silk, 
which  causes  it  to  turn  round  with  great  rapidity  ;  the  instant,  however,  that  the  elec- 
trical current  circulates,  and  the  electro-magnet  becomes  excited,  the  motion  of  the  cube 
is  completely  arrested ;  this  is  not  owing  to  any  attractive  action  exerted  by  the  poles, 
for  it  is  well  known  that  no  such  attraction  is  exerted  upon  copper,  but  to  a  powerful 
dia-magnetic  action,  which  acts  at  right  angles  to  the  magnetic  axis. 

8  5.  The  dia-magaetism  of  liquids  may  be  shown  by  enclosing  different  solutions  in 
small  tubes  of  very  thin  glass  ;  if  the  liquids  are  magnetic,  like  the  solutions  of  iron, 
nickel,  and  cobalt,  the  tubes  take  up  their  position  in  the  magnetic  axis  ;  if  dia-magnetic, 
like  water,  alcohol,  ether,  spirits  of  turpentine,  &c.,  they  occupy  the  equatorial  axis. 

88.  The  dia-magnetism  of  gases  may  be  shown  by  the  apparatus  indicated  in  Fig. 
183 ;  also,  by  placing  a  lighted  candle  between   the  poles  of  the  electro-magnet.  Fig. 
255,  the  pillar  of  gas  rising  from  the  wick   will  cease  to  ascend,  and  be  turned  off  at 
right  angles  upon  a  line  corresponding  with  the  magnetic  equator. 

87.  To  show  that  the  wire  carrying  the  bitter/  current  itself  becomes  magnetic,  con- 
nect the  poles  of  a  series  of  several  p  lirs  of  Grove's  battery,  by  means  of  a  short  copper 
wire,  and  apply  iron  filings ;  they  will  adhere  equally  all  around  the  circumference  of 
the  wire,  forming  circular  bands  ;  when  the  circuit  is  broken  the  iron  filings  will  fall  off; 
but  if  steel  filing*  be  employed,  a  part  of  them  will  remain  attached. 

83.  To  show  the  effect  of  the  gilvanic  current  upon  the  magnet,  arrange  the  wire 
connecting  the  pole^  of  a  battery,  and  carrying  the  current,  on  a  line  running  north 
and  south,  the  direction  of  the  current  being  from  the  south  to  north,  and  place  a 
delicate  magnetic  needle,  supported  upon  a  fine  point,  directly  beneath  ir,,  as  in  Fig. 
172 ;  the  north  pole  will  move  to  the  west,  and  the  south  to  the  east ;  place  the  nee  lie 
above  the  wire,  and  on  either  side,  and  observe  the  effect;  finally,  reverse  the  current, 
and  observe  the  reversion  of  all  the  movements. 

89.  The  effect  of  the  wire  carrving  the  current,  upon  the  magnetic  needle,  maybe  best 
seea  by  making  use  of  a  magnetic  needle   half  brass.     In  this  instrument,  the  steel  nee- 
dle is  wholly  upon  one  side  of  the  poiot  of  support,  and  is  counterpoised  by  a  brass 
weight  on  the  other  side.     By  this  arrangement,  the  action  of  the  electrical  current  upon 
the  pole  which  points  to  the  pivot  (let  it  be  the  south  pole  )  can  have  no  influence  in 
turning  the  mignet,  and  its  motion  will  be  determined  solely  by  the  action  of  the  cur- 
rent upon  the  north  pole.     The  effect  of  this  arrangement  will  be,  to  make  the  tendency 
of  the  magaet  to  rotate  around  the  pole  more  apparent,  but  no  actual  rotation  can  be 
obtained. 

90.  That  the  gvlvanic  current  induces  magnetism,  may  be  shown  by  winding  a  picre 
of  soft  copper  wire  spirally  around  a  glass  tube,  in  a  right  hand  direction,  and  connecting' 
the  two  extremities  of  the  coil  with  the  poles  of  the  battery ;  then  introduce  into  the ' 
tube  a  rod  of  soft  iron,  and  bring  a  magnetic  needle  near  either  end  :  it  will  be  found 
that  the  iron  rod  has  become  strongly  magnetic,  the  rorth  pole  being  at  the  extremity  at 
which  the  current  leives  the  coil;  apply  iron  filings,  or  any  small  pieces  of  iron,  to  fie 
rod,  and  they  will  be  found  to  be  strongly  attracted  ;  break  the  connection,  and  the  mng- 
nerism  will  be  destroyed,  and  the  .'irticles  will  fall ;  re  establish  the  connection,  and  the 
magnetism  will  be  restored  ;  Fig.  182. 

91.  Reverse  the  current,  and  the  position  of  the  pole''  will  be  reversed. 

9*?.  Wind  a  wire  around  a  second  similar  tube,  in  the  left  hand  direction,  and  the 
position  of  the  poles  will  be  reversed,  the  nortii  pole  being  at  the  extremity  at  which  the 
current  enters  the  wire  ;  Fig.  183. 


YOLT A— ELECTRIC    INDUCTION. 

9"*.  Connect  a  mounted  helix,  Fig.  184,  with  the  battery:  the  helix  itself  becomes 
magnetic,  before  the  introduction  of  the  iron  rod.  as  shown  by  its  effect  on  the  magnetic 
needle,  and  upon  iron  filings  ;  then  introduce  the  iron  rod,  and  observe  that  the  poles  of 
the  rod  are  the  reverse  of  those  of  the  helix,  the  rod  being  magnetized  by  indue  ion. 

94.  To  show  the  de.icacy  of  the  current,  measured  by  the  common  galvanometer.  Fig. 
185,  provide  a  piece  of  zinc,  and  another  of  copper,  one  inch  square,  and  immerse  them 
in  a  small  quantity  of  acidulated  water,  taking  care  that  they  do  not  touch  each  other, 
then  transmit  the  current  through  the  galvanometer. 

95.  To  show  the  extreme  delicacy  of  the  a&tatic  galvanometer,  immerse  a  piece  of  zinc, 
and  another  of  copper,  about  |th  of  an  inch  square,  in  acidulated  water,  and  connect 
•with  the  astatic  galvanometer  ;  Figs.  188  and  187. 

9S.  To  show  tne  magnetic  influence  of  the  liquid  part  of  the  circuit,  suspend  a  mag- 
netic needle,  as  in  Fig.  188. 

97.  To  show  the  truth  of  Ampere's  theory,  mount  a  helix  of  wire,  as  in  Fig.  190,  and 
observe  that  one  extremity  is  affected  with  north  polarity,  and  the  other  with  south,  as 
shown  by  the  magnetic  needle,  when  brought  near  it. 

93.  Arrange  two  helices,  as  in  Fig.  191,  and  observe  that  they  act  exactly  as  two  mag- 
nets would,  under  similar  circumstances. 

99.  To  show  that  the  wire  carrying  the  current,  and  the  magnetic  needle,  tend  to  re- 
volve around  each  other,  and  that  their  action  is  mutual,  try  the  experiment  with  De  la 
Rive's  ring,  Fig.  192,  first  with  one  pole  of  the  magnet,  then  with  the  other. 

)  00.  To  show  the  confirmation  of  Ampere's  theory,  provide  a  ring,  mounted  as  in  Fig. 
193,  through  which  the  current  is  passing,  and  observe  that  it  arranges  itself  at  right 
angles  to  the  magnetic  meridian. 

1  Ol.  Transmit  the  current  through  the  magic  circle,  Fig.  197,  and  observe  the  heavy 
weights  which  it  will  support. 

1 021.  Suspend  a  heavy  weight  from  a  powerful  electro-magnet,  and  observe  the  effect  of 
breaking  and  forming  the  battery  connection  ;  Fig.  196. 

1O3.  To  illustrate  the  principle  of  the  telegraph,  send  the  galvanic  current  through  a 
wire,  around  a  room,  by  connecting  one  extremity  with  the  positive,  and  the  other  witli 
the  negative  j>oJe  of  a  battery,  and  cause  it  to  circulate  through  an  electro-magnet, 
having  a  movable  armature  suspended  over  it,  at  the  other  end  of  the  apartment,  and  ob- 
serve the  effect  upon  this  electro  magnet  of  breaking  and  establishing  the  battery  con- 
nection ;  or  use  Aiorse's  indicator,  Fig.  199. 

1O*.  To  show  the  application  of  electro-magnetism  to  the  production  of  motion, 
make  use  of  the  instrument  represented  in  Fig.  208:  also  any  of  the  electro-magnetic 
engines  sold  by  the  philosophical  instrument-makers. 

1O5.  Volta-Electric  Induction.  The  induction  of  a  secondary  current  of  elec- 
tricity, by  a  primary  current,  may  be  shown  by  the  apparatus  represented  in  Fig.  214. 
A  delicate  galvanometer  must  be  attached  by  wires  to  the  extremities  of  the  outer,  or  the 
secondary  coil ;  then,  on  forming  the  connection  between  the  piimary  coil  and  the  bat- 
tery, the  needle  of  the  galvanometer  will  be  deflected  in  such  a  way  as  to  indira'e  the 
passage  of  a  secondary  current  in  a  reverse  direction  to  that  of  the  primary  current ; 
the  instant  the  connection  with  the  batfc-ry  is  broken,  the  needle  will  be  deflected  in  the 
opposite  direction,  indicating  the  induction  of  a  current  in  the  same  direction  as  the 
primary  current. 

10S.  That  this  effect  takes  place  through  a  considerable  distance  may  be  shown  by 
the  apparatus  represented  in  Fig.  215. 

1 0  7.  That  a  secondary  current  is  induced  by  the  approach  and  removal  of  Ihe  pri- 
mary current  may  be  shown  by  the  apparatus  represented  in  Fig.  216. 

103.  The  induction  of  a  secondary  current,  in  the  primary  wire  itself,  or  the  extra- 
current,  may  be  shown  by  the  apparatus  represented  in  Fig.  217. 

109.  The  character  of  the  induced  extra-current  may  be  shown  by  the  apparatus  in- 
dicated in  Figs.  215,  226 ;  vivid  sparks  are  produced  by  drawing  the  wire  of  the  battery 
over  the  piece  of  ribbed  iron,  and  violent  shocks  are  given. 

110.  The  tertiary  and  quaternary  currents  may  be  shown  by  Henry's  coils.  Fig  218. 

111.  Miene*.o-T31lectrictty.     That  a  secondary  electrical  current  is  induced  by 
magnetism,  may  be  shown  by  the  apparatus  represented  in  Fig.  219      On  introducing 
the  permanent 'magnet  into  the  interior  of  the  coil,  the  needle  of  the  galvanometer  is 
deflected  powerfully,  showing  the  induction  of  an  electrical  current  in  the  ii-verse  direc- 
tion from  the  currents  flowing  around  the  magnet,  according  to   the  theory  of  M.  Am- 
pere.   On  reversing  the  magnet,  the  needle  is  deflected  in  the  opposite  direction. 

112.  Remove    the    magnet  altogether,  and  introduce   in   its   place  a  b«r  of  soft 
Iron:  this  will  become  magnetized  by  induction  as  soon  as  a  magnet  is  brought  r.eur  its 
free  extremity  ;  at  the  instant  this  takes  place,  the  needle  of  the  grxlvanorretor  will  be 
ieflectcd  as  before ;  when  the  magnet  is  removed,  the  iron  bar  will  lose  its  magnetism 
tod  be  deflected  in  the  opposite  direction. 

:    113.  The  same  effects  may  also  be  shown  by  the  apparatus  represented  in  Fie.  1^4. 
1. 14.  The  production  of  sparks  by  the  current  thus  induced,  may  be  shown  by  the  ap» 


EXPERIMENTS    OX    GALVANISM.  539 

paratus  represented  in  Fig.  220.  On  touching  the  mounted  permanent  magnet  A  B, 
with  the  rod  of  soft  iron,  N  s,  wound  with  a  coil  of  copper  wire,  tae  two  ends  of  whica 
nearly  meet,  the  iron  rod  will  be  magnetized  by  induction,  and  at  the  same  instant 
a  bright  spark  Hash  between  the  wires. 

Ho.  If  an  electro-magnet,  while  actuated  by  the  battery  current,  be  brought  near  a 
coil  of  wire  connected  witn  a  delicate  galvanometer,  a  secondary  current  of  electricity 
will  be  induced. 

116.  That  an  electrc-magnet,  magnetized  and  de-magnetized,  will  induce  an  electrical 
current  in  a  closed  wire  may  be  conclusively  shown  by  attaching  a  battery  to  one  pair  of 
the  wires  of  Faraday's  ring;  Fig.  223. 

117.  The  same  fact  may  also  be  shown  by  introducing  a  bar  of  soft  iron  into  the  cen- 
tre of  the  primary  coil  represented  in  Fig.  214,  on  completing  and  breaking  connection 
with  the  battery  the  iron  bar  is  magnetized,  and  de-magnetized,  and  a  muca  more  de- 
cided effect  exerted  upon  the  galvanometer  than  when  the  coils  are  used  alone.     This  is 
a  case  of  Volta-Magneto-electric  Induction. 

113.  The  same  fact  may  be  shown  by  the  apparatus  represented  in  Fig  2?2,  and  also 
that  the  strength  of  the  induced  current  of  electricity  as  shown  by  the  galvanometer  is 
proportioned  to  the  number  of  soft  iron  wires  introduced,  or  in  other  words  to  the  size 
and  power  of  the  electro-magnet. 

119.  Arago's  rotations  may  be  shown  by  the  apparatus  represented  in  Fig.  224. 

120.  Pace's  Separable  Halicas.     The  properties  of  the  induced  secondary 
currents  may  be  exhibited  by  Page's  separable  helices,  Fig.  226      If  the  handles  con- 
nected with  the  extremities  of  the  secondary  coil  be  tightly  grasped,  shocks  will  be  expe- 
rienced, when  the  connection  with  the  battery  is  rapidly  completed  and  broken,  either  by 
drawing  one  polar  wire  over  the  rasp,  or  by  the  break-piece,  even  when  there  are  no  wires 
in  the  interior  of  the  inner  coil;  introduce  the  wires  one  by  one,  and  taesnocks  \vi,l 
gradually  increase  in  intensity  till  they  become  intolerable,  and  the  hands  become  so 
tightly  fastened  to  the  handles  that  it  will  be  impossible  to  open  them,  and  the  sciutia.i- 
tions  upon  the  rasp  and  break-piece  will  become  very  brilliant. 

121.  Instead  of  the  bundle  of  wires  substitute  a  rod  of  soft  iron,  the  shocks  and 
sparks  will  be  considerably  diminished. 

122.  If  the  bundle  of  wires  or  the  iron  rod  be  introduced  gradually,  the  spark  and 
shock  increase  as  it  enters;  in  this  manner  the  intensity  of  the  shock  may  be  regulated. 

123.  Pass  a  glass  tube  over  the  iron  wires  in  the  helix,  and  the  eifect  will  remain  un- 
diminished,  but  if  a  brass  tube  be  employed,  the  shocks  and  sparks  will  cease  alto- 
gether 

124.  If  the  battery  wire  be  moved  slowly  over  the  rasp,  distinct,  powerful  single 
shocks  are  obtained  ;  if  moved  more  rapidly,  the  arms  are  convulsed  violently. 

125.  The  strength  of  the  shock  depends  much  upon  the  extent  of  contact  surface 
between  the  hands  and  the  metallic  conductors ;  the  shocks  will  be  much  lessened  if 
two  wires  be  used  instead  of  handles,  and  still  more  if  t  ic  wires  are  held  lightly  in  tae 
fingers.     The  shocks  are  greatly  increased  if  the  hands  are  moistened  with  salt  water. 

125.  If  the  handle  connected  with  the  positive  cup  of  the  secondary  helix  be  held  ii 
the  right  hand,  and  the  one  connected  with  the  negative  cup  in  the  left  hand,  the  left 
hand  and  arm  will  experience  the  most  powerful  shocks,  and  be  the  most  violently  con- 
vulse 1.  In  determining  the  positive  cup,  the  terminal  secondary  produced  by  breaking 
contact,  should  be  alone  taken  into  account ;  the  initial  secondary  may  be  disregarded 

127.  If  the  ends  of  the  secondary  wire  be  put  into  water,-a  peculiar  shock  mav  be 
taken  by  putting  the  fingers  or  h  inds  into   the  w.iter,  so  as    to  make  the  current  p  is* 
through  them.     Th^  current  prefers  a  piss  ige  through  the  body  to  that  through  the 
water,  between  the  fingers  ;  if  the  conducting  power  of  the  water  be  made  superior  to 
that  of  the  human  body  by  the  addition  of  a  small  quantity  of  common  salt,  little  or  no 
shock  will  be  perceived. 

128.  If  a  delicate  galvanometer  be  connected  with  the  extremities  of  the  secondary 
coil,  the  needle  will   be  deflected  in  opposite  directions,  and  equally  far,  whenever  the 
battery  circuit  is  completed  or  broken. 

129.  When  the  circuit  is  broken,  over  the  surface  of  mercury  by  Page's  circuit 
breaker,  §  452,  an  intensely  brilliant  spark  is  seen  in  both  cups,  if  the  quantity  of  mer- 
cury is  properly  regulated,  and  the  mercury  is  deflagrated  in  white  vapor. 

130.  If  water  or  oil  be  poured  upon  the  surface  of  the  mercury  the  sparks  will  be- 
come less  intense,  but  the  shocks  more  severe. 

131.  If  prepared  charcoal  points  (Expt.  25,)  are  attached  to  the  ends  of  the  secon- 
dary wires,  and  held  almost  in  contact,  a  beautiful  light  will  be  produced. 

132.  If  the  ends  of  the  secondary  coil  be  connected  with   two  fine  platinum  wires 
which  have  been  inserted  into  glass  tubes,  that  have  been  melted  on  the  wires  so  as  to 
cover  the  ends  completely,  and  then  filed  away  so  as  to  expose  the  tips  of  the  wires  and 
then  these  are  immersed  in  acidulated  water,  (Expt.  34,)  not  very  for  apart,  the  water 
vill  be  decompose  1,  and  Oxygen  and  Hydrogen  set  free,  both  on  completing  and  break- 
ing the  circuit.    As  the  platinum  wires  are  alternately  positive  and  negative,  each  ga« 


540    PAGE'S  SEPARABLE  HELICES,  RUHMKORFF'S  COIL. 

will  be  given  off  alternately  by  both  wires.  The  platinum  wires  may  be  coated  with  seal- 
ing  wax  instead  of  glass.  The  purpose  of  covering  them  is  to  confine  the  passage  of  the 
electrical  current  to  one  small  and  direct  path  from  tip  to  tip,  instead  of  allowing  it  to 
pass  between  tne  wires  along  the  whole  length  of  the  portions  immersed  in  tae  water. 

13^.  In  performing  tne  above  experiment,  rapid  discharges  are  heard  in  the  water, 
with  sharp  tickiug  sounds  audii  le  at  tne  distance  of  one  hundred  feet,  and  the  extiemi- 
ties  of  tne  wires  appear  in  the  dark,  one  constantly,  and  the  other  in  term  ittingly,  lumin- 
ous :  this  ticking  noise  and  the  sparks  are  produced  only  by  the  terminal  current  on 
breakiug  connection  with  the  battery. 

13*.  A  Leyden  jar  whose  iu.-ide  coating  is  connected  with  the  knob  by  a  continuous 
wire  may  be  slightly  charged,  and  feeble  sparks  be  obtained  from  it,  by  grasping  the 
jar  with  one  hand,  and  bringing  its  knob  into  contact  with  one  of  the  cups  of  the  sec- 
ondary helix,  and  then  establishing  a  connection  between  the  other  cup  of  the  heiix 
and.  the  outside  coating  of  the  jar,  by  means  of  a  wire  well  insulated  from  the  hiind. 

13d.  A  gold-leaf  electroscope,  Fig  115,  will  exhibit  a  considerable  divergence  of  its 
leaves,  if  its  cap  be  touched  by  a  wire  connected  with  either  cup  of  the  helix,  provided 
the  contact  be  made  at  the  moment  of  breaking  the  battery  circuit. 

13o.  If  the  instrument  be  arranged  horizontally,  and  a  bar  of  soft  iron  enclosed  in  a 
brass  tube  be  introduced  ioto  the  helix,  and  a  small  key  be  applied  to  one  end  of  the 
bar,  although  the  magnetism  of  the  bar  is  intermitted  with  every  break  in  the  battery 
circuit,  yet  being  almost  immediately  renewed,  the  key  will  not  fall.  This  experiment 
conclusively  proves  that  a  sensible  time  is  required  for  a  bar  to  lose  its  magnetic  power. 

137.  Ruhmkorii  s  Coil.     To  display   the  action   of  this  instrument  advanta- 
geously, from  four  to  eight  cells  of  Grove's  battery  are  generally  quite  sufficient.     The 
wires  leading  from  the  battery  are  to  be  attached  to  the  binding  i-crews  connected  with 
the  primary  coil,  and  great  care  must  be  taken  to  avoid  accidental  shocks,  by  breaking 
counection  with  the  battery,  by  means  of  the  commutator,  until  the  adjustment  of  the  ar- 
rangements for  the  proposed  experiment  is  complete.     For  the  successful  exhibition  of 
the  capabilities  of  the  coil,  the  experiments  must  be   performed  in  a  darkened  room. 
Care  must  be  takeu  that  the  condenser  is  attached  underneath  the  instrument,  as  de- 
scribed in  §  453,  pp  442,  443. 

138.  The  great  power  of  the  secondary  current  induced,  can  be  shown  by  connecting 
two  delicate  steel  needles  with  the  binding  screws  of  the  secondary  coil,  and  bringing 
them  within  a  few  inches  of  each  other ;  on  establishing  the  connection  with  the  batte- 
ry, a  secondary  current  of  great  intensity  will  Hash  through  the  wires  with  vivid  sparks  ; 
the  distance  may  be  incieased,  under  favorable  circumstances,  to  twenty  inches,  or  even 
more. 

1 39.  The  wire  from  which  the  current  passes  remains    old  enough  to  be  held  in  the 
fingers,  Fig  232;  the  other,  the  negative  wire,  becomes  ?o  hot  that  it  melts  into  a  giO- 
bule  of  liquid  iron,  and  if  paper  is  held  between  the  -.vires,  it  rapidly  takes  fire 

140.  If  a  reflection  of  these  points  be  thrown  upon  a  screen  by  means  of  Pubosrq's 
electric  lamp.  Fig.  160,  a  cone  of  vapor  will  appear  to  issue  from  the  point  if  each  wire, 
but  that  from  the  negative  wire  being  the  mo.-t  powerful,  seems  to  beat  back  the  stream 
from  the  positive  wire 

141.  In  place  of  the  steel  wires,  substitute  wires  of  copper,  of  zinc,  of  soft  iron,  of 
brass,  &c.;  in  all  ca^es  combustion  will  take  klace  with  the  j  loduction  of  the  charac- 
teristic liirht  of  the  metal. 

142.  O'i  directing  the  discharge  through  balls  of  the  different  metals,  Fig.  240,  the 
ppectrum  lines  peculiar  to  each  metal  may  be  seen  to  great  advantage  by  means  of  the 
spectroscope. 

14^.  On  passing  the  discharge  through  an  exhausted  Electric  Eg-,  Fg.  284,  a  beau- 
tiful luminous  trail  will  flash  from  one  ball  to  the  other.  Exhaust  the  receiver  more  per- 
fectly and  the  luminous  port  on  will  be  traversed  by  a  series  of  dark  bands  comentrio 
with  the  positive  ball.  Fig  234,  No.  2;  the  presence  of  a  little  vapor  of  phosphorus 
renders  these  bands  much  more  distinct.  Apply  the  finger  at  the  side  of  the  Egtr.  at 
the  same  time  cutting  off  the  connection  of  the  lower  knob  with  tV.e  negative  pole  of  the 
coil,  and  the  trail  will  suffer  a  curious  deviation  towards  the  finger.  Fig-  234,  No  3 

144.  Instead  of  the  Electric  Egg.  place  a  tumbler  r-f  Uranium  glass,  Fig.  235,  lined 
with  tin  foil,  upon  the  plate  of  an  air  pump  beneath  a  receiver,  and  brintr  down  a  sliding 
rol  until  it  touches  the  metallic  lining,  then,  on  establishing  a  connection  with  the  coil, 
a  beautiful  cascade  of  light  will  pour  over  the  edge  of  the  tumbler. 

145.  Pass  the  discharge  from  the  coil  through  Geissler's  tubes,  filled  with  different 
gates  which  have  been  more  or  loss  exhausted,  Figs.  236,  237,  and  observe  the  curious 
stratification  which  ensufg. 

1 4S.  Submit  the  light  of  Geissler's  tubes  to  observation  by  the  spectroscope,  Fig . 
240,  and  observe  the  beautiful  spectra  of  the  gases  which  are  thus  brought  out. 

147.  A  Levden  jar  may  be  charged  by  connecting  the  outer  coating.  Fig.  230,  wi'h 
one  of  the  poles  of  the  coil,  and  'he  inner  with  one  of  the  arms  of  a  discharger,  the 
.ether  arm  of  which  is  in  communkatioo.  with  the  opposite  pole  of  the  coil,  the  extremi- 


EXPERIMENTS    ON    GALVANISM.  -.  541 

.ties  being  two  or  three  inches  apart ;  allow  a  few  sparks  from  the  coil  to  pass,  and  then 
remove  and  discharge  the  jar  in  the  usual  manner. 

.  143.  Attach  one  of  the  secondary  wires  to  the  ball,  or  rod,  of  a  self-discharging  Ley  den 
jar,  and  tie  other  to  the  outside  surface,  so  arranged  that  the  discharger  may  be  brought 
within  half  an  inch  of  the  ball ;  then,  on  turning  on  the  battery  current,  the  jar  will  be 
charged  and  discharged  with  great  rapidity,  and  the  snapping  noise  become  continuous ; 
if  a  piece  of  paper  be  held  between  the  knob  of  the  jar  and  the  wire,  it  id  instantly  per- 
forated, but  not  set  on  fire. 

143.  Twist  a  platinum  wire  around  the  knob  of  a  Leyden  jar,  and  bring  its  end  near 
enough  to  the  poles  of  the  coil  to  almost  touch  them  without  quite  doing  so,  and  a 
noiseless  spark  of  feeble  light  will  pass  from  each  pole  to  the  extremities  of  tne  platinum 
wire  ;  if  at  this  moment  the  outer  coating  of  the  jar  be  connected  with  one  of  the  poles 
of  the  secondary  coil,  the  spark,  at  the  interruption  on  that  side  will  suddenly  become 
noisy  and  brilliant ;  what  is  very  singular,  the  noiseless  spark  will  kindle  paper  and 
other  combustibles,  while  the  noisy  flash  will  fail  to  kindle  them. 

1 50.  Charge  a  large  electrical  battery  by  cascade,  the  jars  being  arranged  hori- 
zontally and  in  succession,  the  knob  of  the  first  nearly  touching  the  outside  coating  of 
the  second,  and  so  in  regular  series. 

151.  If  the  Leyden  jir  be  coated  with  spangles,  a  spark  will  appear  at  each  break,  and 
the  whole  jar  be  li t  up  with  hundreds  of  brilliant  sparks  each  time  it  is  charged  and  dis- 
charged. 

1  o2.  When  the  continuous  discharges  from  the  Leyden  jar  are  made  to  pass  through 
the  centre  of  a  large  lump  of  crystals  of  alum,  sulphate  of  copper,  or  ferro-cyanate  of  pot- 
ash, the  whole  of  the  crystal  is  beautifully  lighted  up  during  the  passage  of  the  electri- 
city from  one  wire  of  the  discharger  to  the  other. 

153.  The  chemical  effects  of  the  coil  may  be  shown  by  causing  the  secondary  current 
to  pass  through  a  tube  of  air  hermetically  sealed,  Fig.  241 :  the  Oxygen  and  ^Nitrogen 
combine  to  form  Nitrous  acid,  with  the  production  of  red  fumes. 

1  5  *•.  Enclose  Oxygen  in  a  tube  with  solution  of  starch  and  Iodide  of  Potassium,  Fig. 
242,  r.nlpas  as  iccession  of  sparks  fiom  the  coil,  one  by  one  ;  the  Iodide  of  l'otas.-ium  wiil 
S3oa  bj  decomposed,  and  tae  characteristic  blue  color  resulting  from  t;ie  action  of  starch 
on  free  loline  be  produced,  showing  the  conversion  of  Oxygen  into  Ozone. 

155.  Water  may  be  decomposed  by  connecting  the  poles  of  the  coil  with  two  of  \Vol- 
laston's  dischargers,  consisting  of  platinum  wires  covered  with  glass,  the  tubes  being 
filled  with  mercury  :  Oxygen  and  Hydrogen  will  be  set  free  at  each  pole  alternately,  and 
a  mixture  of  tiie  two  gooses  may  be  collected  iu  an  inverted  glass  test  tube  filled  with 
water. 

156.  The  vapor  of  water  may  be  decomposed  by  passing  a  continuous  charge  from 
the  coil  through  steam  in  a  glass  flask,  and  a  mixture  of  the   two  gases  collected 
in  an  inverted  tube,  Fig.  243. 

157.  If  the  ste*4  wires  from  the  poles  be  applied  to  any  small  animal,  such  as  a  rat, 
or  a  rabbit,  life  will  instantly  be  destroyed  ;  t*'o  of  Bunsen's  cells  are  quite  sufficient. 
With  twelve  of  Bun.sen's  cells  a  man  could   probably  bo  struck  dead.     A  very  feeble 
spark  from  one  small  Grove  or  Bunsen  cell  may  be  transmitted  through  a  large  circle  of 
persons  joining  hands.     These  experiments,   however,  should  be  performed  with  the 
greatest  caution. 

158.  Mi?n3to-Electric   Machines.     The  best  machine  for  exhibiting  the 
effects  of  Magneto-electricity  is  Page's,   Fig.  247.     On  turning  the  wheel  w,  by  mr.-ms 
of  the  ivory  handle  attached  to  it,  the  coils   A  A,  are  made  to  revolve  with  great  r.ipid- 
ity,  and  continuous  currents  of  positive  and  negative  e  ectricity  are  discharged  from 
the  cups  p  and  N,  which,  by   means  of  wires,  may   be  used  for  experiments   ia  electro- 
inagnetism,  decomposition  of  chemical  compounds,  the  production  of  lighf,  and  the  giv- 
ing of  shocks,  in  the  same  manner  as  the  wires  proceeding  from  the  poles  of  a  galvanic 
battery. 

1 59-  This  instrument  may  be  made  to  produce  an  electricnl  current  of  high  or  feeble 
intensity,  by  making  use  of  coils,  consisting  of  very  lo  'g  and  fine  wire,  for  the  former, 
and  of  coils  composed  of  short  and  coarse  wire  for  the  latter  ;  the  former  is  more  useful 
for  shocks  md  chemical  decomposition,  the  latter  for  heating  and  magnetic  effects. 

1 1O.  By  suddenly  breaking  tho  magnetic  current,  a  secondary  current  in  the  same 
direction  of  much  greater  intensity  can  be  induce!  ;  the  breaking  of  the  circuit  is  ac- 
complished by  me  ins  of  a  steel  wire,  thrust  through  the  cup  x,  and  bearing  upon  the 
toothed  wheel  mounted  above  the  pole  changer.  For  giving  shocks,  this  steel  wire  should 
be  inserted  and  firmly  fastened  in  its  place ;  but  for  all  other  experiments  it  should  be 
removed,  and  the  primary  current  used  alone. 

161.  Connect  the  wires  proceeding  from  the  poles  p  and  N,  with  the  extremities  of  a 
galvanometer,  Fi%.  185,  and  the  needle  will  at  once  be  violently  oscillated. 

1 32.  Connect  the  polar  wires  with  the  extremities  of  an  electro-magnet.  F/>s.  1W>, 
196,  208,  and  a  very  considerable  degree  of  magnetic  po.ver  will  be  produced,  quito 


MAGNETO-ELECTRICITY,    TH2HMO-2LECTRICITY. 
k 

sufficient  to  raise  weights,  and  produce  motion  in  some  of  the  most  simple  electro-mag- 
netic machines. 

163.  Connect  the  polar  wires  with  a  telegraphic  line,  and  it  will  be  found  that  mes- 
sages may  be  communicated  by  Morse's  Indicator.  Fig.  199. 

164.  By  connecting  the  polar  wires  with  the  apparatus  represented  in  Fig.  1G2,  wa- 
ter may  easily  be  decomposed,  and  the  Oxygen  and  Hydrogen  collected  in  separate  tubes 
or  in  one  ;  in  the  laWer  case  one  cubic  inch  of  the  mixed  gases  will  be  liberated  in  five 
to  ten  minutes  ;  it  is  found  that  platinum  terminal  wires  answer  better  with  the  mag- 
neto-electric current  thin  strips  of  platinum  foil  for  thn  experiment. 

165.  By  placing  a  piece  of  unsized  paper  iu  the  curved  part  of  the  u  tube,  Fig.  1G4, 
BO  as  to  separate  the  substances  that  are  Set  free  at  the   two  poles,  most  of  the  experi- 
ments upon  the  decomposition  of  saline  solutions  described  under  Expt.  34,  of  the  chem- 
ical effects  of  the  Battery,  may  be  performed.     Sulphate  of  Soda,  Nitrate  of  Potash, 
Iodide  of  Potassium,  Sulphate  of  Copper,  Acetate  of  Le  d,  Nitrate  of  Silver,  Chloride 
of  Gold,  may  be  decomposed,  and  these  medals,  or  their  oxides,  be  obtained  at   the  nt  g- 
ative  pole.     The  etherial  solution  of  Gold  prepared  by  dissolving  a  strong  solution  of  tae 
Chloride  of  Gold  in  Ether,  may  be  substituted  for  the  Chloride  of  Gold  pure. 

166.  If  the  polar  wires  be  connected  with  fine  carbon  points,  Figs.  159,  249,  a  con- 
tinuous light  of  great  brilliancy  will  be  evolved. 

167.  If  the  polar  wires  of  the  magneto-electric  machine  be  attached  to  the  primary 
coil  of  Page's  separable  helices,  or  lluhmkorCFs  coil,  all  the  effects  of  these  instruments 
may  be  obtained  in  the  same  way  as  when  a  galvanic  battery  i.s  employed. 

138.  The  primary  magneto-electric  current  has  too  low  an  intensity  to  afford  strong 
shocks,  but  these  may  be  increased  by  making  use  of  armatures  wound  with  a  greut 
length  of  very  fine  wire.  Secondary  currents,  however,  may  be  obtained  by  interrupt- 
ing the  primary  circuit,  as  in  the  case  of  Page's  separable  helices :  these  have  a  much 
higher  intensity,  and  give  powerful  shocks.  The  primary  current  is  broken  by  means 
of  a  wire  running  from  N,  and  pressing  upon  fie  pins  rising  from  the  circumference  of  a 
wheel  mounted  on  the  axle  of  the  coils.  Fig.  247.  Sec  Expt.  1 30. 

169.  To  show  that  shocks  may  be  obtained  from  the  primary  current,  the  wire  that 
'plays  upon  the  pins  must  be  removed,  so  that  tiie  circuit  may  not  be  broken  ;  tho 

springs  pressing  on  the  pole-changer  must  neither  of  them  leave  the  segment  which  it 
touches  before  it  comes  in  contact  with  the  oppo  ite  segment ;  otherwise  the  circuit  will 
be  broken  at  the  pole-changer,  an  1  strong  secondary  shocks  obtuiued.  Metallic  hrmd.cs 
are  then  to  be  connected  by  means  of  wires  with  the  cups  p  and  N,  and  the  coils  set  i.i 
motion :  slight  shocks  will  immediately  be  exper.enced.  These  may  be  partially  reg- 
ulated by  varying  the  speed. 

170.  To  exhibit  the  shocks  produced  by  the  secondary  current,  the  wire  leading  from 
'N,  and  pressing  upon  the  pins  of  the  horizontal  wheel  must  be  inserted,  and  tue  coils 

set  in  motion.  Whenever  the  wire  is  in  contact  with  the  pins,  the  primary  current 
passes  from  r,  through  the  magnets  and  axis  of  the  instrument,  by  the  pins  and  con- 
necting wire  to  the  cup  N,  in  preference  to  passing  through  the  body  of  the  subject. 
But  iis  soon  as  the  wire  ceases  to  press  upon  the  pins,  the  primary  current  is  broken, 
and  the  same  instant  a  secondary  current  of  great  intensity  is  induced,  which  is  in  the 
same  direction  with  the  primary  current,  and  not  being  able  to  traverse  the  instrument, 
is  compelled  to  pass  through  the  body  of  the  operator,  giving  a  sho<  k  of  extreme  inten- 
sity, increasing  with  the  velocity  of  revolution ;  the  hands  cannot  be  unclo? ed,  and 
with  a  powerful  machine,  the  person  through  whom  it  is  discharged  is  prostrated,  rolls 
on  the  ground,  and  is  at  the  mercy  of  the  operator.  At  the  same  time  bright  sparks  of 
light  sometimes  a  i  inch  in  length,  will  flash  between  the  pins  and  the  wires. 

171.  The  shocks  may  be  regulated  by  varying  the  speed  of  revolution ;  also  by 
placing  an  iron  armat.jre  across  the  steel  magnets,  neutralizing  their  power ;  also  by 
passing  the  primary  current  through  a  piece  of  wet  cotton  wickjng,  one  end  of  which  is 
connected  with  one  of  the  poles,  p  or  N,  and  the  other  attached  by  a  wire  to  one  of  the 
metallic  handles.     The  handles  are  sometimes  one-half  of  wood ;  no  shock  is  felt  when 
either  one  handle  or  both'is  held  by  the  wooden  portion.     Sometimes  the  handle  is  made 
of  glass  or  porcelain,  tipped'with  moistened  sponge  ;  in  this  case  no  shock  is  felt  when 
the  handle  is  held  by  the  glass.     The  arm  connected  with  the  negative  cup  will  be  most 
affected  by  the  shocks. 

1  72,  Thsrmo-Electricity.  Place  a  bar  of  copper  Upon  a  bar  of  bismuth,  in  the 
'manner  represented,  Fig.  258,  and  npply  a  lamp  at  the  point  of  junction  a  current  of 
electricity  will  be  produced  circulating  as  represented  in  the  figure. 

173.  Instead  of  heat  apply  cold  at  the  point,  o,  and  an  electric  current  in  the  oppo- 
site direction  will  be  induced  as  indicated  by  the  motion  of  the  needle. 

1 74.  Construct  a  battery  of  several  pairs  of  plates  of  Antimony  and  Bismuth,  as  re- 
presented  in  Fig.  260,  and  observe  the  great  increase  of  effect. 

175.  With  a  Thermo-electric  multiplier,  which  may  now  be  procured  of  any  Philo- 
-seph>al  instrument  maker,  observe  the  extreme  delicacy  with  which  slight  change  of 

temperature  are  indicated. 


EXPERIMENTS    ON    GALVANISM.  543 

176.  With  Farmer's  Thermo-electric  battery,  repeat  the  various  experiments  de- 
scribed above,  in  connection  with  the  galvanic  battery;  for  the  purpose  of  illustrating 
its  decomposing,  magnetic,  illuminating,  and  physiological  power :  also  use  it  instead 
of  tae  battery  to  actuate  Page's  and  ituhmkorif  s  Coils. 

1/7.  Instead  of  applying  heat  transmit  a  current  of  electricity  through  a  thermo- 
electric series,  consisting  of  antimony  and  bismuth.  Cold  wiil  be  produced  at  the  first 
junction,  and  heat  at  tae  second  If  tue  electric  current  be  transmitted  in  the  same 
direction  wita  the  thiruio  electric  current,  heat  is  the  result;  if  m  the  contrary  direc- 
tion cold  will  be  produced. 

173.  Animil  Electricity.  The  electric  current  existing  in  the  animal  economy 
and  circulating  from  the  interior  to  the  exterior  of  a  muscle,  may  be  shown  by  arranging 
a  series  of  limbs  of  frogs  in  such  a  manner  that  the  interior  of  one  will  come  into  contact 
with  the  exterior  of  the  next,  so  that  one  of  the  extremities  of  the  series  is  formed  of 
the  interior  of  the  muscle,  while  the  other  is  formed  of  the  exterior  ;  the  terminal  pieces 
should  dip  into  cavities,  in  which  a  little  distilled  water  is  placed.  On  introducing  the 
wiras  of  a  galvanometer  into  these  cavi  ies,  and  completing  tue  circuit,  a  current  is 
produced  by  which  the  galvanometer  needle  is  deflected,  iodide  of  potassium  is  decom- 
posed, and  the  leaves  of  an  electroscope,  with  the  aid  of  a  condenser,  made  to  diverge. 

173.  The  same  current  may  also  be  shown,  by  stripping  the  flesh  from  the  upper  end 
of  a  frog's  leg,  so  as  to  display  the  nerve,  and  then  dipping  the  extremity  of  tae  nerve 
into  one  vessel  of  acidulated  water,  and  the  foot  of  the  frog  into  another,  and  then  con- 
necting the  two-  vessels  of  water  by  means  of  a  curved  wire  ;  as  soon  as  the  circuit  is 
completed,  the  leg  of  the  frog  is  perceptibly  convulsed. 

1 3D.  A  frog's  leg  miy  be  used  as  a  g ilv  moamfer,  by  stripping  down  the  flesh  so  c,s  to 
expose  the  nerve,  and  then  inserting  tae  resf  of  the  limb  in  a  small  glass  tube,  the 
ne/ve  hanging  out:  whenever  an  electric  current,  however  slight,  is  made  to  pass 
through  the  nerve,  the  leg  H  immediately  convulsed  :  it  is  said  that  such  an  arrange- 
ment is  50,OJO  times  more  delicate  tain  the  most  delicate  gold  leaf  electroscope. 

131.  Paysiotojioil  fifasts  of  tia  Cirraio.     Expose  the  nerve  of  the  leg 
of  a  frog,  and  twist  a  bit  of  copper  wire  around  a  piece  of  zinc  ;  then  touch  the  nerve  wita 
the  zinc,  and  the  outside  of  the  leg  with  the  copper  :  at  the  moment  of  contact  the  leg  is 
convulsel ;  disconnect  the  t.vo  matils,  and  the  convulsions  cease,  though  they  may  still 
be  in  contict  with  the  animal.    Each  time  the  zinc  and  copper  are  made  to  touch,  the 
convulsions  are  renewed. 

132.  Place  a  live  Bounder  01  a  plate  of  zinc  or  pewter;  and  bring  a  silver  spoon  in 
contact  with  its  back;  there  will  be  no  convulsion,  but  if  the  spoon  be    made  to  touch 
the  plate  while  it  rests  on  the  tHh,  tie  animil  beco:nes  strongly  convuNel. 

133.  If  a  piece  of  silver  be  placed  above  the  tongue,  and  a  piece  of  zinc  beneath  it, 
no  sensation  is  perceived  so  long  as  the  metals   are  separated,  but  if  they  touch  each 
other,  a  peculiar  tingling  sensation  or  taste  is  experienced.     If  tho   silver  be  placed 
between  the  upper  lip  and  the  teeth,  instead  of  under  the   tongue,  a  flash  of  light  will 
appear  before  the  eyes. 

131.  A o  p  a, rat  a *.  The  apparatus  for  the  performance  of  the  experiments  described 
in  this  work,  may  be  obtained  of  the  following  Philosophical  instrument  makers  :  E  S. 
Ritchie,  N.  B.  Chamberlain,  Boston;  B.  Pike  &  Sous,  New  York;  W.  Y.  McAllister, 
Philadelphia. 

*  LI .IUI  A  .{  , 

,  V  KUSITY    OF 

VIRG.  GE  JR.  II ,  4  0. — " 


FINI9. 


INDEX. 


2f.  B. — The  Numbers  refer  to  the  Pages. 


A. 

ABSORPTION  of  heat,  56. 

»«  "        in  ebullition,  128. 

Action  of  the  same  current  on  successive 

chemical  solutions,  359. 
Air,  compression  of,  evolves  heat,  225. 
"     specific  heat  of,  219. 
"     expansion  of,  by  heat,  93. 
"    weight  of,  ti. 
"     thermometer,  101. 
Aldebaran   spectrum  of,  265,  275. 
Amalgam  for  electrical  machine,  311. 
Amount  of  vapor  formed  proportionate  to 

temperature,  17«. 
Ampere's  theory  of  magnetism,  331. 

'i  "         supported   by  magneto- 

electric  induction,  449 
Animal  electricity,  511. 
Anomalous  effect  of  heat  on  water,  9o. 
Apparatus.  543. 

Applications  of  electro-magnetism  to  mo- 
tion, 409. 

Applications  of  expansion  by  heat,  80. 
Arago's  rotations,  44ti. 
Arc,  voltaic,  345. 

"     influence  of  magnetism  on,  505. 
Arcturus,  spectrum  of,  Go,  275. 
Ascension  of  heated  liquids  and  gases,  41. 
Astatic  needle,  371 

•'      galvanometer,  379. 
Atlantic  telegraph  cable,  403. 

battery,  403. 
"  "        history  of,  408. 

signal  instrument,  406. 
"  "        rate  of  transmission  by, 

407. 
Atmosphere,  peculiar  properties  of,  5. 

B. 

BATTKRIFS,  Cruikshanks,Bunsen's,Grove's, 

Danieirs.  Smee's,  331-337.  _ 
Batteries,  management  of,  837. 
Batteries  of  quantity  and  intensity,  '80. 
Peltegeux,  spectrum  of,  2»i5,  275. 
Bismuth  an  eminently  dia-magnetic  sub- 
stance, 373. 

Black,  Dr.  Joseph,  the  discoverer  of  the 
Laws  of  Latent  Heat,  124. 
discoverer   of   absorption   of   heat   in 
vaporization,  and  evolution  in  con- 
densation, 130. 


Black  Dr.  Joseph,  account  of  the  succes- 
sive steps  in  the  improvement  of   the 
Steam  Engine,  141. 
Boiler  of  the  steam  engine,  146. 
Boiler  of  locomotive,  1*2. 
Boiling  point   influenced  by  atmospheric 
pressure,  131. 

measurement  of  heights  by,  132. 
influence  of  adhesion  on,  133. 
influence  of  air  in  water  on,  134. 
influence  of  solids  in  solution  on,  134. 
raised    by    increase  of   pressure,   aud 

lowered  by  diminution,  134. 
Breguefs  metallic  thermometer,  110. 
JJimsL-u's  Battery,  33T. 

C. 

CAESIUM,  269. 

Caillaud's  Battery,  397. 

Caioresceuce  of  rays  of  heat,  74. 

Calorimeter  of  l^avoisier  and  La  Place,  214. 

Capella,  spectrum  of,  2oo,  275. 

Camera,  photographic,  283. 

Carbonic  acid,  solidification  of,  196. 

Carre's  Ice  Machine,  204. 

Change   of   density   produces    change    of 

temperature,  221. 
Charges  for  batteries,  531. 
Chemical  constitution  of  water,  319. 
"        effects  of  the  battery,  348. 
"        rays,  range  of,  in  solar  spectrum, 

Fluorescence,  259. 
"        rays  of  the  solar  beam,  258. 
Chemistry,  origin  of  name,  1. 
•  "  nature  of,  1. 

"  a  science  of  experiment,  9. 

"  differs  from  >.utural   Philoso- 

phy, 8. 

connected  with  tho  Arts,  10. 
medicine  and  agriculture.  11. 
"  depends  upon  the  balance.  14. 

fundamental  princ  iple  of,  15. 
active  agents  of,  19. 
Circuit  breaker.  452. 

Circumstances  influencing  evaporation.,181. 
Cold  produced  by  evaporation,  181. 
Compensation  pendulums,  88. 
Compound  nature  of  light,  253. 
Condensation  of  steam,  139. 
Condensing  steam  engine,  143. 
Condenser,  attached  to  lluhuikorff's  coiL 
456. 

i 


CON 


545 


EXT 


Convection  of  heat  in  liquids,  37. 
'•  in  gases,  33. 

Convertibility  of  forces,  and  indestructi- 
bility ,  2.44. 

Copper  piat»  of  the  battery,  part  played 
by,  320. 

Copper  sheathing,  protection  of,  363. 

Crown  of  cups,  Volta's,  330. 

Cruikshank's  battery,  331. 

Cr^ophorus,  184 

Culinary  paradox,  137. 

D. 

DAGUERREOTYPE  process,  280. 

Dalton's  law  of  the  tension  of  vapors,  174. 

Daniell's  battery,  333. 

hygrometer,  189. 
pyrometer,  110. 

Davy,  Sir  H.,  extraordinary  galvanic  ex- 
periment, 358. 

the  discoverer  of  the  electric  light,  346. 
Decomposition  of  water  by  the  battery ,  350. 
Decomposing  tube,  35 1. 
Decomposition  of  metallic  salts.  353. 

of  metallic   oxides   by   the 

battery,  £52. 
of  water,  350. 
De  la  Rive's  ring,  384. 
De  Luc's  pile,  339 
Despretz'  experiments  upon  the  conversion 

of  Carbon  into  diamond,  477. 
Dew,  how  produced,  191. 
Dia  magnetism  of  gases,  373. 
Dia-thermancy  of  solids,  61. 

of  liquids,  64. 
"  of  gases,  65. 

Difference   between   galvanic  and  statical 

electricity,  341.  500. 
Different  kinds  of  heat.  66. 
Directive  action  of  the  earth,  370. 
Disappearance  of  heat  in  liquefaction,  113. 
Distillation,  164. 
Double  refraction  and  polarization  of  heat, 

of  light,  252. 

Draught  of  chimneys,  93. 
Duboscq's  electric  lamp,  345. 

E. 

EARTR  a  part  of  the  telegraphic  circuit,  398. 
Ebullition,  127. 

Elastic  force  of  vapor,  varies  with  tempera- 
ture, 174. 
Elastic  force  of  vapor  in  two  connected 

vessels,  that  of  the  colder,  177. 
Flement,  definition  of,  16. 
Electricity,  nature  of,  290 

two  theories  of,  300. 
"  two  kinds,  Vitreous  and  Resin- 

ous, 293- 
"  statical.  289. 

galvanic,  311. 
"  sources  of,  291. 

*          effects  of,  307. 


Electricity,  induction  of,  296. 

"  of  the  machine  distinguished 

from  that  of  the  battery,  500. 

"  and    magnetism,  effect  of   on. 

light,  504 

"  induced   by  induced  magnet- 

ism, 440. 
"  induced  by  the  magnetism  of 

the  earth,  448. 
Electric  gas-lighting,  420. 

lire  alarm,  417. 

"       light,  not  produced   by  combus- 
tion, 346. 
lamp,  346. 
"       telegraph,  387. 
Electrical  insulation,  '294. 
'•         machine,  301. 

tension  exists  before  the  passaga 
'     of  the  current,  823. 
Electrified  bodies  repel  each  other,  293. 

"      attract  each  other,  L93. 
Electro-magnetism,  367 

laws  of,  381. 

"  experiments  on,  532. 

magnets,  376. 
"       magnetic  clocks,  415. 

"         locomotives,  412. 
"       motor  of  Froment,  410. 
"       positive  and  negative  bodies,  361. 
Electrophorus,  305. 
Electroscope,  293. 
Klectrotyping,  364. 

Electro-chemical  order  of  the  elements,  361. 
Equatorial  magnetic  position,  373. 
Evaporation,  169 

"  of  different  liquids,  different, 

179. 

"  in  a  vacuum    is    instantan- 

eous, 172. 

Expansion  produced  by  heat,  79. 
"  of  liquids,  91. 

of  gases,  92. 

"  of  water  in  vaporization,  138. 

Expansive  power  of  steam  increases  with 

temperature,  155. 
Expense   of  electro-magnetism    compared 

with  steam,  414. 

Experiments   on    conduction,   convection, 
radiation,  and  transmission  of  heat,  76. 
on  effects  of  heat, — expansion  of  solids, 

liquids,  and  gases,  110. 
on  liquefaction,  125. 
on  vaporization  and  steam,  167. 
on  evaporation,  209. 
on  specific  heat,  231. 
on  sources  of  heat,  237. 
on  light,  287. 
on  electricity,  310. 

on  gal vanfsm,  electro-magnetism, mag- 
neto electricity,     thermo  electricity, 
animal  electricity,  531. 
Experiment  of  the  three  cups,  357. 
Explosions  of  steam  boilers,  150. 

"         explained  by 
the  spheroidal  state,  162. 
Extra-current,  433. 


FAH 


546 


HtTA 


F. 

FAHRENHEIT'S  scale,  105. 

"      reduced  to  Centigrade 
and  Reaumur,  107. 

Faraday's  discovery   of  Volta  electric  in- 
duction, 425. 
discovery  of  induction  of  electricity  by 

electro  magnetism,  444. 
discovery  of  the  effect  of  magnetism  on 

polarized  light,  506. 
Farmer's  thermo  electric  battery,  516. 
Fire-syringe,  225. 

Fizeau's  discovery  of  the  effect  of  the  con- 
denser upon  Ruhmkorff  's  coil,  457. 
Flame,  dia  magnetism  of,  505. 
Fluidity,  heat  of,  116. 
Fluorescence,  £59. 
Fluxes,  121. 

Foci  for  heat,  light,  and  chemical  rays  dif- 
ferent, 261. 

Force  of  expansion  by  heat,  82. 
Forces,  indestructibility  and  convertibility 

of,  244,  5£. 

Fraunhofer's  lines  in  solar  spectrum,  263. 
explained  by  Kirchhoff,  271. 
displayed  upon  a  screen,  265. 
instrument  for  observing,  264. 
Freezing  mixtures,  119. 

"         of  water  in  vacuo,  183. 

of  water,  anomaly  in,  98. 
"         point  of  water  lowered  by  salts 

and  acids,  12 ». 

of  water,  heat  evolved  by,  117. 
"         of  mercury  in  red  hot  crucible. 

199. 

Friction  a  source  of  heat,  235. 
Frog  battery,  519. 

"     Galvani's  experiment  on,  313. 
Froment's  electro-motor,  410. 
Fuel  not  economized  in  using  other  liquids 
than  water,  158. 
not  economized  in  boiling  water  at  a 

low  temperature,  15'>. 
Fusing  point,  why  fixed,  116. 

"         "      of  different  substances,  113. 

G. 

GAIVANI'S  theory,  312. 

Galvani  the  discoverer  of  galvanism,  312. 

Galvanism,  discovery  of,  312. 

Galvanic  electricity,  3 II. 

Galvanic  electricity  produced  by  chemical 

action  317. 
Galvanic  battery,  329. 
Galvani  -.  batteries  of  historic  note,  341. 
Galvanometer,  3/8. 
Gases,  dia-magnetism  of,  373. 

''      dia-thermancy  of,  65. 

"      expansion  of,  by  heat,  92. 

"      nature  of.  194. 

liquefaction  of,  194. 
peculiar  properties  of,  5. 
constitution  of,  '94. 

"      poor  conductors  of  heat,  34. 

"       liquefaction  of,  194. 

"      solidified,  199. 

23 


Gas  battery,  327. 
Geissler's  tubes,  469. 

"  "       applications  of,  472. 

Globe,  constitution    of,  dependent    upon 

temperature,  2l»8. 
Graduation  of  thermometers,  105. 
Grove's  Nitric  acid  battery,  335. 

"       gas  battery,  3^7. 
Grove  on  the  correlation  of  Forces,  529. 
Gymnotus,  517. 


II. 


HARRISON'S  compensation  pendulum,  88. 
Heat,  nature  of,  22,  !i37. 
"     seeks  an  equilibrium,  25. 
"      conduction  of.  in  solids,  26. 
;      the  cause  of  evaporation,  169. 
"     explained  on  the  mechanical  theory, 

241. 
"      light  and  chemical  effect,  relations 

of,  in  the  solar  spectrum   287. 
<{     of  the  battery  and  mechanical  equiv- 
alent of  heat,  317. 
1      produced  by  motion,  235. 
41     converted  into  light  243. 
1     rays  of  solar  beam,  258. 
'     sources  of.  232. 
"     evolved  in  solidification,  117. 
"      latent,  112,  115. 
'      specific,  210. 
1      produces  expansion,  79. 
"     radiation  of,  effect  of  surface  on,  43. 
'      reflection  of,  48. 
'     refraction  of,  67. 
1      double  refraction  of,  75. 
"     in  voltaic  circuit,  Favre's  experiment, 

347,  517. 
"     evolved  in  condensation  of  steam, 

129. 

"      latent  in  steam,  128, 145. 
"      specific  of  solids,  216. 
11          "       liquids,  216. 
"          "       gases,  217, 218. 
•'          "       Rejfnaulfs  table  of,  219. 
"          "       altered  by  change  of  density, 
220;   diminished  by  com- 
pression ;  increased  by  ex- 
pansion, 221. 
'      conduction  of.  in  liquids,  33. 

"  of.  in  gast-s,  34. 

"      convection  of,  in  liquids,  37. 
«  '"  "      gases,  38. 

"      propagation  of,  through  liquids,  40. 
'     reflection  of,  by  fire-places,  55. 
"     absorption  of,  affected  by  color,  57. 
"     Melloni's  apparatus    for  measuring 

small  degrees  of,  63,  514. 
"     rays  of  solar  beam,  unequal  refran- 
gibility  of,  Sir  H.  Englefield  a  ex- 
periments, 68. 

1     Sir  W.  Herschel's  experiments,  69. 
"     experiments   on  conduction,   radia- 
tion, reflection,   transmission,  ef- 
fects of,  110. 

Heated  particles  of  liquids,  their  ascension 
how  explained,  41. 


HEA 


547 


MAG 


Heating  effects  of  galvanic  battery,  343. 
Henry's  coils,  436. 

"        discoveries  in  electro-magnetism, 

421. 

in  telegraphy,  422. 
"         of  the  extra-current,  438. 
High  pressure  steam-engine,  142. 
History  of  Atlantic  telegraph,  408. 

"        of  discovery  of  induction  of  elec- 
tricity by  electro  magnetism,  444 
"        of   discovery   of   magneto-electric 

induction,  442. 

"        of  discovery  of  extra  current,  438. 
"        of  discovery  of  electro-magnetism, 

421. 

"        of  discovery  of  Yolta-electric   in- 
duction, 425. 

"        of  discovery  in   the  construction 
of  induction  coils,  and  magneto  - 
electric  machines,  508. 
"        of  the  theory  of  the  correlation  of 

the  Physical  Forces,  529. 
Holmes'  magneto-electric  machine,  488. 
Horse  shoe  electro  magnets,  386. 
Hydro-electric  machine,  306. 
Hydrogen,  how  transferred  within  the  bat- 
tery, 319. 

cooling  effect  of,  on  red-hot  wire,  36. 
Hygrometer,  Daniell's,— Saussure's,  189. 

I. 

Ice  Machines,  204,  227. 
Ice,  specific  heat  of,  217. 
Indium,  259. 
Induction,  theory  of,  298. 

"         on  the  approach  and  removal 

of  the  primary  current,  429. 
"         conditions  of,  431. 
"         takes  place  through  a  consid- 
erable distance,  427. 
"         coils,       Page's,       Ruhmkorff's 

Ritchie's,  450,  454,  460. 
1 '          of  magnetism ,  3  72. 
Insects,  temperature  of,  measured,  515. 

J. 

Jacoby's  electro-motor,  412. 
Joule's  Law,  236 

Joule,  experiments  of,  on  mechanical  equi- 
valent of  heat,  236. 

K. 

KirchhofTs  discovery  of  the  coincidence 
between  the  dark  lines  of  the  solar  spec- 
trum and  the  bright  lines  of  metallic- 
spectra,  271. 

L. 

Ladd's  magneto-electric  machine,  497. 
Land  and  sea  breezes,  39. 
Latent  heat,  210. 

"        "     of  condensing  engine,  145. 
Law  of  chemical  decomposition  by  the  bat- 
tery, 361. 


Leyden  jar,  302. 

"        "     charged  by  Ruhmkorff's  coll, 

463 
'     by    Page's    separable  helices, 

Light,  nature  of,  246. 
"      sources  of,  247. 
"      reflection  of,  250. 
"      refraction  of,  251. 
;      double  refraction  of,  252. 
1      solar,  compound  nature  of,  253. 

"  number  of  vibrations  required 
to  produce  the  different  col- 
ors, 256. 

"        "     heat  rays  of,  256. 
"•        "    chemical  rays  of,  258. 
"        "     decomposition  of,  2;~>4. 

'     triple  character  of,  260. 
"        "     spectrum  of,  crossed  by  dark 

lines,  263. 
"        "     spectrum  of,  crossed  by  bright 

lines,  273. 

"    effect  of,  on  plants,  277. 
;<     effect  of,   on    chemical    com- 
pounds, 279. 

"     on  daguerreotype  plates,  280. 
"    on  photograph  paper,  284. 
"        "     relations  of  the  rays  of  heat  to 
those  of  light  and  chemical 
effect,  287. 

"      experiments  on,  287. 
ft      artificial,  spectra  of.  262. 
"      of  magneto  electric     machine    ap- 
plied to  illumination.  487- 
"      brilliancy    of    that     produced  by 
Wilde's    magneto-electric    ma^ 
chine,  494. 

"      of  the  voltaic  arc,  347. 
"      effect  of  electricity  and  magnetism. 

on  504. 
"      of  Ruhmkorff's  coil  affected  by  the 

magnet,  471. 

"      comparative  cost  of  producing  by 
Smee's  battery,  Groves's  by  illu- 
minating gas,  the  magneto  elec- 
tric machine,  517. 
Lightning,  spectra  of,  276. 
Liquefaction  produced  by  heat,  113. 

"•          always  attended  by  reduction 
"          of  temperature,  118. 
Liquids  poor  conductors  of  heat,  33. 

"      peculiar  properties  of,  4. 
Luminous  effects  of  galvanic  battery,  344. 


M. 


Magic  circle.  387. 

Magnet  described,  369. 

Magnetic  and  dia-magnetic  bodies,  372. 

needle,  influence  of  the  battery  cur- 
rent on,  368. 

needle  acted  upon  by  the  liquid  part 
of  the  circait,  3Su. 

poles,  mutual  action  of,  370. 

effects  of  the  battery,  367 
Magnet,  influence  of,  on  the  voltaic  aro.  504 


MAG 


548 


SAN 


Magnetism  of  a  helix  carrying  a  current, 
332. 

of  the  earth  affects  the  wire  carrying 

the  current,  385. 
Magnetic  curves,  4*8. 
"       field,  3.3. 

"        poiarizttioa  of  light,  494. 
"        telegraph,  38<". 
Magneto-electric  induction,  439 

"      electricity  used  in  the  arts,  485. 
,  electric  machines.  477. 

electricity  applied  to  the   illumina- 
tion of  iig. it-houses,  487. 
Management  of  batteries,  337. 
MAP  of  solar  spectrum,  263,  270, 
Mircet's  appiratus,  133. 
Material  taeory  of  heat,  237. 
Matter  indestructible,  15. 

"     jtaree  principal  states  of,  3. 
Measurement  of  heights  by  boiling  point, 

Mechanical  theory  of  heat,  239 

"          equivalent  of  heat,  23">. 
Melloni's  researches  on  heat,  6J,  (33,  64, 5l4. 

thermo  multiplier,  514. 
Mercury,  specific  heat  of,  212. 

u        frozen  in  red-hot  capsule,  164. 
Metals,  relative  conductivity  of,  for  heat.  27. 
conductivity  of,  for  electricity,  28. 
taerino  electric  order  of,  512. 
deposited  from  their  solutions,  353. 
discovered  by  spectrum  analysis,  26d. 
Metallic  connection  between  the  plates  not 
.    neoessary  for  galvanic  action,  3^6. 
Meteors,  spectra  of,  276. 
Mirrors  parabolic,   effect   of,   on    rays   of 

ligat,  5). 
Molecular    movements   in   magnetization, 

3tS. 

Moon,  spectra  of,  275. 
Morse's  telegraphic  indicator,  390. 
"          alphabet,  3J2. 
Motion  produced  by  heat,  239. 
Muscular  electric  current,  518. 

N. 

NATTERER,  process  for  liquefying  gases,  200. 

Nebulae,  spectra  of,  276. 

Nicholson  and  Carlisle,  their  discovery  of 
the  decomposition  of  water  by  the  bat- 
tery, 348 

Nitrogen,  spectrum  of,  470. 

Nobili's  Thermo-electric  battery,  513. 

0. 

OXYGEN,  a  magnetic  substance,  374. 
P. 

PAGE'S  electro-magnetic  locomotive,  412. 

''      pole  changer,  484. 

'"      magneto  electric  machine,  483. 

"      separable  helices,  450. 
Papin's  digester,  159. 
Phosphorus  a  dia-magnetic  body,  373. 
Photography,  281. 


Photographs  produced   by  the    chemical 

rays  of  the  solar  beam,  ^8*. 
f'hysiological  effects  of  tae  battery,  520. 
Plate  electrical  mac  bine.  3' '2. 
Poinc.?  of  resemblance  between  static  and 
gdivauic  electricity,  340,  5u2. 

of  difference,  3-il,  483,  5UO. 
PolartzatioH  of  heat,  75. 
'•  of  light,  152. 

"  and  transfer  of  the  elements 

necessary   for  galvanic   ac- 
tion, 321. 

Poles  of  voltaic  battery,  307,  321. 
Positive  and  negative  poles  of  the  battery, 

how  determined,  34(J. 
Potassium,  spectrum  of,  270. 
Pressure,  how  transmitted  from  boiler  to 

cylinder,  15'>. 

Prism,  its  effect  on  the  solar  beam,  253. 
Procyon,  spectrum  of,  26o,275. 
Progress  of  discovery  in  galvanic   induced 
electricity,  and  induction  coils,  5u8. 

of  discovery  in  electro-magnetism,  421. 
Propagation  of  pressure  through,  fluids,  149. 
Pulse  glass,  188. 
Pyrometer,  Daniell's,  110. 

R. 

RADIATION  of  heat,  42. 

Itain  and  snow,  production  of,  explained, 

226. 

Reaumur's  thermometer,  106. 
Reflection  of  light,  250. 

•'          of  heat,  48. 
Reflecting  galvanometer,   Thomson's,  390, 

3i»2,  404,  406. 

Register  thermometers,  108. , 
Removal  of  atmospheric  pressure  hastens 

evaporation,  183. 
Refraction  of  'ight,  251. 
Refractory  substances,  121. 
Refrangibility  of  heat,  alteration  in,  74. 

of  light,  alteration  in,  259. 
Retardation  of  telegraphic  signals,  402. 
Ritchie's  improved  Kuhmkorff's  coil,  460. 
Ruhmkorff's  coil,  induction  coil,  454. 
mechanical  effects  of,  464. 
physiological  effects,  464. 
heating  effects,  464. 
1  luminous  effects,  467. 
chemical  effects  of,  475. 
dissected,  454. 

decomposition  of  steam  by,  476. 
conversion  of  carbon  into  diamond,  477. 
Rumford's  experiments,  on  heat  of  friction, 
242. 
experiments  on  conducting  power  of 

materials  used  for  clothing,  29. 
Rubidium,  269. 

S. 
SALTS,  effect  of,  in  lowering  freezing  point, 

effects  of,  in  raising  boiling  point.  134. 
Sand  battery,  398. 


SAU 


549 


THE 


Saussure's  hygrometer,  1?9. 

Saxton's  magneto-electric  machine,  480. 

Secondary  induced  currents  of  electricity, 

423. 
"        decomposition  by  the  battery, 

355. 

Sheathing  of  ships,  how  protected,  366. 
Siemens'  magneto-electric  macliiue,  496. 
Sirius,  spectrum  of.  275. 
Smee's  battery,  337. 
Sodium,  spectrum  of,  270. 
Solar  light,  effect  of,  on  plants,  278. 

"        "'        "      ou  chemical  compounds, 

279. 

Solids,  peculiar  properties  of,  4. 
Solidification  evolves  heat,  117. 

"  of  carbonic  acid,  196. 

Sources  of  heat,  232. 
Spark  obtained  from  magnet,  441. 
Specific  heat,  210. 

"         "     determined  by  mixture,  211. 
"         "     determined  by  rate  of  cooling, 

213. 

"        "     determined  by  time,  212. 
"        <k    of  gases,  determined  by  Rcg- 

nault,  219. 

"         "     determined  by  ice  melted,  214 
"        "    altered  by  alteration  of  phys- 
ical stale,  221. 

<;        "     altered  b>-  alteration  of  den- 
sity,^. 

"        "     of  solids,  216. 
"         "     of  liquids,  216. 
"         "     of  water,  216. 
"        "     of  gases,  217. 
Spectra  of  the  Nebulae  crossed  by  bright 
lines,  235,   276. 

of  Potassium,  Sodium,   Caesium,  and 
Rubidium,   compared    with   Fraun- 
hofer's  linos.  270. 
of  artificial  light  and  colored  flames. 

282. 

projection  of, on  screen,  265. 
Spectroscope,  268. 
Spectrum-analysis,  266. 

"  ''          made  by   Ruhmkorff's 

coil,  473. 

Spheroidal  state,  160. 
Stars,  spectra  of,  2  5. 
Statham's  fuse,  466. 
Steam,  latent  heat  of.  130. 
"      elastic  force  of,  133. 
"      used  expansively ,  155. 
"      temperature  of,  at  different  press- 
ures, 156. 

"      electricity  of,  306. 
"      engine,  the  invention  of,  by  Watt, 

141. 

"      condensation   of,  in  condenser,  its 
invention  described  by  Watt,  179. 
"      engine,    condensing  .and    r.on  con- 
densing,    how     distinguished, 
142. 

"      super  heated,  158. 
Still,  for  distillation,  164. 
Submarine  telegraphic  cables,  4r3. 
Sulphate  of  copper  battery,  332. 


T. 


TABLZ  of  conducting  power  for  heat,  27. 
conducting  power  for   heat  compared 
with   conducting   power  for  electri- 
city, 28. 

of  Mclloui,  showing  the  amount  of  heat 
from  different    sources,    transmitted 
by  different  substances,  60. 
of  Melioni,  showing  the  amount  of  heat 
from  the  s;  me  source  that  is  trans- 
mitted by  different  substances,  €3. 
showing  the  different  temperature  of 
the  rays  of  heat  of  different  rofran- 
gibility  contained  in  the  solar  spec- 
trum, 69. 

of  relative  expansion  of  different  sol- 
ids, 82. 

of  Regnault,  showing  the  pressure  of 
steam  at  different  temperatures,  156. 
of  Regnault,  showing  the  sum  of  sensi- 
ble and  latent  heat  in  steam  at  differ- 
ent temperatures,  157. 
of  Regnault,  showing  the  elastic  force 
of  watery  vapor  at  different  temper  • 
atures,  177. 

of  density   of   vapors  at   the  boiling 
points   of   their    liquids,    compared 
with  that  of  air,  18U. 
of   temperatures    at    which    different 

gases  solidify,  199. 
of  specific  heat  of  solids  of  equal  weight 

between  32°  and  211°,  21o. 
of  specific  heat  of  liquids,  217. 
of  Delaroche  and  Eerard,  of  specific 

heat  of  gases,  218. 
of  Reguault,  of  specific  heat  of  gases-, 

219. 

of  rise  of  specific  heat  with  rise  of  tem- 
perature, J£il. 

of  heat  produced  by  various  combusti- 
bles, 234. 
of  electro-negative  and  electro-positive 

bodies,  351. 
of  magnetic  and  dia-magnetic  bodies, 

375. 

of  Morse's  telegraphic  alphabet,  392. 
of  velocity  of  telegraphic  current,  401. 
of  direction  of  induced  currents  up  to 

the  ninth  order,  4fe8. 
comparative  cost  of  light,  517. 
Transfer  of  solids  in  voltaic  arc,  3i5. 
Tangent  galvanometer,  3i9. 
Telegraph,  magnetic,  387. 
Telgraphic  batteries,  396. 

"          manipulator,  392. 
"          relay ,  393. 
Temperature,  increase  of,  with  increase  of 

depth  beneath  the  surface,  233. 
Thallium,  269. 

Thomson's  reflecting  galvanometer,  405. 
Thermo-chrosis,  or  calorific  tint,  72. 
"        electric  battery,  512. 
"        electricity,  510. 
"        multiplier  of  Melloni,  614. 
Thermometers,  100. 

"  Breguet's  metallic,  110. 


THE 


550 


WOL 


Thermometers,  Fahrenheit,  105. 

<"  Centigrade,  106. 

"  Keaumur,  106. 

*'  maximum   and  minimum, 

109. 

««  Rutherford's     self-register- 

ing, 109. 

"  comparison  of  various  scales 

of,  107. 

"  graduation  of,  105. 

"  tests  of  accuracy  of,  105. 

Torpedo,  513- 
Transmission  of  heat,  57. 

'•  of  telegraphic  messages,  395. 

Triple  character  of  solar  light,  260. 


U. 


URANIUM  glass,  468. 

V. 

VALVES  of  steam-engine,  153. 

Vaporization,  123. 

"Vapor,  amount  of,  in  the  air,  188. 

"      in  the  atmosphere,  affects  its  bulk 

and  density,  180. 
Vapors  differ  in  latent  heat,  130. 
Velocity  of  telegraphic  current,  401. 


Vibrations,  number  of,  required  for  differ- 
ent colors,  2uQ. 

Voltar  the  inven  or  of  the  voltaic  pile,  314. 
Volta's  theory.  313. 
Voltaic  pile,  314. 

"        "     theory  of,  315. 
Volta-electric  induction,  423. 

"      magueto-eleetric  induction,  442 
Voltameter,  362. 


W 


ATER,  decomposed  by  a  p 
ization  and  transfer,  851. 


rocess  of  polar- 


expansion of,  iu  cooling,  97. 
freezing  of,  in  red-hot  capsule,  164. 
frozen  by  its  own  evaporation  ,  183. 
specific  heat  of,  216. 
evolution  of  heat  of,  in  freezing,  117. 
maximum  density  of,  96. 
expansion  of,  in  freezing,  98. 
Weight  of  great  importance  in  chemistry, 
14.  (496. 

Wheatstone's     magneto-electric    machine, 
Wilde's  magneto-electric  machine,  489. 
Wollaston's  Cryophorus,  1*5. 
"          Hvpsometer,  133, 
"         Steam-bulb,  140. 


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Lands  from  River  Floods,  as  applied  to  the  Levees  of 
the  Mississippi.  By  William  Hewson,  Civil  Engineer. 
i  vol.  8vo,  cloth , , ,  2 .  oo 

TEE  IE  BOUIENGE  CHRORCGBAPH.  By  Bvt.  Capt 
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Illustrated,  4to,  cloth v. 3.00 

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HOLLEY  (A.  L.)  Railway  Practice.  American  and  Euro- 
pean Railway  Practice,  in  the  economical  Generation  of 
Steam,  including  the  Materials  and  Construction  of  Coal- 
burning  Boilers,  Combustion,  the  Variable  Blast,  Va- 
porization, Circulation,  Superheating,  Supplying  and 
Heating  Feed-water,  &c.,  and  the  Adaptation  of  Wood 
and  Coke-burning  Engines  to  Coal-burning ;  and  in 
Permanent  Way,  including  Road-bed,  Sleepers,  Rails, 
Joint-fastenings,  Street  Railways,  &c.,  &c.  By  Alex- 
ander L.  Holley,  B.  P.  With  77  lithographed  plates. 
i  vol.  folio,  cloth $12. oo 

•  *  •  "All  these  subjects  are  treated  by  the  author  in  both  an  intelligent  and  Intel 
ligible  manner.  The  facts  and  ideas  are  well  arranged,  and  presented  in  a  clear  and  sim- 
ple style,  accompanied  by  beautiful  engravings,  and  we  presume  the  work  will  be  re- 
garded as  indispensable  by  all  who  are  interested  in  a  knowledge  of  the  construction  o< 
railroads  and  rolling  stock,  or  the  working  of  locomotives."— Scientific  American. 

HUNT  (R.  M.)  Designs  for  the  Gateways  of  the  Southern 
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With  a  description  of  the  designs.  I  vol.  410,  illus- 
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KING  (W.  H.)  Lessons  and  Practical  Notes  on  Steam, 
the  Steam  Engine,  Propellers,  &c.,  &c.,  for  Young  Ma- 
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H.  King,  U.  S.  Navy.  Revised  by  Chief  Engineer  J. 
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8vo.     In  press , 

6 


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MIRIFIE  (Wm.)  Mechanical  Drawing.  A  Text-Book 
of  Geometrical  Drawing  for  the  use  of  Mechanics  and 
Schools,  in  which  the  Definitions  and  Rules  of  Geometry 
are  familiarly  explained ;  the  Practical  Problems  are  ar- 
ranged, from  the  most  simple  to  the  more  complex,  and 
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as  possible.  With  illustrations  for  Drawing  Plans,  Sec- 
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Introduction  to  Isometrical  Drawing,  and  an  Essay  on 
Linear  Perspective  and  Shadows.  Illustrated  with  over 
200  diagrams  engraved  on  steel.  By  Wm.  Minifie, 
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WILLIAMSON.  Practical  Tables  in  Meteorology  and 
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CULLEY.  A  Hand-Book  of  Practical  Telegraphy.  By 
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P3PE.     Modern  Practice  of  the  Electric  Telegraph.     For 
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POTTERY,  Materials  and  Manufacture  of  Terra  Cotta, 
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PIERCE  (Prof.  Bcnj.)  System  of  Analytical  Mechanics. 
Physical  and  Celestial  Mechanics,  by  Benjamin  Pierce, 
Perkins  Professor  of  Astronomy  and  Mathematics  in 
Harvard  University,  and  Consulting  Astronomer  of  the 
American  Ephcmeris  and  Nautical  Almanac.  Developed 
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which  I  may  hare  presumed  to  add  is  not  wholly  lustreless  in  the  co  lection,— I  snail  fe«l 
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PLYMPTON.  The  Blow-Pipe  ;  a  System  of  Instruction  in 
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Examination  of  Metallic  Combinations.  Second  edi- 
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POOK  (S.  M.)  Method  of  Comparing  the  Lanes  and 
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ROGERS  (H.  D.)  Geology  of  Pennsylvania.  A  complete 
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8 


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SUBMARINE  BLASTING  IN  BOSTON  HARBOR, 
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of  Engineers,  and  Brevet  Major-General,  United 
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SHAFFNER  (T.  P.)  Telegraph  Manual.  A  complete 
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with  625  illustrations.  By  Tal.  P.  Shaffher,  of  Ken- 
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SILVERSMITH  (Julius).  A  Practical  Hand-Book  for  Mi- 
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recent  improvements  in  the  disintegration,  amalgama 
tion,  smelting,  and  parting  of  the  Precious  Ores,  with  a 
Comprehensive  Digest  of  the  Mining  Laws.  Great!* 
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SIMM'S  LEVELLING.  A  Treatise  on  the  Principles  and 
Practice  of  Levelling,  showing  its  application  to  pur- 
poses of  Railway  Engineering  and  the  Construction 
of  Roads,  &c.  By  Frederick  W.  Simms,  C.  Ek 
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SUBMARINE  WARFARE,  Offensive  and  Defensive, 
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PLATTNER'S  BLOW-PIPE  ANALYSIS.  A  Complete 
Guide  to  Qualitative  and  Quantitative  Examinations 
with  the  Blow-Pipe.  Revised  and  enlarged  by  Prof. 
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DEIDRICH'S  Theory  of  Strains  for  the  Construction  of 
Bridges,  Roofs  and  Cranes.  Illustrated  with  plates 
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ST1LLMAN  (Paul).  Steam  Engine  Indicator,  and  the 
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New  edition,  i  vol.  1 2mo,  flexible  cloth i.oo 

RANMELSBERG'S  Guide  to  Quantitative  Chemical  An- 
alysis, especially  of  Minerals  and  Furnace  Products. 
Translated  by  Prof.  J.  Towler.  8vo,  cloth 2.25 

SWEET  (S.  H  )  Special  Report  on  Coal ;  showing  its 
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York,  and  the  principal  cities  on  the  Atlantic  Coast. 
By  S.  H.  Sweet.  With  maps,  i  vol.,  8vo,  cloth 3.00 

INTRODUCTION  TO  CHEMICAL  PHYSICS,  Designed 
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WALKER  (W.  H. )  Screw  Propulsion.  Notes  on  Screw 
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EXAMINATION  OF  THE  TELEGRAPHIC  APPARA- 
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P.  VAN  NOSTRAND  8  PUBLICATIONS. 

WEISBACH'S  MECHANICS.  New  and  revised  edition. 
A  Manual  of  the  Mechanics  of  Engineering,  and  of 
the  Construction  of  Machines.  By  Julius  Weisbarh, 
PH.  D.  Translated  from  the  fourth  augmented  and 
improved  German  edition,  by  Eckley  B.  Coxe,  A..  M., 
Mining  Engineer.  Vo).  I. — Theoretical  Mechanics. 
i  vol.  Svo,  1,100  pages,  and  902  wood-cut  illustra- 
tions, printed  from  electrotype  copies  of  those  of  the 

best  German  edition $10.00 

ABSTRACT  OF  CONTENTS. — Introduction  to  the  Cal- 
culus— The  General  Principles  of  Mechanics — Pho- 
ronomics,  or  the  Purely  Mathematical  Theory  of 
Motion — Statics  of  Rigid  Bodies — The  Application 
of  Statics  to  Elasticity  and  Strength — Dynamics  of 
Rigid  Bodies — Statics  of  Fluids — Dynamics  of  Fluids 
— The  Theory  of  Oscillation,  etc. 

"  The  present  edition  is  an  entirely  new  work,  greatly  extended  and  very  much  im- 
proved. It  forms  a  text-book  which  must  find  its  way  into  the  hands,  not  only  of  every 
student,  but  of  every  engineer  who  desires  to  refresh  his  memory  or  acquire  clear  ideal 
on  doubtful  points." — The  Technologist. 

WARD  (J.  H.)  Steam  for  the  Million.  A  popular  Trea- 
tise on  Steam  and  its  Application  to  the  useful  Arts, 
especially  to  Navigation.  By  J.  H.  Ward,  Com- 
mander U.  S.  Navy.  New  and  revised  edition,  i 
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WHILDEN  (J.  K.)  On  the  Strength  of  Materials  used 
in  Engineering  Construction.  By  J.  K.  Whilden. 
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WILLIAMSON  (R.  S.)  On  the  use  of  the  Barometer  on 
Surveys  and  Reconnaissances.  Part  I.  Meteorology 
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rometric Hypsometry.  By  R.  S.  Williamson,  Bvt. 
Lieut. -Col.  U.  S.  A.,  Major  Corps  of  Engineers. 
With  Illustrative  Tables  and  Engravings.  Paper 
No.  15,  Professional  Papers,  Corps  of  Engineers. 

i  vol.  4to,  cloth , 15.00 

11 


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EOEBLING  (J.  A.)  Long  and  Short  Span  Railway 
Bridges.  By  John  A.  Roebling,  C.  E,  Illustrated 
with  large  copperplate  engravings  of  plans  and  views. 
Imperial  folio,  cloth $2  5 .  co 

CLARKE  (T.  C.)  Description  of  the  Iron  Railway 
Bridge  over  the  Mississippi  River,  at  Quincy,  Illi- 
nois. By  Thomas  Curtis  Clarke,  Chief  Engineer. 
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cloth 7 . 50 

TUNNER  (P.)  A  Treatise  on  Roll-Turning  for  the 
manufacture  of  Iron.  By  Peter  Tunner.  Trans- 
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sylvania Steel  Works,  with  numerous  engravings 
and  wood-cuts,  i  vol.  8vo,  text,  and  fol.  vol.  Plates, 
cloth 10.  oo 

ISHERWOOD  (B.  F.)  Engineering  Precedents  for  Steam 
Machinery.  Arranged  in  the  most  practical  and 
useful  manner  for  Engineers.  By  B.  F.  Isher- 
wood,  Civil  Engineer,  U.  S.  Navy.  With  illustra- 
tions. Two  volumes  in  one.  8vo,  cloth 2 . 50 

3AUERMAN.  Treatise  on  the  Metallurgy  of  Iron,  con- 
taining outlines  of  the  History  of  Iron  Manufacture, 
methods  of  Assay,  and  analysis  of  Iron  Ores,  pro- 
cesses of  manufacture  of  Iron  and  Steel,  etc.,  etc. 
By  H.  Bauerman.  First  American  edition.  Re- 
vised and  enlarged,  with  an  appendix  on  the  Martin 
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the  subject,  as  well  as  in  all  technical  and  scientific  libraries"— Scientific  American. 

ELIOT  &  STORER'S  Manual  of  Qualitative  Chemical 
Analysis.  New  edition,  revised.  By  Prof.  W.  R. 

Nichols.     1 2mo,  illustrated 1.50 

12 


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NUGENT.  Treatise  on  Optics  :  or,  Light  and  Sight,  the- 
oretically and  practically  treated  ;  with  the  applica- 
tion to  Fine  Art  and  Industrial  Pursuits.  By  E. 
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"  This  book  is  of  a  practical  rather  than  a  theoretical  kind,  and  is  designed  to  afford 
accurate  and  complete  information  to  all  interested  in  applications  of  the  science.  —  Round 
JtibU. 

SABINE.  HISTORY  AND  PROGRESS  OF  THE  ELEC- 
TRIC TELEGRAPH.  By  Robert  Sabine,  C.E.  2d 
edition,  with  additions.  Fully  illustrated.  i2mo,  clo.  1.25 

GLYNN  (J.)  Treatise  on  the  Power  of  Water,  as  applied 
to  drive  Flour  Mills,  and  to  give  motion  to  Tur- 
bines and  other  Hydrostatic  Engines.  By  Joseph 
Glynn.  Third  edition,  revised  and  enlarged,  with 
numerous  illustrations.  1  2  mo,  cloth  ............  1.25 

PRIME.  TREATISE  ON  ORE  DEPOSITS.  By  Bern- 
hard  Von  Cotta.  Translated  from  the  Second  Ger- 
man edition  by  Frederick  Prime,  Jr.  ,  Mining  Engi- 
neer, and  revised  by  the  Author.  With  numerous 
illustrations.  8vo,  cloth  .......................  4  .  oo 


A  Handy  Book  for  the  Calculation  of  Strains 
in  Girders  and  similar  Structures,  and  their  Strength, 
consisting  of  Formulae  and  corresponding  Diagrams, 
with  numerous  details  for  practical  application.  By 
William  Humber.  i2mo,  fully  illustrated,  cloth.  .  .  2.50 

6ILLMORE.  Engineer  and  Artillery  Operations  against 
Charleston,  1863.  By  Major-General  Q.  A.  Gill- 
more.  With  76  lithographic  plates.  Svo,  cloth  ...  10.00 

•  -  Supplementary  Report  to  the  above,  with  7  litho- 

graphed maps  and  views.     Svo,  cloth  ...........     5.00 

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AUCHINCLOSS.  Link  and  Valve  Motions  Simplified. 
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useful  Tables.  By  W.  S.  Auchincloss.  8vo.,  cloth,  $3  oc 

JOYNSON.    METALS   USED  IN   CONSTRUCTION- 

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THE  ART  OF  GRAINING.  How  Acquired  and  How 
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VAN  BUREN.  Investigations  of  Formulas,  for  the  strength 
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JOYNSON.      Designing  and  Construction  of  Machine 

Gearing.    Illustrated,  8vo.,  cloth, a  oo 

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COIGNET-BETON,  and  other  Artificial  Stone.     By  Q.  A. 

Gillmore.    Illustrated  with  9  Plates.     8vo,  cloth 2.50* 

FREE  HAND  DRAWING,  a  Guide  to  Ornamental,  Fig- 
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THE  EARTH'S  CRUST.     A  handy  Outline  of  Geology. 

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DICTIONARY  of  Manufactures,  Mining,  Machinery,  and 
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cloth, 2  oo 

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BURT,  Key  to  the  Solar  Compass,  and  Surveyor's  Com- 
panion. By  W.  A.  Burt  Second  edition.  Pocket- 
book  form,  tuck $2.  <jo 

A  TREATISE  ON  THE  RICHARDS  STEAM-ENGINE 
INDICATOR,  with  Directions  for  its  Use.  By  Chas. 
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as  developed  by  American  Practice,  with  an  Appendix 
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ON  THE  FILTRATION  OF  RIVER  WATERS,  for  the 

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Louis.  By  J.  P.  Kirkwood,  Civil  Engineer.  Illus- 
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THE  PLANE-TABLE  AND  ITS  USE  IN  TOPOGRAPH- 
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REPORT  on  Machinery  and  Processes  of  the  Industrial 
Arts  and  Apparatus  of  the  Exact  Sciences.  By  F.  A. 
P.  Barnard,  LL.  D.  Paris  Universal  Exposition, 
1867.  i  vol.  8vo,  cloth 5.00 

IRON  TRUSS  BRIDGES  FOR  RAILROADS.      The 

Method  of  Calculating  Strains  in  Trusses,  with  a 
JCareful  Comparison  of  the  most  Prominent  Trusses  in 
Reference  to  Economy  in  Combination,  etc.  By 
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USEFUL    INFORMATION    FOR    RAILWAY    MEN. 

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pocket J.O? 

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Vol.  i.     January  to  December,  1869.     Cloth $5.00 


2.  '  June,  1870. 

3.  July  to  December,  1870. 

4.  January  to  June,  1871. 

5.  July  to  December,  1871. 


300 
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6.     January  to  June,          1872. 

VAN  NOSTRAND'S  MAGAZINE  consists  of  Articles  St- 
lected  and  Matter  Condensed  from  all  the  Engineering  Serial 
Publications  of  Europe  and  America,  together  with  Original 
Articles. 

Few  active  engineers  01  artisans  can  take  all  or  most  of  the 
professional  newspapers  ;  none  can  afford  the  time  to  wade 
through  the  columns  of  the  whole  scientific  press  to  get  at  the 
really  important  news,  information,  and  opinions. 

The  object  of  this  Magazine  is  to  present  within  limits  of  space 
and  cost  that  all  can  afford,  the  cream  of  not  less  than  fifty  engi 
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The  French  and  German  Magazines  will  be  largely  translated. 
Papers  and  discussions  before  Societies  will  be  condensed. 
Professional  news  from  all  sources  will  be  compiled  at  length. 

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g]D I 

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University  of  California 

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